Participants were to receive TAS3351 700 mg, tablets, orally, QD, on Days 1-21 of each 21-day cycle.

Participants were to be enrolled in Part A2 (backfill) when a dose level in Part A1 was determined to be safe and preliminary antitumor activity was observed.

.NSCLC participants with C797S EGFR mutations were planned for enrollment in Part B (dose expansion) and were to receive the recommended Phase 2 dose established in Part A.

NSCLC participants with C797S EGFR mutations were planned for enrollment in Part C (Phase 2) and were to receive the recommended Phase 2 dose established in Part A

ORR was the proportion of participants experiencing a PR or CR according to RECIST v1.1 criteria. Evaluation of target lesions defined a CR as the disappearance of all target lesions and non-target lesions (if applicable), and normalization of tumor marker level; PR was defined as at least a 30% decrease in the sum of diameters of the target lesions, taking as a reference the baseline sum of diameters for all target lesion assessments. Evaluation of non-target lesions was defined as the persistence of one or more non-target lesion(s) and/or maintenance of tumor marker level above the normal limits. For both target and non-target evaluations, any pathological lymph node must have had a reduction in short axis to <10mm.

DOR was calculated for all responders from the date of first documentation of response (CR or PR) to the first documentation of objective tumor progression or death due to any cause, whichever occurred first. Evaluation of target lesions defined a CR as the disappearance of all target lesions and non-target lesions (if applicable), and normalization of tumor marker level; PR was defined as at least a 30% decrease in the sum of diameters of the target lesions, taking as a reference the baseline sum of diameters for all target lesion assessments. Evaluation of non-target lesions was defined as the persistence of one or more non-target lesion(s) and/or maintenance of tumor marker level above the normal limits. For both target and non-target evaluations, any pathological lymph node must have had a reduction in short axis to <10 mm.

DCR was the proportion of participants who achieved a CR, PR, or stable disease (SD). Evaluation of target lesions defined a CR as the disappearance of all target lesions and non-target lesions (if applicable), and normalization of tumor marker level; PR was defined as at least a 30% decrease in the sum of diameters of the target lesions, taking as a reference the baseline sum of diameters for all target lesion assessments. Evaluation of non-target lesions was defined as the persistence of one or more non-target lesion(s) and/or maintenance of tumor marker level above the normal limits. For both target and non-target evaluations, any pathological lymph node must have had a reduction in short axis <10 mm. SD was defined as neither sufficient shrinkage to qualify for PR nor sufficient increase to qualify for progressive disease (PD), referencing the smallest sum diameters while on study.

PFS was defined as the time from date of first dose to the date of documentation of disease progression, or date of death, whichever occurred first.

OS was measured from the date of first dose until the date of death due to any cause.

Cmax is the maximum observed plasma concentration within the dosing interval. Blood samples for pharmacokinetic (PK) analysis were collected at specified timepoints. A PK lead-in with a single TAS3351 dose on Cycle 1 Day -3, followed by PK sampling three days before the start of continuous daily dosing, was included to characterize the PK profile.

AUC24 is the area under the curve from the time of dosing up to time 24hours. Blood samples for PK analysis were collected at specified timepoints. A PK lead-in with a single TAS3351 dose on Cycle 1 Day -3, followed by PK sampling three days before the start of continuous daily dosing, was included to characterize the PK profile.

AUCinf is the area under the plasma concentration-time curve from time of dosing extrapolated to infinity. Blood samples for PK analysis were collected at specified timepoints. A PK lead-in with a single TAS3351 dose on Cycle 1 Day -3, followed by PK sampling three days before the start of continuous daily dosing, was included to characterize the PK profile.

Tmax is the time to maximum plasma concentration within the dosing interval. Blood samples for PK analysis were collected at specified timepoints. A PK lead-in with a single TAS3351 dose on Cycle 1 Day -3, followed by PK sampling three days before the start of continuous daily dosing, was included to characterize the PK profile.

T1/2 is the terminal elimination half-life. Blood samples for PK analysis were collected at specified timepoints. A PK lead-in with a single TAS3351 dose on Cycle 1 Day -3, followed by PK sampling three days before the start of continuous daily dosing, was included to characterize the PK profile.

Cmax is the maximum observed plasma concentration within the dosing interval. Blood samples for PK analysis were collected at specified timepoints. A PK lead-in with a single TAS3351 dose on Cycle 1 Day -3, followed by PK sampling three days before the start of continuous daily dosing, was included to characterize the PK profile.

AUC24 is the area under the curve from the time of dosing up to time 24hours. Blood samples for PK analysis were collected at specified timepoints. A PK lead-in with a single TAS3351 dose on Cycle 1 Day -3, followed by PK sampling three days before the start of continuous daily dosing, was included to characterize the PK profile.

AUCinf is the area under the plasma concentration-time curve from time of dosing extrapolated to infinity. Blood samples for PK analysis were collected at specified timepoints. A PK lead-in with a single TAS3351 dose on Cycle 1 Day -3, followed by PK sampling three days before the start of continuous daily dosing, was included to characterize the PK profile.

Tmax is the time to maximum plasma concentration within the dosing interval. Blood samples for PK analysis were collected at specified timepoints. A PK lead-in with a single TAS3351 dose on Cycle 1 Day -3, followed by PK sampling three days before the start of continuous daily dosing, was included to characterize the PK profile.

T1/2 is the terminal elimination half-life. Blood samples for PK analysis were collected at specified timepoints. A PK lead-in with a single TAS3351 dose on Cycle 1 Day -3, followed by PK sampling three days before the start of continuous daily dosing, was included to characterize the PK profile.

An AE was defined as any untoward medical occurrence in a participant administered a pharmaceutical product; it did not necessarily have to have a causal relationship with this treatment. A TEAE was defined as an AE that is starting or worsening at the time of or after the first dose of study drug administration and within 30 days after the last dose of study drug and did not necessarily have a causal relationship to the use of the study drug.

DOR was calculated for all responders from the date of first documentation of response (CR or PR) to the first documentation of objective tumor progression or death due to any cause, whichever occurred first. Evaluation of target lesions defined a CR as the disappearance of all target lesions and non-target lesions (if applicable), and normalization of tumor marker level; PR was defined as at least a 30% decrease in the sum of diameters of the target lesions, taking as a reference the baseline sum of diameters for all target lesion assessments. Evaluation of non-target lesions was defined as the persistence of one or more non-target lesion(s) and/or maintenance of tumor marker level above the normal limits. For both target and non-target evaluations, any pathological lymph node must have had a reduction in short axis to <10 mm.

PFS is the time from date of first dose to the date of documentation of disease progression, or date of death, whichever occurs first.

DCR was the proportion of participants who achieved a CR, PR, or SD. Evaluation of target lesions defined a CR as the disappearance of all target lesions and non-target lesions (if applicable), and normalization of tumor marker level; PR was defined as at least a 30% decrease in the sum of diameters of the target lesions, taking as a reference the baseline sum of diameters for all target lesion assessments. Evaluation of non-target lesions was defined as the persistence of one or more non-target lesion(s) and/or maintenance of tumor marker level above the normal limits. For both target and non-target evaluations, any pathological lymph node must have had a reduction in short axis <10 mm. SD was defined as neither sufficient shrinkage to qualify for PR nor sufficient increase to qualify for PD, referencing the smallest sum diameters while on study.

ORR was the proportion of participants experiencing a PR or CR according to RECIST v1.1 criteria. Evaluation of target lesions defined a CR as the disappearance of all target lesions and non-target lesions (if applicable), and normalization of tumor marker level; PR was defined as at least a 30% decrease in the sum of diameters of the target lesions, taking as a reference the baseline sum of diameters for all target lesion assessments. Evaluation of non-target lesions was defined as the persistence of one or more non-target lesion(s) and/or maintenance of tumor marker level above the normal limits. For both target and non-target evaluations, any pathological lymph node must have had a reduction in short axis to <10mm.

DOR was calculated for all responders from the date of first documentation of response (CR or PR) to the first documentation of objective tumor progression or death due to any cause, whichever occurred first. Evaluation of target lesions defined a CR as the disappearance of all target lesions and non-target lesions (if applicable), and normalization of tumor marker level; PR was defined as at least a 30% decrease in the sum of diameters of the target lesions, taking as a reference the baseline sum of diameters for all target lesion assessments. Evaluation of non-target lesions was defined as the persistence of one or more non-target lesion(s) and/or maintenance of tumor marker level above the normal limits. For both target and non-target evaluations, any pathological lymph node must have had a reduction in short axis to <10 mm.

PFS was defined as the time from date of first dose to the date of documentation of disease progression, or date of death, whichever occurred first.

DCR was the proportion of participants who achieved a CR, PR, or SD. Evaluation of target lesions defined a CR as the disappearance of all target lesions and non-target lesions (if applicable), and normalization of tumor marker level; PR was defined as at least a 30% decrease in the sum of diameters of the target lesions, taking as a reference the baseline sum of diameters for all target lesion assessments. Evaluation of non-target lesions was defined as the persistence of one or more non-target lesion(s) and/or maintenance of tumor marker level above the normal limits. For both target and non-target evaluations, any pathological lymph node must have had a reduction in short axis <10 mm. SD was defined as neither sufficient shrinkage to qualify for PR nor sufficient increase to qualify for PD, referencing the smallest sum diameters while on study.

The icORR was defined as percentage of participants experiencing a PR or CR. Evaluation of target lesions defined a CR as the disappearance of all target lesions and non-target lesions (if applicable), and normalization of tumor marker level; PR was defined as at least a 30% decrease in the sum of diameters of the target lesions, taking as a reference the baseline sum of diameters for all target lesion assessments. Evaluation of non-target lesions was defined as the persistence of one or more non-target lesion(s) and/or maintenance of tumor marker level above the normal limits. For both target and non-target evaluations, any pathological lymph node must have had a reduction in short axis to <10mm. The icORR was planned to be assessed based on ORR of central nerve system (CNS) lesions only.

The icDoR was planned to be calculated for all responders from the date of first documentation of response (CR or PR) to the first documentation of objective tumor progression or death due to any cause, whichever occurred first. Evaluation of target lesions defined a CR as the disappearance of all target lesions and non-target lesions (if applicable), and normalization of tumor marker level; PR was defined as at least a 30% decrease in the sum of diameters of the target lesions, taking as a reference the baseline sum of diameters for all target lesion assessments. Evaluation of non-target lesions was defined as the persistence of one or more non-target lesion(s) and/or maintenance of tumor marker level above the normal limits. For both target and non-target evaluations, any pathological lymph node must have had a reduction in short axis to <10 mm. The icDoR was planned to be assessed based on DoR of CNS lesions only.

OS was measured from the date of first dose until the date of death due to any cause.

The EORTC QLQ-C30 is a 30-item questionnaire meant to assess different aspects that define the quality of life of cancer participants and survivors. It facilitates insights into participants' physical, emotional, and social wellbeing, ultimately supporting more informed treatment decisions and care strategies. The questionnaire is divided into 4 parts, namely global health status/ quality of life, functional scales, symptom scales and single-item symptoms. Each item was meant to be scored on a scale of 1 (Not at all) to 4 (Very much). Scores obtained from each section are transformed to a 0-100 score. For the functional and global health status scales, higher scores indicate better functioning or quality of life. For symptom scales and single-item measures, higher scores indicate greater symptom severity.

The EQ-5D-5L is a standardized, generic, participant-reported instrument developed by the EuroQol Group to assess health-related quality of life across five dimensions: mobility, self-care, usual activities, pain/discomfort, and anxiety/depression. Participants were to rate five dimensions namely, mobility, self-care, usual activities, pain/discomfort and anxiety/depression. Each item is scores on a score of 1 (no problems) to 5 (extreme problems). The combination of responses forms a 5-digit health state which is converted into a single utility index score using a country-specific value set. Higher utility scores indicate better health-related quality of life.

Participants received TAS3351 200 mg, tablets, orally, QD, on Days 1 -21 of each 21-day cycle, for maximum duration of 94 days.

Participants received TAS3351 350 mg, tablets, orally, QD, on Days 1-21 of each 21-day cycle, for maximum duration of 46 days.

Participants received TAS3351 500 mg, tablets, orally, QD, on Days 1-21 of each 21-day cycle, for maximum duration of 87 days.

Total of all reporting groups

Participants received TAS3351 100 mg, tablets, orally, QD, on Days 1 -21 of each 21-day cycle, for maximum duration of 126 days.

Participants received TAS3351 200 mg, tablets, orally, QD, on Days 1 -21 of each 21-day cycle, for maximum duration of 94 days.

Participants received TAS3351 350 mg, tablets, orally, QD, on Days 1-21 of each 21-day cycle, for maximum duration of 46 days.

Participants received TAS3351 500 mg, tablets, orally, QD, on Days 1-21 of each 21-day cycle, for maximum duration of 87 days.

DLTs were defined as adverse events (AEs) graded by Common Terminology Criteria for Adverse Events Version 5.0 (CTCAE v5.0) assessed by the Investigator to be related to study treatment administration during Cycle 1 & included:Hematologic Toxicity;grade 4 neutropenia greater than[>]7days; febrile neutropenia (absolute neutrophil count [ANC] less than(<)1000 per cubic millimeter (1000/mm3) with fever greater than or equal to(≥)38.3 degree celsius (°C) or fever ≥38.0°C for > 1hour); grade 4 thrombocytopenia, Hepatic Toxicity: grade ≥3 total bilirubin >7days; grade 4 total bilirubin; Renal Toxicity:creatinine clearance(CrCl)<30 milliliters per minute (mL/min) for > 3days despite supportive care;Other Nonhematologic Toxicity:grade ≥3 nonhematologic toxicity with: grade 3 nausea, vomiting, diarrhea, or hyperglycemia, prolonged delay (>2 weeks) in initiating Cycle 2 due to treatment-related toxicity; Any death not clearly attributed to the underlying disease or extraneous causes.

The DLT Evaluable Population included all participants in the Dose Escalation, except backfill participants, who either experienced a DLT during the 1st cycle of treatment including Pharmacokinetic (PK) lead-in period, or who completed the 1st cycle without experiencing a DLT and with at least 80% of planned study treatments administered.

ORR was the proportion of participants experiencing a best overall response of partial response (PR) or complete response (CR) according to response evaluation criteria in solid tumors, version 1.1 (RECIST v1.1) criteria. Evaluation of target lesions defined a CR as the disappearance of all target lesions and non-target lesions (if applicable), and normalization of tumor marker level; PR was defined as at least a 30 percent (%) decrease in the sum of diameters of the target lesions, taking as a reference the baseline sum of diameters for all target lesion assessments. Evaluation of non-target lesions was defined as the persistence of one or more non-target lesion(s) and/or maintenance of tumor marker level above the normal limits. For both target and non-target evaluations, any pathological lymph node must have had a reduction in short axis to less than (<)10 millimeters (mm).

Due to Sponsor's decision to terminate the study early, Part B of the study was not conducted, and no participants were enrolled in Part B. Therefore, no data were collected for this outcome measure.

ORR was the proportion of participants experiencing a PR or CR according to RECIST v1.1 criteria. Evaluation of target lesions defined a CR as the disappearance of all target lesions and non-target lesions (if applicable), and normalization of tumor marker level; PR was defined as at least a 30% decrease in the sum of diameters of the target lesions, taking as a reference the baseline sum of diameters for all target lesion assessments. Evaluation of non-target lesions was defined as the persistence of one or more non-target lesion(s) and/or maintenance of tumor marker level above the normal limits. For both target and non-target evaluations, any pathological lymph node must have had a reduction in short axis to <10mm.

Due to Sponsor's decision to terminate the study early, Part C of the study was not conducted, and no participants were enrolled in Part C. Therefore, no data were collected for this outcome measure.

ORR was the proportion of participants experiencing a best overall response of PR or CR according to RECIST v1.1 criteria. Evaluation of target lesions defined a CR as the disappearance of all target lesions and non-target lesions (if applicable), and normalization of tumor marker level; PR was defined as at least a 30% decrease in the sum of diameters of the target lesions, taking as a reference the baseline sum of diameters for all target lesion assessments. Evaluation of non-target lesions was defined as the persistence of one or more non-target lesion(s) and/or maintenance of tumor marker level above the normal limits. For both target and non-target evaluations, any pathological lymph node must have had a reduction in short axis to <10mm.

The all treated population included all participants who received at least one dose of the study drug.

DOR was calculated for all responders from the date of first documentation of response (CR or PR) to the first documentation of objective tumor progression or death due to any cause, whichever occurred first. Evaluation of target lesions defined a CR as the disappearance of all target lesions and non-target lesions (if applicable), and normalization of tumor marker level; PR was defined as at least a 30% decrease in the sum of diameters of the target lesions, taking as a reference the baseline sum of diameters for all target lesion assessments. Evaluation of non-target lesions was defined as the persistence of one or more non-target lesion(s) and/or maintenance of tumor marker level above the normal limits. For both target and non-target evaluations, any pathological lymph node must have had a reduction in short axis to <10 mm.

The all treated population included all participants who received at least one dose of study drug.

DCR was the proportion of participants who achieved a CR, PR, or stable disease (SD). Evaluation of target lesions defined a CR as the disappearance of all target lesions and non-target lesions (if applicable), and normalization of tumor marker level; PR was defined as at least a 30% decrease in the sum of diameters of the target lesions, taking as a reference the baseline sum of diameters for all target lesion assessments. Evaluation of non-target lesions was defined as the persistence of one or more non-target lesion(s) and/or maintenance of tumor marker level above the normal limits. For both target and non-target evaluations, any pathological lymph node must have had a reduction in short axis <10 mm. SD was defined as neither sufficient shrinkage to qualify for PR nor sufficient increase to qualify for progressive disease (PD), referencing the smallest sum diameters while on study.

The all treated population included all participants who received at least one dose of study drug.

PFS was defined as the time from date of first dose to the date of documentation of disease progression, or date of death, whichever occurred first.

Due to Sponsor's decision to terminate the study early, Part A2 of the study was not conducted and no participants were enrolled in Part A2. Therefore, no data were collected for this outcome measure.

OS was measured from the date of first dose until the date of death due to any cause.

Due to Sponsor's decision to terminate the study early, Part A2 of the study was not conducted and no participants were enrolled in Part A2. Therefore, no data were collected for this outcome measure.

Cmax is the maximum observed plasma concentration within the dosing interval. Blood samples for pharmacokinetic (PK) analysis were collected at specified timepoints. A PK lead-in with a single TAS3351 dose on Cycle 1 Day -3, followed by PK sampling three days before the start of continuous daily dosing, was included to characterize the PK profile.

The PK population included all participants who received at least one dose of study drug and had at least one post-dose TAS3351 and/or TAS-05-14317 plasma concentration measurement. Overall number of participants analyzed is the number of participants with data available for analysis. Number analyzed are the number of participants with data available for analysis at specified time-point.

AUC24 is the area under the curve from the time of dosing up to time 24hours. Blood samples for PK analysis were collected at specified timepoints. A PK lead-in with a single TAS3351 dose on Cycle 1 Day -3, followed by PK sampling three days before the start of continuous daily dosing, was included to characterize the PK profile.

The PK population included all participants who received at least one dose of study drug and had at least one post-dose TAS3351 and/or TAS-05-14317 plasma concentration measurement. Overall number of participants analyzed is the number of participants with data available for analysis. Number analyzed are the number of participants with data available for analysis at specified time-point.

AUCinf is the area under the plasma concentration-time curve from time of dosing extrapolated to infinity. Blood samples for PK analysis were collected at specified timepoints. A PK lead-in with a single TAS3351 dose on Cycle 1 Day -3, followed by PK sampling three days before the start of continuous daily dosing, was included to characterize the PK profile.

The PK population included all participants who received at least one dose of study drug and had at least one post-dose TAS3351 and/or TAS-05-14317 plasma concentration measurement. Overall number of participants analyzed is the number of participants with data available for analysis.

Tmax is the time to maximum plasma concentration within the dosing interval. Blood samples for PK analysis were collected at specified timepoints. A PK lead-in with a single TAS3351 dose on Cycle 1 Day -3, followed by PK sampling three days before the start of continuous daily dosing, was included to characterize the PK profile.

The PK population included all participants who received at least one dose of study drug and had at least one post-dose TAS3351 and/or TAS-05-14317 plasma concentration measurement. Overall number of participants analyzed is the number of participants with data available for analysis. Number analyzed are the number of participants with data available for analysis at specified time-point.

T1/2 is the terminal elimination half-life. Blood samples for PK analysis were collected at specified timepoints. A PK lead-in with a single TAS3351 dose on Cycle 1 Day -3, followed by PK sampling three days before the start of continuous daily dosing, was included to characterize the PK profile.

The PK population included all participants who received at least one dose of study drug and had at least one post-dose TAS3351 and/or TAS-05-14317 plasma concentration measurement. Overall number of participants analyzed is the number of participants with data available for analysis.

Cmax is the maximum observed plasma concentration within the dosing interval. Blood samples for PK analysis were collected at specified timepoints. A PK lead-in with a single TAS3351 dose on Cycle 1 Day -3, followed by PK sampling three days before the start of continuous daily dosing, was included to characterize the PK profile.

The PK population included all participants who received at least one dose of study drug and had at least one post-dose TAS3351 and/or TAS-05-14317 plasma concentration measurement. Overall number of participants analyzed is the number of participants with data available for analysis. Number analyzed are the number of participants with data available for analysis at specified time-point.

AUC24 is the area under the curve from the time of dosing up to time 24hours. Blood samples for PK analysis were collected at specified timepoints. A PK lead-in with a single TAS3351 dose on Cycle 1 Day -3, followed by PK sampling three days before the start of continuous daily dosing, was included to characterize the PK profile.

The PK population included all participants who received at least one dose of study drug and had at least one post-dose TAS3351 and/or TAS-05-14317 plasma concentration measurement. Overall number of participants analyzed is the number of participants with data available for analysis. Number analyzed are the number of participants with data available for analysis at specified time-point.

AUCinf is the area under the plasma concentration-time curve from time of dosing extrapolated to infinity. Blood samples for PK analysis were collected at specified timepoints. A PK lead-in with a single TAS3351 dose on Cycle 1 Day -3, followed by PK sampling three days before the start of continuous daily dosing, was included to characterize the PK profile.

The PK population included all participants who received at least one dose of study drug and had at least one post-dose TAS3351 and/or TAS-05-14317 plasma concentration measurement. Overall number of participants analyzed is the number of participants with data available for analysis.

Tmax is the time to maximum plasma concentration within the dosing interval. Blood samples for PK analysis were collected at specified timepoints. A PK lead-in with a single TAS3351 dose on Cycle 1 Day -3, followed by PK sampling three days before the start of continuous daily dosing, was included to characterize the PK profile.

The PK population included all participants who received at least one dose of study drug and had at least one post-dose TAS3351 and/or TAS-05-14317 plasma concentration measurement. Overall number of participants analyzed is the number of participants with data available for analysis. Number analyzed are the number of participants with data available for analysis at specified time-point.

T1/2 is the terminal elimination half-life. Blood samples for PK analysis were collected at specified timepoints. A PK lead-in with a single TAS3351 dose on Cycle 1 Day -3, followed by PK sampling three days before the start of continuous daily dosing, was included to characterize the PK profile.

The PK population included all participants who received at least one dose of study drug and had at least one post-dose TAS3351 and/or TAS-05-14317 plasma concentration measurement. Overall number of participants analyzed is the number of participants with data available for analysis.

An AE was defined as any untoward medical occurrence in a participant administered a pharmaceutical product; it did not necessarily have to have a causal relationship with this treatment. A TEAE was defined as an AE that is starting or worsening at the time of or after the first dose of study drug administration and within 30 days after the last dose of study drug and did not necessarily have a causal relationship to the use of the study drug.

Due to Sponsor's decision to terminate the study early, Parts B and C of the study were not conducted, and no participants were enrolled in Parts B and C. Therefore, no data were collected for this outcome measure.

DOR was calculated for all responders from the date of first documentation of response (CR or PR) to the first documentation of objective tumor progression or death due to any cause, whichever occurred first. Evaluation of target lesions defined a CR as the disappearance of all target lesions and non-target lesions (if applicable), and normalization of tumor marker level; PR was defined as at least a 30% decrease in the sum of diameters of the target lesions, taking as a reference the baseline sum of diameters for all target lesion assessments. Evaluation of non-target lesions was defined as the persistence of one or more non-target lesion(s) and/or maintenance of tumor marker level above the normal limits. For both target and non-target evaluations, any pathological lymph node must have had a reduction in short axis to <10 mm.

Due to Sponsor's decision to terminate the study early, Parts B and C of the study were not conducted, and no participants were enrolled in Parts B and C. Therefore, no data were collected for this outcome measure.

PFS is the time from date of first dose to the date of documentation of disease progression, or date of death, whichever occurs first.

Due to Sponsor's decision to terminate the study early, Parts B and C of the study were not conducted, and no participants were enrolled in Parts B and C. Therefore, no data were collected for this outcome measure.

DCR was the proportion of participants who achieved a CR, PR, or SD. Evaluation of target lesions defined a CR as the disappearance of all target lesions and non-target lesions (if applicable), and normalization of tumor marker level; PR was defined as at least a 30% decrease in the sum of diameters of the target lesions, taking as a reference the baseline sum of diameters for all target lesion assessments. Evaluation of non-target lesions was defined as the persistence of one or more non-target lesion(s) and/or maintenance of tumor marker level above the normal limits. For both target and non-target evaluations, any pathological lymph node must have had a reduction in short axis <10 mm. SD was defined as neither sufficient shrinkage to qualify for PR nor sufficient increase to qualify for PD, referencing the smallest sum diameters while on study.

Due to Sponsor's decision to terminate the study early, Parts B and C of the study were not conducted, and no participants were enrolled in Parts B and C. Therefore, no data were collected for this outcome measure.

ORR was the proportion of participants experiencing a PR or CR according to RECIST v1.1 criteria. Evaluation of target lesions defined a CR as the disappearance of all target lesions and non-target lesions (if applicable), and normalization of tumor marker level; PR was defined as at least a 30% decrease in the sum of diameters of the target lesions, taking as a reference the baseline sum of diameters for all target lesion assessments. Evaluation of non-target lesions was defined as the persistence of one or more non-target lesion(s) and/or maintenance of tumor marker level above the normal limits. For both target and non-target evaluations, any pathological lymph node must have had a reduction in short axis to <10mm.

Due to Sponsor's decision to terminate the study early, Parts B and C of the study were not conducted, and no participants were enrolled in Parts B and C. Therefore, no data were collected for this outcome measure.

DOR was calculated for all responders from the date of first documentation of response (CR or PR) to the first documentation of objective tumor progression or death due to any cause, whichever occurred first. Evaluation of target lesions defined a CR as the disappearance of all target lesions and non-target lesions (if applicable), and normalization of tumor marker level; PR was defined as at least a 30% decrease in the sum of diameters of the target lesions, taking as a reference the baseline sum of diameters for all target lesion assessments. Evaluation of non-target lesions was defined as the persistence of one or more non-target lesion(s) and/or maintenance of tumor marker level above the normal limits. For both target and non-target evaluations, any pathological lymph node must have had a reduction in short axis to <10 mm.

Due to Sponsor's decision to terminate the study early, Parts B and C of the study were not conducted, and no participants were enrolled in Parts B and C. Therefore, no data were collected for this outcome measure.

PFS was defined as the time from date of first dose to the date of documentation of disease progression, or date of death, whichever occurred first.

Due to Sponsor's decision to terminate the study early, Parts B and C of the study were not conducted, and no participants were enrolled in Parts B and C. Therefore, no data were collected for this outcome measure.

DCR was the proportion of participants who achieved a CR, PR, or SD. Evaluation of target lesions defined a CR as the disappearance of all target lesions and non-target lesions (if applicable), and normalization of tumor marker level; PR was defined as at least a 30% decrease in the sum of diameters of the target lesions, taking as a reference the baseline sum of diameters for all target lesion assessments. Evaluation of non-target lesions was defined as the persistence of one or more non-target lesion(s) and/or maintenance of tumor marker level above the normal limits. For both target and non-target evaluations, any pathological lymph node must have had a reduction in short axis <10 mm. SD was defined as neither sufficient shrinkage to qualify for PR nor sufficient increase to qualify for PD, referencing the smallest sum diameters while on study.

Due to Sponsor's decision to terminate the study early, Parts B and C of the study were not conducted, and no participants were enrolled in Parts B and C. Therefore, no data were collected for this outcome measure.

The icORR was defined as percentage of participants experiencing a PR or CR. Evaluation of target lesions defined a CR as the disappearance of all target lesions and non-target lesions (if applicable), and normalization of tumor marker level; PR was defined as at least a 30% decrease in the sum of diameters of the target lesions, taking as a reference the baseline sum of diameters for all target lesion assessments. Evaluation of non-target lesions was defined as the persistence of one or more non-target lesion(s) and/or maintenance of tumor marker level above the normal limits. For both target and non-target evaluations, any pathological lymph node must have had a reduction in short axis to <10mm. The icORR was planned to be assessed based on ORR of central nerve system (CNS) lesions only.

Due to Sponsor's decision to terminate the study early, Parts B and C of the study were not conducted, and no participants were enrolled in Parts B and C. Therefore, no data were collected for this outcome measure.

The icDoR was planned to be calculated for all responders from the date of first documentation of response (CR or PR) to the first documentation of objective tumor progression or death due to any cause, whichever occurred first. Evaluation of target lesions defined a CR as the disappearance of all target lesions and non-target lesions (if applicable), and normalization of tumor marker level; PR was defined as at least a 30% decrease in the sum of diameters of the target lesions, taking as a reference the baseline sum of diameters for all target lesion assessments. Evaluation of non-target lesions was defined as the persistence of one or more non-target lesion(s) and/or maintenance of tumor marker level above the normal limits. For both target and non-target evaluations, any pathological lymph node must have had a reduction in short axis to <10 mm. The icDoR was planned to be assessed based on DoR of CNS lesions only.

Due to Sponsor's decision to terminate the study early, Parts B and C of the study were not conducted, and no participants were enrolled in Parts B and C. Therefore, no data were collected for this outcome measure.

OS was measured from the date of first dose until the date of death due to any cause.

Due to Sponsor's decision to terminate the study early, Parts B and C of the study were not conducted, and no participants were enrolled in Parts B and C. Therefore, no data were collected for this outcome measure.

The EORTC QLQ-C30 is a 30-item questionnaire meant to assess different aspects that define the quality of life of cancer participants and survivors. It facilitates insights into participants' physical, emotional, and social wellbeing, ultimately supporting more informed treatment decisions and care strategies. The questionnaire is divided into 4 parts, namely global health status/ quality of life, functional scales, symptom scales and single-item symptoms. Each item was meant to be scored on a scale of 1 (Not at all) to 4 (Very much). Scores obtained from each section are transformed to a 0-100 score. For the functional and global health status scales, higher scores indicate better functioning or quality of life. For symptom scales and single-item measures, higher scores indicate greater symptom severity.

Due to Sponsor's decision to terminate the study early, Part C of the study was not conducted, and no participants were enrolled in Part C. Therefore, no data were collected for this outcome measure.

The EQ-5D-5L is a standardized, generic, participant-reported instrument developed by the EuroQol Group to assess health-related quality of life across five dimensions: mobility, self-care, usual activities, pain/discomfort, and anxiety/depression. Participants were to rate five dimensions namely, mobility, self-care, usual activities, pain/discomfort and anxiety/depression. Each item is scores on a score of 1 (no problems) to 5 (extreme problems). The combination of responses forms a 5-digit health state which is converted into a single utility index score using a country-specific value set. Higher utility scores indicate better health-related quality of life.

Due to Sponsor's decision to terminate the study early, Part C of the study was not conducted, and no participants were enrolled in Part C. Therefore, no data were collected for this outcome measure.

Participants received TAS3351 100 mg, tablets, orally, QD, on Days 1 -21 of each 21-day cycle, for a maximum duration of 126 days.

Participants received TAS3351 200 mg, tablets, orally, QD, on Days 1 -21 of each 21-day cycle, for a maximum duration of 94 days.

Participants received TAS3351 350 mg, tablets, orally, QD, on Days 1-21 of each 21-day cycle, for a maximum duration of 46 days.

Participants received TAS3351 500 mg, tablets, orally, QD, on Days 1-21 of each 21-day cycle, for a maximum duration of 87 days.