OS was defined as the time from the date of randomization to the date of death due to any cause. Kaplan-Meier estimate for the median OS is presented, along with associated 95% confidence interval, estimated using the Brookmeyer-Crowley method.

mITT population: All randomized participants whether or not randomized intervention was administered, excluding those who were first dosed or randomized after the date of DIL requesting immediate discontinuation of feladilimab /placebo. Participants were analyzed based on the study intervention to which the participant was randomized

OS was defined as the time from the date of randomization until the date of death due to any cause. CPS was defined as the ratio of the combined number of PD-L1 expressing tumor cells and immune cells (lymphocytes and macrophages) to the total number of viable tumor cells. Kaplan-Meier estimate for the median OS is presented, along with associated 95% confidence interval, estimated using the Brookmeyer-Crowley method.

Data for participants with PD-L1 CPS ≥1 in mITT population are presented.

PFS per Response Evaluation Criteria in Solid Tumors (RECIST) version (v)1.1 was defined as the time from the date of randomization to the date of first documented disease progression or death due to any cause, whichever occurs first. Kaplan-Meier estimate for the median PFS is presented, along with associated 95% confidence interval, estimated using the Brookmeyer-Crowley method.

All participants in the mITT population were analyzed

PFS per RECIST v1.1 was defined as the time from the date of randomization until the date of disease progression or death due to any cause, whichever occurs first. CPS was defined as the ratio of the combined number of PD-L1 expressing tumor cells and immune cells (lymphocytes and macrophages) to the total number of viable tumor cells. Kaplan-Meier estimate for the median PFS is presented, along with associated 95% confidence interval, estimated using the Brookmeyer-Crowley method.

Data for participants with PD-L1 CPS ≥1 in mITT population are presented.

Milestone OS rate at 12, 24, and 36 months was not evaluated.

mITT population. All participants were on study for <12 months. The maximum duration of follow-up was approximately 7 months.

Milestone OS rate at 12, 24, and 36 months was not evaluated. CPS was defined as the ratio of the combined number of PD-L1 expressing tumor cells and immune cells (lymphocytes and macrophages) to the total number of viable tumor cells.

Data for participants with PD-L1 CPS ≥1 in mITT population were to be presented. All participants were on study for <12 months. The maximum duration of follow-up was approximately 7 months.

ORR per RECIST v1.1 was defined as the proportion of the participants who have a complete response (CR) or partial response (PR) as the best overall response per RECIST v1.1 based upon investigator assessment. As a randomized double-blind study in which primary endpoints are OS and PFS, the confirmation of CR and PR was not required. Rate and associated 2-sided 95 percent Exact (Clopper-Pearson) Confidence Intervals are provided for each treatment arm which are unadjusted.

All participants in the mITT population were analyzed

ORR per RECIST v1.1 was defined as the proportion of the participants who have a complete response (CR) or partial response (PR) as the best overall response per RECIST v1.1 based upon investigator assessment. As a randomized double-blind study in which primary endpoints are OS and PFS, the confirmation of CR and PR was not required. Rate and associated 2-sided 95 percent Exact (Clopper-Pearson) Confidence Intervals are provided for each treatment arm which are unadjusted. CPS was defined as the ratio of the combined number of PD-L1 expressing tumor cells and immune cells (lymphocytes and macrophages) to the total number of viable tumor cells.

Data for participants with PD-L1 CPS ≥1 in mITT population are presented.

DCR per RECIST v1.1 based upon investigator assessment, was defined as the percentage of participants with a best overall response of CR or PR at any time plus stable disease (SD) meeting the minimum time of 15 weeks. A status of SD≥15 weeks will be assigned if the follow-up disease assessment has met the SD criteria at least once after the date of randomization at a minimum of 14 weeks (98 days) considering a one-week visit window. Rate and associated 2-sided 95 percent Exact (Clopper-Pearson) Confidence Intervals are provided for each treatment arm which are unadjusted.

All participants in the mITT population were analyzed

DCR per RECIST v1.1 based upon investigator assessment, was defined as the percentage of participants with a best overall response of CR or PR at any time plus stable disease (SD) meeting the minimum time of 15 weeks. A status of SD≥15 weeks will be assigned if the follow-up disease assessment has met the SD criteria at least once after the date of randomization at a minimum of 14 weeks (98 days) considering a one-week visit window. Rate and associated 2-sided 95 percent Exact (Clopper-Pearson) Confidence Intervals are provided for each treatment arm which are unadjusted. CPS was defined as the ratio of the combined number of PD-L1 expressing tumor cells and immune cells (lymphocytes and macrophages) to the total number of viable tumor cells.

Data for participants with PD-L1 CPS ≥1 in mITT population are presented.

DoR per RECIST v1.1 is defined as the time from first documented evidence of CR or PR until first documented disease progression per RECIST v1.1 based upon investigator assessment or death due to any cause, whichever occurs first, among participants who demonstrated CR or PR as the best overall response per RECIST v1.1. Kaplan-Meier estimate for the median DoR is presented, along with associated 95% confidence interval, estimated using the Brookmeyer-Crowley method.

Data for participants with a best overall response of CR or PR in mITT population are presented.

DoR per RECIST v1.1 is defined as the time from first documented evidence of CR or PR until first documented disease progression per RECIST v1.1 based upon investigator assessment or death due to any cause, whichever occurs first, among participants who demonstrated CR or PR as the best overall response per RECIST v1.1. Kaplan-Meier estimate for the median DoR is presented, along with associated 95% confidence interval, estimated using the Brookmeyer-Crowley method. CPS was defined as the ratio of the combined number of PD-L1 expressing tumor cells and immune cells (lymphocytes and macrophages) to the total number of viable tumor cells.

Data for participants with a best overall response of CR or PR in mITT population with PD-L1 CPS ≥1 are presented.

An AE is any untoward medical occurrence in a clinical study participant, temporally associated with the use of a study intervention, whether or not considered related to the study intervention

Safety Population: All randomized participants who took at least 1 dose of study intervention. Participants were analyzed according to the actual study intervention received. An additional participant was randomized after the data cut off and received pembrolizumab. Therefore, participant was included in safety analysis.

SAE was defined as any untoward medical occurrence that, at any dose, resulted in death, was life-threatening, required inpatient hospitalization or prolongation of existing hospitalization, resulted in persistent or significant disability/incapacity, was a congenital anomaly/birth defect and other situations according to medical or scientific judgement.

Safety Population. An additional participant was randomized after the data cut-off and received pembrolizumab. Therefore, this participant was included in safety analysis.

AESI were defined as events of potential immunologic etiology, including immune-related AEs (irAEs).

Safety Population. An additional participant was randomized after the data cut-off and received pembrolizumab. Therefore, this participant was included in safety analysis.

Any untoward or unfavorable medical occurrence in a participant, including any abnormal sign (for example, abnormal physical exam or laboratory finding), symptom, or disease, temporally associated with the participant's participation in the research, whether or not considered related to the participant's participation in the research. CPS was defined as the ratio of the combined number of PD-L1 expressing tumor cells and immune cells (lymphocytes and macrophages) to the total number of viable tumor cells.

Data for participants with PD-L1 CPS ≥1 in the safety population are presented. An additional participant was randomized after the data cut-off and received pembrolizumab. Therefore, this participant was included in safety analysis.

SAE was defined as any untoward medical occurrence that, at any dose, resulted in death, was life-threatening, required inpatient hospitalization or prolongation of existing hospitalization, resulted in persistent or significant disability/incapacity, was a congenital anomaly/birth defect and other situations according to medical or scientific judgement. CPS was defined as the ratio of the combined number of PD-L1 expressing tumor cells and immune cells (lymphocytes and macrophages) to the total number of viable tumor cells.

Data for participants with PD-L1 CPS ≥1 in the safety population are presented. An additional participant was randomized after the data cut-off and received pembrolizumab. Therefore, this participant was included in safety analysis.

AESI were defined as events of potential immunologic etiology, including immune-related AEs (irAEs). CPS was defined as the ratio of the combined number of PD-L1 expressing tumor cells and immune cells (lymphocytes and macrophages) to the total number of viable tumor cells.

Data for participants with PD-L1 CPS ≥1 in the safety population are presented. An additional participant was randomized after the data cut-off and received pembrolizumab. Therefore, this participant was included in safety analysis.

An AE was defined as any untoward medical occurrence in a clinical study participant, temporally associated with the use of a study intervention, whether or not considered related to the study intervention. Severity for each AE was reported during the study and assigned a grade according to the NCI-CTCAE v5.0. from Grade 1 through Grade 5. Grade 1= mild toxicity; Grade 2 = moderate toxicity; Grade 3 = severe toxicity; Grade 4 = life-threatening or disabling toxicity, Grade 5 = death related to toxicity.

Safety Population. An additional participant was randomized after the data cut-off and received pembrolizumab. Therefore, this participant was included in safety analysis.

A SAE was defined as any untoward medical occurrence that, at any dose resulted in death, was life-threatening, required inpatient hospitalization or prolongation of existing hospitalization, resulted in persistent disability/incapacity, is a congenital anomaly/birth defect, any other situation such as important medical events according to medical or scientific judgement. Severity for each SAE was reported during the study and assigned a grade according to the NCI-CTCAE v5.0. from Grade 1 through Grade 5. Grade 1= mild toxicity; Grade 2 = moderate toxicity; Grade 3 = severe toxicity; Grade 4 = life-threatening or disabling toxicity, Grade 5 = death related to toxicity. Data of participants experiencing SAEs of Grade >= 3 has been presented.

Safety Population. An additional participant was randomized after the data cut-off and received pembrolizumab. Therefore, this participant was included in safety analysis.

AESI were defined as events of potential immunologic etiology, including immune-related AEs (irAEs). Severity of each AESI was reported during the study and was assigned a grade according to the NCI-CTCAE. AESIs severity were graded on a 5-point scale as: 1 = mild; discomfort noticed, but no disruption to daily activity, 2 = moderate; discomfort sufficient to reduce or affect normal daily activity, 3 = severe; inability to work or perform normal daily activity, 4 = life-threatening consequences and 5 = death related to AE. Data of participants experiencing AESIs of Grade >= 3 have been presented.

Safety Population. An additional participant was randomized after the data cut-off and received pembrolizumab. Therefore, this participant was included in safety analysis.

An AE was defined as any untoward medical occurrence in a clinical study participant, temporally associated with the use of a study intervention, whether or not considered related to the study intervention. Severity for each AE was reported during the study and assigned a grade according to the NCI-CTCAE v5.0. from Grade 1 through Grade 5. Grade 1= mild toxicity; Grade 2 = moderate toxicity; Grade 3 = severe toxicity; Grade 4 = life-threatening or disabling toxicity, Grade 5 = death related to toxicity. Data of participants experiencing AEs of Grade >= 3 have been presented. CPS was defined as the ratio of the combined number of PD-L1 expressing tumor cells and immune cells (lymphocytes and macrophages) to the total number of viable tumor cells.

Data for participants with PD-L1 CPS ≥1 in the safety population are presented. An additional participant was randomized after the data cut-off and received pembrolizumab. Therefore, this participant was included in safety analysis.

A SAE was defined as any untoward medical occurrence that, at any dose resulted in death, was life-threatening, required inpatient hospitalization or prolongation of existing hospitalization, resulted in persistent disability/incapacity, is a congenital anomaly/birth defect, any other situation such as important medical events according to medical or scientific judgement. Severity for each SAE was reported during the study and assigned a grade according to the NCI-CTCAE v5.0. from Grade 1 through Grade 5. Grade 1= mild toxicity; Grade 2 = moderate toxicity; Grade 3 = severe toxicity; Grade 4 = life-threatening or disabling toxicity, Grade 5 = death related to toxicity. Data of participants that experienced SAEs of Grade >= 3 have been presented. CPS was defined as the ratio of the combined number of PD-L1 expressing tumor cells and immune cells (lymphocytes and macrophages) to the total number of viable tumor cells.

Data for participants with PD-L1 CPS ≥1 in the safety population are presented. An additional participant was randomized after the data cut-off and received pembrolizumab. Therefore, this participant was included in safety analysis.

AESI were defined as events of potential immunologic etiology, including immune-related AEs (irAEs). Severity of each AESI was reported during the study and was assigned a grade according to the NCI-CTCAE. AESIs severity were graded on a 5-point scale as: 1 = mild; discomfort noticed, but no disruption to daily activity, 2 = moderate; discomfort sufficient to reduce or affect normal daily activity, 3 = severe; inability to work or perform normal daily activity, 4 = life-threatening consequences and 5 = death related to AE. Data of participants that experienced AESIs of Grade >= 3 have been presented.

Data for participants with PD-L1 CPS ≥1 in the safety population are presented. An additional participant was randomized after the data cut-off and received pembrolizumab. Therefore, this participant was included in safety analysis.

Number of participants with dose modifications (including dose interruptions, dose delays, dose reductions and treatment discontinuations) were reported by each interventional component.

All participants in the safety population were analyzed

Number of participants with dose modifications (including dose interruptions, dose delays, dose reductions and treatment discontinuations) were reported by each interventional component. CPS was defined as the ratio of the combined number of PD-L1 expressing tumor cells and immune cells (lymphocytes and macrophages) to the total number of viable tumor cells.

Data for participants with PD-L1 CPS ≥1 in the safety population are presented.

TTD in pain is defined as the time from randomization to the first definitive meaningful deterioration from baseline in the European Organization for Research and Treatment of Cancer Item Library(EORTC IL51) Questionnaire pain domain, i.e. an increase from baseline of at least 8.33 observed at all subsequent non-missing visits. The EORTC Quality of Life Questionnaire 35-Item Head and Neck Module (QLQ-H&N35) is a head and neck specific module with multi-item scales. The mouth pain, swallowing, speech problems, opening mouth, coughing, feeding tube, and trouble with social eating domains were administered and referred to as the EORTC IL51. The questionnaire scores for each scale and single-item measure are averaged and transformed linearly to present a score ranging from 0-100. A high score represents a high/healthy level of functioning. Kaplan-Meier estimate for the median TTD is presented, along with associated 95% confidence interval, estimated using the Brookmeyer-Crowley method.

All participants in the mITT population were analyzed

TTD in pain is defined as the time from randomization to the first definitive meaningful deterioration from baseline in the EORTC IL51 pain domain, i.e. an increase from baseline of at least 8.33 observed at all subsequent non-missing visits. The EORTC QLQ-H&N35 is a head and neck specific module with multi-item scales. The mouth pain, swallowing, speech problems, opening mouth, coughing, feeding tube, and trouble with social eating domains were administered and referred to as the EORTC IL51. The questionnaire scores for each scale and single-item measure are averaged and transformed linearly to present a score ranging from 0-100. A high score represents a high/healthy level of functioning. Kaplan-Meier estimate for the median TTD is presented, along with associated 95% confidence interval, estimated using the Brookmeyer-Crowley method. CPS was defined as the ratio of the combined number of PD-L1 expressing tumor cells and immune cells to the total number of viable tumor cells.

Data for participants with PD-L1 CPS ≥1 in the mITT population are presented.

TTD in physical function (PF) is defined as the time from randomization to the first definitive meaningful deterioration from baseline in the PF T-score, i.e. a decrease from baseline of at least 2.4 observed at all subsequent non-missing visits, as measured by the Patient-Reported Outcomes Measurement Information System - Physical Function (PROMIS PF 8c).The PROMIS PF 8c is an 8-item fixed length short form derived from the PROMIS Physical Function item bank. It includes a 5-point scale with three sets of response options. Scores on the PROMIS PF 8c are reported on a T score metric (mean = 50 and SD = 10), with higher scores reflecting better physical functioning.

All participants in the mITT population were analyzed

TTD in PF is defined as the time from randomization to the first definitive meaningful deterioration from baseline in the PF T-score, i.e. a decrease from baseline of at least 2.4 observed at all subsequent non-missing visits, as measured by the PROMIS PF 8c.The PROMIS PF 8c is an 8-item fixed length short form derived from the PROMIS Physical Function item bank. It includes a 5-point scale with three sets of response options. Scores on the PROMIS PF 8c are reported on a T score metric (mean = 50 and SD = 10), with higher scores reflecting better physical functioning. CPS was defined as the ratio of the combined number of PD-L1 expressing tumor cells and immune cells (lymphocytes and macrophages) to the total number of viable tumor cells

Data for participants with PD-L1 CPS ≥1 in the mITT population are presented.