Nelmastobart（hSTC810） is a novel humanized monoclonal antibody that fuses on IgG4 and targets a novel immune checkpoint protein, BTN1A1+.This is an phase Ib bridging trial conducted in China to assess the safety, tolerability, and pharmacokinetic characteristics of Nelmastobart in combined with TAS-102 and Bevacizumab in Chinese participants with mCRC, and to verify that the safety results align with those from the Korean STCUBE-003 phase Ib trial. The phase Ib trial will also provide supportive data for conducting a randomized, double-blind, controlled Phase II study in China.

Inclusion Criteria:

• Participants who participate in the study must meet all of the following inclusion criteria.

  1. Adults ≥18 years old and of any gender when signing the informed consent form.

  2. Participants with metastatic/recurrent colorectal cancer confirmed by histopathology/cytology who have not responded to or are unable to receive standard anti-cancer therapy based on oxaliplatin and irinotecan. Participants who undergo curative surgery for colorectal cancer and receive adjuvant anti-cancer therapy will be considered to have received their first palliative anti-cancer therapy if their disease recurs during or within 6 months after completion of the adjuvant anti-cancer treatment.

  3. According to the Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1, there must be at least one measurable or assessable lesion present.

  4. Participants with ECOG performance status 0-1

  5. Participants with adequate bone marrow and body organ functions

     1. Absolute neutrophil count (ANC) ≥ 2.0 x 109/L
     2. Hemoglobin count (Hgb) ≥ 9.0 g/dL
     3. Platelet count ≥ 100 x 109/L
     4. Serum creatinine ≤ ULN x 1.5 or serum creatinine clearance > 30mL/min
     5. Total bilirubin ≤ 1.5 x ULN (Participants with biliary obstruction may be enrolled if they meet the criterion after adequate biliary drainage.)
     6. AST and ALT ≤ 3 x ULN in the absence of liver metastasis;
     7. or AST and ALT ≤ 5 x ULN in the presence of liver metastasis

  6. Confirm that participants with adequate cardiac function at the screening visit QTc calculated using the Fredericia formula ≤ 480 msec (Those with QTc >480 msec may be enrolled if the mean of 3 consecutive QTc measurements is <480 msec.).

  7. A negative serum β-HCG test within 14 days prior to IP dosing for women of childbearing potential

  8. Participants who agree, and are able to use during the study medically reliable methods of contraception as follows:

     To be eligible for enrollment, women of childbearing potential (all women who can have physiological pregnancy during IP treatment and for 6 months after the end of IP treatment unless they use appropriate methods of contraception) must use the following methods of contraception.

     1. Participants must refrain from any type of sexual intercourse, and persistent abstinence in daily life is recommended. Periodic abstinence (e.g., rhythm method, cervical mucus method, basal body temperature method, etc.) and withdrawal method are not acceptable methods of contraception.
     2. Female sterilization procedures: Bilateral ovariectomy with or without hysterectomy; tubal ligation within 6 weeks prior to enrollment in this study. If the subject is confirmed to have childbearing potential based on the assessment of hormone level, only bilateral ovariectomy will be permitted.
     3. Vasectomized partner (at least 6 months prior to screening). For women who participate in the study, the vasectomized partner must be the only partner during her participation in this study.
     4. Men must use condoms during sexual intercourse during and after IP treatment (for 6 months after the last IP dose).

  9. Life expectancy ≥3 months

  10. Participants who consent to sampling tumor tissues or collecting tumor tissue samples obtained within 2 years prior to the screening visit.

  11. Participants who, after being fully informed of the study, voluntarily decide to participate in the study, provide written informed consent, and agree to comply with study procedures during the study.

Exclusion Criteria:

• Participants who meet any of the following exclusion criteria will be excluded from the study.

  1. Participants who have hypersensitivity to the active ingredient of IP or any of its components (excipients)

  2. Participants who had cytotoxic chemotherapy within 14 days prior to randomization; treatment with IP in another clinical trial with the elapse of ≤2 weeks from the last dose of that IP or ≤5 folds the half-life of that IP; or treatment with monoclonal antibody therapy within the past 4 weeks

  3. Uncontrolled serious infection

  4. Confirmed PD during treatment with trifluridine/tipiracil for palliative care or confirmed recurrence within 6 months after the end of such treatment

  5. Participants requiring high-dose steroids (>10 mg/day prednisone or equivalent) or other immunosuppressants However, these participants may be enrolled in the following cases.

     1. Short-term (<7 days) use of systemic corticosteroids that are considered standard of care will be allowed.
     2. Participants requiring intermittent use of bronchodilators, inhalant steroids, or local steroid injections will be allowed.
     3. Replacement therapy (e.g., thyroxine, insulin, physiological corticosteroid replacement therapy for adrenal or pituitary insufficiency) is not considered as a type of systemic treatment and will be allowed.

  6. Pregnant or lactating women

  7. Participants with a history of autoimmune disease requiring systemic treatment (i.e., use of disease modifying therapy, corticosteroids, or immunosuppressants) within 2 years prior to the screening visit (However, enrollment will be possible for subjects with vitiligo, psoriasis not requiring systemic treatment, type 1 diabetes mellitus, hypothyroidism stably managed with hormone replacement therapy, Sjogren's syndrome, or resolved pediatric asthma/atopy.)

  8. Participants with active central nervous system lesions (radiologically unstable or symptomatic brain lesions). With the exception of patients with meningeal metastasis, individuals who had radiotherapy or surgical treatment may be enrolled if there is evidence that the patient's condition is maintained without steroid therapy and that the disease of the brain lesion has not progressed for ≥4 weeks.

  9. Participants with a documented history of cerebrovascular events (stroke or transient ischemic attack), unstable angina pectoris, myocardial infarction, or cardiac symptoms consistent with New York Heart Association (NYHA) Class IV within 6 months prior to the screening visit

  10. Participants with hypertensive encephalopathy or hypertension that is not adequately controlled with antihypertensives

  11. Participants with a history of idiopathic pulmonary fibrosis, organizing pneumonia, drug-induced pneumonitis, or idiopathic pneumonia; or with active pneumonia based on screening chest X-rays

  12. Participants who received allogeneic stem cell or solid organ transplants

  13. Participants who received live attenuated vaccines within 30 days prior to the screening visit. Examples of live vaccines include, but are not limited to measles, mumps, rubella, varicella/(varicella) zoster, yellow fever, rabies, bacillus Calmette-Guerin, and typhoid vaccines. Injectable seasonal influenza vaccines are generally killed virus vaccines and will be allowed. However, intranasal influenza vaccines are live attenuated vaccines and will not be allowed.

  14. Participants with a history of other primary cancers However, enrollment will be possible for the following cancers.

      1. Adequately treated skin cancer (basal cell or squamous carcinoma) that is not melanoma, superficial cervical cancer or stage 1 bladder cancer, completely resected thyroid cancer which did not metastasize and for which all treatment is completed (Scars must have been adequately treated prior to study enrollment).
      2. Treated solid tumor with no evidence of recurrent disease at least 36 months prior to screening

  15. Side effects of prior anticancer therapy that did not recover to Grade ≤1 (with the exception of alopecia)

  16. Participants who had radiotherapy in an extensive lesion involving ≥30 % of the bone marrow within 4 weeks prior to the screening visit or limited range radiotherapy for palliative care within 2 weeks

  17. Participants who had major surgery within 4 weeks prior to the screening visit or who have not recovered from side effects of surgery

  18. Participants who are unable to take drugs orally or who have a past history, or pathological findings of major gastrointestinal surgery that may affect the absorption of IP

  19. Participants who have evidence of active infection including hepatitis B, hepatitis C, and human immunodeficiency virus (HIV) However, enrollment will be possible for the following cases.

  20. Participants with positive hepatitis B surface antigen (HBsAg) may be enrolled if HBV DNA is negative based on a local test.

      1. Participants with positive hepatitis B core antibody (IgG anti-HBc) and a history of HBV infection may be enrolled if HBV DNA is negative.
      2. Participants with positive anti-HCV Ab may be enrolled if HCV RNA is negative.
      3. Participants with hereditary problems such as galactose intolerance, Lapp lactase deficiency, or glucose-galactose malabsorption

  21. Participants with medical, psychiatric, or cognitive disorders or impaired ability to understand information, provide prior consent, comply with protocol procedures, or complete the study

  22. Those whom the investigator deems inappropriate for participation in this clinical trial