Evaluating BL-M14D1 in Subjects With Locally Advanced or Metastatic Small Cell Lung Cancer and Neuroendocrine Tumors

Inclusion Criteria:

1. Signed the informed consent form voluntarily and agreed to follow the trialrequirements

2. Age ≥18 years

3. Subject weighs more than 40 kg

4. Has a life expectancy of ≥3 months

5. Has documented locally advanced or metastatic SCLC, large cell neuroendocrine cancer (LCNEC), neuroendocrine prostate cancer (NEPC), high-grade gastrointestinalneuroendocrine tumors (GI-NET), Merkel cell carcinoma (MCC), or other neuroendocrinetumors (with neuroendocrine histology ≥10%) who have failed at least 1 line ofstandard therapy in the advanced/metastatic setting or are unable to receivestandard treatment Notes: For SCLC, the subject must have failed at least 1 line ofplatinum therapy in the advanced/metastatic setting. No prior topoisomeraseinhibitor-based antibody-drug conjugate (ADC) therapy is permitted

6. Agree to provide archival tumor samples (FFPE tissue block or slides) from primaryor metastatic sites:

7. In dose escalation and dose finding: archival tissue obtained within 2 years orFFPE block from fresh biopsy. If no archival tissue is available, a freshtissue biopsy is required

8. In dose expansion: an FFPE block from fresh biopsy or archival tissue (within 6months) is required NOTE: If no archival tissue is available and, a freshtissue biopsy is clinically contraindicated, please consult the sponsor.

9. Has at least one measurable lesion based on RECIST (Response Evaluation Criteria inSolid Tumors) V1.1

10. Has an Eastern Cooperative Oncology Group performance status (ECOG PS) of 0 to 1

11. Toxicity of previous antitumor therapy has returned to Grade ≤1 as defined by NCICTCAE V5.0, except for alopecia and endocrinopathies controlled by replacementtherapy

12. Has no serious cardiac dysfunction and left ventricular ejection fraction ≥50%

13. Has adequate organ function, defined as:

14. Marrow function: Absolute neutrophil count (ANC) ≥1.5×109/L, platelet count ≥100×109/L, hemoglobin (Hb) ≥9.0 g/dL (blood transfusion, platelet transfusion,erythropoietin (EPO), hematopoiesis agents (such as thrombopoietin [TPO]), andG-CSF use are not allowed 1 week prior to screening)

15. Hepatic function: Total bilirubin (TBIL) ≤1.5×ULN (≤3×ULN for subjects withGilbert's syndrome or liver metastasis at baseline), AST and ALT without livermetastasis ≤3.0×ULN, AST and ALT with liver metastasis ≤5.0×ULN

16. Renal function: Creatinine (Cr) clearance ≥60 mL/minute (Cockcroft-Gaultequation)

17. Coagulation parameters: International normalized ratio (INR) ≤1.5×ULN, and activatedpartial thromboplastin time (aPTT) ≤1.5×ULN, unless receiving anticoagulationtherapy with PT and aPTT levels within the intended therapeutic range

18. Urine protein ≤2+ or ≤1000 mg/24 hours

19. Sexually active fertile subjects and their partners must agree to use highlyeffective methods of contraception (defined in Appendix D) during the course of thestudy and for 7 months after the last dose of study treatment. An additionalcontraceptive method, such as a barrier method (eg, condom), is recommended.

20. Women of childbearing potential (WOCBP) must have a negative serum pregnancy test atscreening and must be nonlactating. Female subjects are considered WOCBP unless oneof the following criteria are met: documented permanent sterilization (hysterectomy,bilateral salpingectomy, or bilateral oophorectomy) or documented postmenopausalstatus (defined as 12 months of amenorrhea in a woman >45 years old in the absenceof other biological or physiological causes. In addition, females <55 years old musthave a serum follicle stimulating hormone (FSH) level >40 mIU/mL to confirmmenopause.

Exclusion Criteria:

1. Chemotherapy, biological therapy, immunotherapy, , targeted therapy (including smallmolecule inhibitor of tyrosine kinase), and other antitumor therapy within 4 weeksor 5 half-lives (whichever is shorter) prior to the first administration; radicalradiotherapy, major surgery within 4 weeks prior to the first administration;mitomycin and nitrosoureas treatment within 6 weeks prior to the firstadministration; oral fluorouracil drugs such as tegafur, capecitabine, or palliativeradiotherapy within 2 weeks prior to initial administration.

2. Subjects who have received prior topoisomerase inhibitor-based ADC therapy

3. Concomitant use of strong inhibitors and inducers of any CYP enzyme or transportersystem within 2 weeks prior to the first administration and throughout all parts ofthe study

4. Subjects with history of severe heart disease, such as symptomatic congestive heartfailure (CHF) ≥Grade 2 (CTCAE 5.0), New York Heart Association (NYHA) ≥Grade 2 heartfailure at any time, history of myocardial infarction or unstable angina pectoriswithin 6 months before enrollment

5. Subjects with prolonged QT interval (QTcF >470 msec), complete left bundle branchblock, Grade 3 atrioventricular block, or a history of additional risk factors forTorsades de Pointes (TdP; eg, heart failure as defined in Exclusion Criterion 4,chronic or recurrent hypokalemia that requires medical intervention, congenital longQT syndrome, family history of long QT syndrome) or any current concomitantmedication known to prolong the QT/QTc interval or cause TdP

6. Active autoimmune diseases and inflammatory diseases, such as systemic lupuserythematosus, psoriasis requiring systemic treatment, rheumatoid arthritis,inflammatory bowel disease and Hashimoto's thyroiditis, etc., except for type 1diabetes, hypothyroidism that can be controlled by standard of care treatment, andskin diseases that do not require systemic treatment (such as vitiligo, psoriasis)

7. Subjects with other prior or concurrent malignancies except for basal cell carcinomaof the skin, squamous cell carcinoma of the skin and/or carcinoma in situ afteradequate resection, or other malignancy treated with curative intent with adisease-free interval of at least 3 years

8. Subjects with poorly controlled hypertension by 2 types of antihypertensive drugs (systolic blood pressure >150 mmHg or diastolic blood pressure >100 mmHg)

9. Subjects with advanced/ clinically significant lung diseases, such as poorlycontrolled COPD and asthma, restrictive lung disease, pulmonary hypertension etc.

10. Subjects who have a history of noninfectious interstitial lung disease (ILD)/pneumonitis that required treatment with steroids, have currentILD/pneumonitis, or where suspected ILD/pneumonitis cannot be ruled out by imagingat screening

11. Subjects with stroke or transient ischemic attack (TIA) within 6 months beforescreening

12. Subjects with a thromboembolic event (eg, deep vein thrombosis [DVT] or pulmonaryembolism [PE]) within 6 months before screening except for those who are clinicallystable and receiving treatment with adequate anticoagulant therapy for at least 3weeks before screening

13. Subjects with primary tumors in the central nervous system (CNS), active oruntreated CNS metastases or carcinomatous meningitis should be excluded. Patientswith previously treated brain metastases may participate provided they areclinically stable for at least 4 weeks and have no evidence of new or enlargingbrain metastases and no requirements for corticosteroids 14 days prior to screening.

14. Subjects with pre-existing Grade ≥2 peripheral neuropathy

15. Subjects who have a history of anaphylaxis or severe hypersensitivity to recombinanthumanized antibodies or human-mouse chimeric antibodies or any of the components ofBL-M14D1

16. Previous organ transplantation or allogeneic hematopoietic stem cell transplantation

17. Subjects who are receiving treatment with systemic glucocorticoids >10 mg/dayequivalent of prednisone, except for the treatment of chronic obstructive pulmonarydisease, antiemetic, infusion reactions; however, treatment with low doseglucocorticoids (≤10 mg/day equivalent of prednisone) is permitted. The use oftopical, inhaled, and locally injected steroids is permitted

18. Subjects who have received treatment with anthracyclines with a cumulative doseexceeding 360 mg/m2

19. Subjects with known human immunodeficiency virus infection (HIV Ab positive).Subjects are allowed to participate if all of the following criteria are met: (1)Undetectable HIV RNA and CD4 count ≥350 cells/μL at Screening, (2) No AIDS-definingopportunistic infection within 12 months prior to screening, (3) On stableantiretroviral therapy (ART) for at least 4 weeks prior to Screening with projectedcontinuation of ART as clinically indicated while on the study

20. Subjects with active hepatitis B virus (HBV) infection (positive HBsAg test).Subjects with chronic inactive HBV infection are eligible if they meet all of thefollowing criteria:

21. Have a HBV DNA viral load ≤ 500 IU/mL

22. Have normal AST and ALT, OR if liver metastasis is present, has AST and ALT < 3 × ULN which are not attributed to HBV infection

23. Are on antiviral treatment, as clinically indicated.

24. Subjects with active hepatitis C virus (HCV) infection (HCV antibody positive andHCV RNA > the lower limit of detection). Subjects with a positive anti-HCV antibodyare eligible only if PCR is negative for HCV RNA

25. Subjects with active or latent tuberculosis

26. Subjects with active infections requiring IV antibiotic, antiviral, or antifungaltreatment, such as severe pneumonia, bacteremia, sepsis, etc., within 1 week priorto first dose of study treatment. Subjects on stable oral antimicrobials with noclinical or laboratory evidence of active infection are eligible.

27. Participated in another clinical trial within 4 weeks prior to first dose of studytreatment

28. Subjects who are pregnant or breastfeeding, or planning to become pregnant duringthe study

29. Other conditions that the Investigator or Sponsor believes are not suitable forparticipating in this clinical trial