∙ For Part 1A:

• Histologically confirmed solid tumor (cytology was allowed for non-small cell lung cancer \[NSCLC\], small cell lung cancer \[SCLC\] and pancreatic cancer) that was metastatic or unresectable and for which there was no available standard therapy likely to confer clinical benefit, or patients who were not candidates for such available therapy.

∙ For Part 1B:

• Histologically or cytologically confirmed ES-SCLC (per the Veterans Administration Lung Study Group \[VALG\] staging system) who received no prior chemotherapy for extensive stage disease.

• Those treated with prior chemo/radiotherapy with curative intent for limited-stage small cell lung cancer (LS-SCLC) were treatment-free for at least 6 months since last chemo/radiotherapy.

• Did not have interstitial lung disease or active, non-infectious pneumonitis.

∙ For Both Part 1A and Part 1B:

• Male and female \>= 18 years of age.

• Must have signed an informed consent form (ICF) indicating that he or she understood the purpose of and procedures required for the trial and were willing to participate in the trial prior to any trial-related assessments or procedures.

• Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 1.

• Measurable disease according to RECIST 1.1.

• Albumin level at screening \>= 30 g/L.

• Adequate coagulation function at screening as determined by:

‣ International normalized ratio (INR) or prothrombin time \<= 1.5 x upper limit normal (ULN; unless on therapeutic anticoagulants with values within therapeutic window),

⁃ Activated partial thromboplastin time (aPTT) \<= 1.5 x ULN (unless on therapeutic anticoagulants with values within therapeutic window).

• Adequate hematologic function at screening as determined by:

‣ White blood cell count (WBC) \>= 3 x 10\^9/L,

⁃ Absolute neutrophil count (ANC) \>= 1.5 x 10\^9/L (patient could not use granulocyte-colony stimulating factor (G-CSF) or granulocyte-macrophage colony stimulating factor (GM-CSF) to achieve these WBC and ANC levels),

⁃ Platelet count \>= 100 x 10\^9/L,

⁃ Hemoglobin (Hgb) \>= 9.0 g/dL.

• Adequate hepatic function at screening as determined by:

‣ Total bilirubin \<= 1.5 mg/dL (or \<= 2.0 mg/dL for patients with known Gilbert's syndrome),

⁃ Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) \<= 2.5 x ULN; or \<= 5 x ULN in patients with metastatic liver disease.

• Adequate renal function at screening as determined by:

• a. Glomerular filtration rate (GFR) \>= 60 mL/min/1.73 m\^2 - e.g., according to the abbreviated Modification of Diet in Renal Disease (MDRD) equation: GFR = 186 × (SCr\^-1.154) × (age\^-0.203) (where SCr, the serum creatinine level, was expressed in mg/dL; multiplied by 0.742 if the patient was female; multiplied by 1.212, if the patient was African-American (Levey et al., 1999).

• Were able to attend trial visits as required by the protocol.

• Women of childbearing potential (WOCBP) must have had a negative serum (beta-human chorionic gonadotropin \[beta-hCG\]) test/value at screening. Patients who were postmenopausal or permanently sterilized were considered as not having reproductive potential.

• WOCBP must have agreed not to donate eggs (ova, oocytes) for the purposes of assisted reproduction during the entire trial, until 6 months after last BNT411 treatment.

• A man who was sexually active with a WOCBP and had not had a vasectomy must have agreed to use a barrier method of birth control, e.g., either condom with spermicidal foam/gel/film/cream/suppository or partner with occlusive cap (diaphragm or cervical/vault caps) with spermicidal foam/gel/film/cream/suppository, and all men must also not donate sperm during the trial and for 6 months after receiving the last dose of BNT411.

• All patients must have provided a Formalin Fixed Paraffin Embedded (FFPE) sample from the latest available archival tumor tissue. If such tissue was not provided, the sponsor's approval of enrollment was needed.