Inclusion Criteria:

        For Part 1A:

          -  Histologically confirmed solid tumor (cytology is allowed for NSCLC, SCLC and
             pancreatic cancer) that is metastatic or unresectable and for which there is no
             available standard therapy likely to confer clinical benefit, or patients who are 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 LS-SCLC should be
             treatment-free for at least 6 months since last chemo/radiotherapy.

          -  Has no interstitial lung disease or active, non-infectious pneumonitis.

        For Both Part 1A and Part 1B

          -  Male and female ≥ 18 years of age.

          -  Must sign an informed consent form (ICF) indicating that he or she understands the
             purpose of and procedures required for the trial and are willing to participate in the
             trial prior to any trial related assessments or procedures.

          -  ECOG performance status of 0 to 1.

          -  Measurable disease according to RECIST 1.1.

          -  Albumin level at screening ≥30 g/L.

          -  Able to receive the first administration of trial treatment within 42 days from the
             last documented disease progression.

          -  Adequate coagulation function at Screening as determined by:

               1. International normalized ratio (INR) or prothrombin time ≤1.5 x upper limit
                  normal (ULN; unless on therapeutic anticoagulants with values within therapeutic
                  window),

               2. 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:

               1. White blood count (WBC) ≥3 x 10^9/L

               2. Absolute neutrophil count (ANC) ≥1.5 x 10^9/L (patient may not use
                  granulocyte-colony stimulating factor (G-CSF) or granulocyte-macrophage colony
                  stimulating factor (GM-CSF) to achieve these WBC and ANC levels),

               3. Platelet count ≥100 x 10^9/L,

               4. Hemoglobin (Hgb) ≥9.0 g/dL (may not transfuse or use erythropoietin to obtain
                  this Hgb level).

          -  Adequate hepatic function at Screening as determined by:

               1. Total bilirubin ≤ 1.5 mg/dL (or ≤ 2.0 mg/dL for patients with known Gilbert's
                  syndrome),

               2. 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 m²- 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, is expressed in
             mg/dL; multiplied by 0.742 if the patient is female; multiplied by 1.212, if the
             patient is African-American (Levey et al., 1999).

          -  Able to attend trial visits as required by the protocol.

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

          -  WOCBP must agree 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 is sexually active with a woman of childbearing potential and has not had a
             vasectomy must agree 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 provide an FFPE (Formalin Fixed Paraffin Embedded) from the latest
             available archival tumor tissue. If such tissue cannot be provided, the sponsor's
             approval of enrollment is needed.

        Exclusion Criteria:

        Prior and Concomitant Therapy:

          -  Has received prior systemic therapy with a TLR7 agonist.

          -  Has been receiving: radiotherapy, chemotherapy, or molecularly-targeted agents or
             tyrosine kinase inhibitors within 2 weeks or 5 half-lives (whichever is longer) of the
             start of trial treatment; immunotherapy/monoclonal antibodies within 3 weeks of the
             start of trial treatment; any live vaccine within 4 weeks of the start of trial
             treatment; nitrosoureas, antibody-drug conjugates, or radioactive isotopes within 6
             weeks of the start of trial treatment.

          -  Receives concurrent systemic (oral or intravenous) steroid therapy >10 mg prednisone
             daily or its equivalent for an underlying condition.

          -  Receives concurrent strong inhibitors or inducers of the cytochrome P450 enzymes.

          -  Has had major surgery within the 4 weeks before the first dose of BNT411.

          -  Has ongoing or active infection requiring intravenous treatment with anti-infective
             therapy that has been administered less than two weeks prior to first dose of trial
             treatment.

          -  Has side effects of any prior therapy or procedures for any medical condition not
             recovered to NCI CTCAE v.5 grade ≤1.

          -  Has any contraindication to atezolizumab, carboplatin or etoposide as per USPI or SmPC
             in Part 1B.

        Medical Conditions

          -  Current evidence of new or growing brain or leptomeningeal metastases during
             screening. Patients with known brain or leptomeningeal metastases may be eligible if
             they:

               1. had radiotherapy, surgery or stereotactic surgery for the brain or leptomeningeal
                  metastases,

               2. have no neurological symptoms (excluding Grade ≤2 neuropathy),

               3. have stable brain or leptomeningeal disease on the CT or MRI scan within 4 weeks
                  before signing the informed consent,

               4. are not undergoing acute corticosteroid therapy or steroid taper.

          -  Has history of seizures other than isolated febrile seizure in childhood; has a
             history of a cerebrovascular accident or transient ischemic attack less than 6 months
             ago.

          -  Has effusions (pleural, pericardial, or ascites) requiring drainage.

          -  Has eye pathology likely to confound observation of potential ocular AEs.

          -  Has a fever ≥38°C within 3 days before signing the ICF.

          -  Has a history of autoimmune disease active or past including but not limited to
             inflammatory bowel disease, systemic lupus erythematosus (SLE), ankylosing
             spondylitis, scleroderma, or multiple sclerosis. Has any active immunologic disorder
             requiring immunosuppression with steroids or other immunosuppressive agents (e.g.,
             azathioprine, cyclosporine A) with the exception of patients with isolated vitiligo,
             resolved childhood asthma or atopic dermatitis, controlled hypoadrenalism or
             hypopituitarism, and euthyroid patients with a history of Grave's disease. Patients
             with controlled hyperthyroidism must be negative for thyroglobulin, thyroid peroxidase
             antibodies, and thyroid-stimulating immunoglobulin prior to trial drug administration.

          -  Known history of seropositivity for human immunodeficiency virus (HIV) with CD4+
             T-cell (CD4+) counts <350 cells/uL and with a history of acquired immunodeficiency
             syndrome (AIDS)-defining opportunistic infections.

          -  Known history/positive serology for hepatitis B requiring active anti-viral therapy
             (unless immune due to vaccination or resolved natural infection or unless passive
             immunization due to immunoglobulin therapy). Patients with positive serology must have
             Hepatitis B virus (HBV) viral load below the limit of quantification.

          -  Active Hepatitis C virus (HCV) infection; patients who have completed curative
             antiviral treatment with HCV viral load below the limit of quantification are allowed.

          -  Has a known hypersensitivity to a component of BNT411 drug product, or another similar
             compound.

          -  Has another primary malignancy that has not been in remission for at least 2 years,
             with the exception of those with a negligible risk of metastasis or death (such as
             adequately treated carcinoma in situ of the cervix, basal or squamous cell skin
             cancer, localized prostate cancer, or ductal carcinoma in situ).

        Other Comorbidities

          -  Has abnormal electrocardiograms (ECGs) that are clinically significant, such as
             Framingham-corrected QT interval >480 ms.

          -  In the opinion of the treating investigator, has any concurrent conditions that could
             pose an undue medical hazard or interfere with the interpretation of the trial
             results; these conditions include, but are not limited to:

               1. ongoing or active infection requiring antibiotic/antiviral/antifungal therapy,

               2. concurrent congestive heart failure (New York Heart Association [NYHA] Functional
                  Classification Class III or IV),

               3. concurrent unstable angina,

               4. concurrent cardiac arrhythmia requiring treatment (excluding asymptomatic atrial
                  fibrillation),

               5. acute coronary syndrome within the previous 6 months,

               6. significant pulmonary disease (shortness of breath at rest or on mild exertion)
                  for example due concurrent severe obstructive pulmonary disease.

          -  Has a cognitive, psychological or psychosocial impediment that would impair the
             ability of the patient to receive therapy according to the protocol or adversely
             affect the ability of the patient to comply with the informed consent process,
             protocol, or protocol-required visits and procedures.

          -  Is pregnant or breastfeeding.