Study of Avelumab-M3814 Combinations

Inclusion Criteria:

* Part A and Part FE (M3814 + avelumab): Participants had histologically or cytologically proven advanced or metastatic solid tumors for which no standard therapy exists, standard therapy has failed, or participants are intolerant to or have rejected established therapy known to provide clinical benefit for their condition
* Part B (M3814 + Radiotherapy \[RT\] + avelumab): histologically or cytologically proven advanced or metastatic solid tumors for which no standard therapy exists, standard therapy has failed, or participants are intolerant to or have rejected established therapy known to provide benefit for their condition and are amenable to receive RT
* Part A, B and FE: Measurable or evaluable disease according to Response Evaluation Criteria in Solid Tumors Version 1.1 (RECIST v 1.1)
* Eastern Cooperative Oncology Group performance status (ECOG PS) of 0 to 1 at study entry
* Part A, B and FE: Female participants of childbearing potential should be willing to use a highly effective contraceptive method
* Part A, B and FE: Male participants should agree to refrain from donating sperm plus, either: abstain from any activity that allows for exposure to ejaculate
* Use an adequate method of contraception starting with the first dose of study therapy through 90 days after the last dose of study therapy
* Part A, B and FE: Be willing to provide informed consent for the trial
* Other protocol defined inclusion criteria could apply

Exclusion Criteria:

* Participants who had received prior chemotherapy, hormonal anticancer therapy with the exception of luteinizing hormone-releasing hormone analogs, biologic therapy, or any other anticancer therapy within 28 days of the first dose of study treatments (6 weeks for nitrosoureas or mitomycin C)
* Participants who had undergone major surgery for any reason, except diagnostic biopsy, within 4 weeks of the study intervention and/or has not fully recovered from the surgery within 4 weeks of the study intervention
* Participants with evidence of active or history of autoimmune disease that might deteriorate when receiving an immune-stimulatory agent
* Participants with brain metastases, except those meeting the following criteria: a) brain metastases that have been treated locally and are clinically stable for greater than or equal to (\>=) 4 weeks prior to randomization b) no ongoing neurological symptoms that are related to the brain localization of the disease (sequelae that are a consequence of the treatment of the brain metastases are acceptable) c) participants must be either off steroids or on a stable or decreasing dose of less than (\<) 10 milligrams (mg) daily prednisone (or equivalent)
* Participants with severe acute or chronic medical conditions including immune colitis, inflammatory bowel disease, immune pneumonitis, pulmonary fibrosis or psychiatric conditions including recent (within the past year), psychiatric or substance abuse disorders; or active suicidal ideation or behavior; or laboratory abnormalities that may increase the risk associated with study participation or study intervention administration or may interfere with the interpretation of study results
* Participants requiring systemic immunosuppressive agents (such as steroids) for any reason who cannot be tapered off these drugs before start of study intervention, with the following exceptions: a) participants with adrenal insufficiency, may continue corticosteroids at physiologic replacement dose, equivalent to less than or equal to (\<=) 10 mg prednisone daily b) participants requiring steroids through a route known to result in a minimal systemic exposure (topical, intranasal, intra-ocular, or inhalation) is permitted c) participants with previous or ongoing administration of systemic steroids for the management of an acute allergic phenomenon planned to be completed in 14 days, or that the dose after 14 days will be equivalent to \<= 10 mg prednisone daily
* Participants with a history of human immunodeficiency virus (HIV) or known acquired immunodeficiency syndrome, Hepatitis B virus or Hepatitis C and with history of infection must have a polymerase chain reaction (PCR) documentation that infection is cleared
* Participants who had received a live vaccine within 30 days prior to the first dose of trial treatment
* Participants with known prior severe hypersensitivity to any of the investigational products or any component in its formulations
* Participants with evidence of additional malignancy within the last 5 years unless a complete remission without further recurrence was achieved at least 2 years prior to study entry and participants were deemed to have been cured with no additional therapy required or anticipated to be required. Participants with treated nonmelanoma skin cancers, carcinoma in situ of skin, bladder, cervix, colon/rectum, breast, or prostate may participate
* Participants pretreated with immunotherapy who have, any history of dose limiting toxicities (DLTs) with prior immunotherapy agents, including Grade 3/4 immune-related adverse events (irAEs); irreversible irAEs; Grade greater than or equals to (\>=) 3 irAEs that did not respond to steroid rescue; or neurologic irAE with significant clinical sequelae
* Participants with irAE requiring hormone replacement therapy (e.g., thyroxine, insulin, or physiologic dose of corticosteroid replacement therapy for adrenal or pituitary insufficiency) may participate as long as the endocrinopathy is well controlled and the participant is not otherwise symptomatic from hormone insufficiency
* Physiologic corticosteroid dose is defined as \<= 10 mg daily of prednisone or equivalent
* for Part B only:
* Participants who had confirmed esophagitis and in whom radiation planning target volume will include any portion of the esophagus, the participant is not eligible unless an esophageal endoscopy rules out the presence of esophagitis
* Participants in whom more than 10 percent (%) of the total esophagus volume might receive more than 15 gray (Gy) (50% of the prescribed radiotherapy \[RT\] dose)
* Participants who have had previous radiotherapy to the same region as intended to be irradiated in this study within the past 12 months
* Participants who had had extensive previous radiotherapy on \>= 30% of bone marrow reserve or prior bone marrow/stem cell transplantation within 5 years before study start
* If participant hepatic metastatic lesion is selected to be irradiated: - the non-tumor liver volume \< 700 milli liters (mL); - Child-Pugh score \>= 8
* Other protocol defined exclusion criteria could apply