Study of MK-4280 as Monotherapy and in Combination With Pembrolizumab (MK-3475) With or Without Chemotherapy AND MK-4280A as Monotherapy in Adults With Advanced Solid Tumors (MK-4280-001)

Inclusion Criteria:

- Part A and Part B: Has histologically or cytologically-confirmed metastatic solid
tumor.

- Has measurable disease by immune-related Response Evaluation Criteria in Solid Tumors
(irRECIST) 1.1 criteria.

- Has a performance status of 0 or 1 on the Eastern Cooperative Oncology Group (ECOG)
Performance Scale.

- Demonstrates adequate organ function

- If female of child-bearing potential, is willing to use an adequate method of
contraception for the course of the study through 120 days after the last dose of
study drug.

- If male with a female partner(s) of child-bearing potential, must agree to use an
adequate method of contraception starting with the first dose of study drug through
120 days after the last dose of study drug. Males with pregnant partners must agree to
use a condom; no additional method of contraception is required for the pregnant
partner.

Exclusion Criteria:

- Has had chemotherapy, radiation or biological cancer therapy within 4 weeks prior to
the first dose of study drug, or has not recovered to Common Terminology Criteria for
Adverse Events (CTCAE) Grade 0 or 1 from the AEs due to cancer therapeutics
administered more than 4 weeks earlier (this includes participants with previous
immunomodulatory therapy with residual immune-related [ir]AEs).

- Is currently participating and receiving study therapy or has participated in a study
of an investigational agent and received study therapy or used an investigational
device within 4 weeks of the first dose of study drug.

- Has received previous treatment with another agent targeting the lymphocyte-activation
gene 3 (LAG-3) receptor.

- Has received previous treatment with an immunomodulatory therapy (e.g. anti-programmed
cell death-1/anti-programmed cell death-ligand 1 [anti-PD-1/anti-PD-L1] or cytotoxic
T-lymphocyte-associated protein 4 [CTLA 4] agent) and was discontinued from that
therapy due to a Grade 3 or higher irAE.

- Is expected to require any other form of antineoplastic therapy while on study.

- Has a diagnosis of immunodeficiency or is receiving chronic systemic steroid therapy
in excess of replacement doses, or on any other form of immunosuppressive medication.

- Has a history of a previous, additional malignancy, unless potentially curative
treatment has been completed, with no evidence of malignancy for 5 years. Time frame
exceptions include successful definitive resection of basal cell carcinoma of the
skin, superficial bladder cancer or in situ cervical cancer, or other in situ cancers.

- Has known active central nervous system (CNS) metastases and/or carcinomatous
meningitis.

- Has had a severe hypersensitivity reaction to treatment with another monoclonal
antibody.

- Has an active autoimmune disease or a documented history of autoimmune disease, except
vitiligo or resolved childhood asthma/atopy.

- Has an active infection requiring therapy.

- Has history of (non-infectious) pneumonitis that required steroids or has current
pneumonitis.

- Has had a prior stem cell or bone marrow transplant.

- Has a known history of or screens positive for Human Immunodeficiency Virus (HIV),
active chronic or acute Hepatitis B or Hepatitis C.

- Has known psychiatric or substance abuse disorders that would interfere with
cooperation with the requirements of the study.

- Is a regular user as determined by investigator judgment (including "recreational
use") of any illicit drugs or has a recent history (within the last year) of substance
abuse (including alcohol), at the time of signing informed consent.

- Has symptomatic ascites or pleural effusion. A participant who is clinically stable
following treatment for these conditions (including therapeutic thoraco- or
paracentesis) is eligible.

- Is pregnant or breastfeeding, or expecting to conceive or father children within the
projected duration of the study, starting with the screening visit through 120 days
after the last dose of study drug.

- Has clinically significant heart disease that affects normal activities.

- Has had major surgery in the past 4 weeks.

- Has received a live-virus vaccine within 30 days of planned start of study drug.
Seasonal flu vaccines that do not contain live virus are permitted.