Inclusion Criteria:

          -  Capable of giving signed informed consent/assent which includes compliance with the
             requirements and restrictions listed in the informed consent form (ICF) and protocol.

          -  Male or female, aged 18 years or older.

          -  Body weight >=30 kilograms (kg).

          -  Histological or cytological documentation of an invasive malignancy that was diagnosed
             as locally advanced/metastatic or relapsed/refractory and is of one of the following
             tumor types: a) Part 1: cutaneous melanoma; HNSCC (oral cavity, larynx, oropharynx,
             hypopharynx, nasal cavity/paranasal sinuses); non-small cell lung cancer (squamous and
             non-squamous); urothelial carcinoma of the upper and lower urinary tract; clear cell
             renal carcinoma; castrate resistant prostate adenocarcinoma. b) Part 2: HNSCC (oral
             cavity, larynx, pharynx, paranasal sinuses).

          -  Part 1 only: Disease that has progressed after standard therapy for the specific tumor
             type, or for which standard therapy has proven to be ineffective, intolerable, or is
             considered inappropriate, or if no further standard therapy exists, or where standard
             therapy is refused. May be anti-PD-1/anti-PD-L1 experienced or naïve.

          -  Part 2 only: Disease that has progressed after receiving platinum-based chemotherapy
             (unless medically contraindicated or discontinued due to toxicity) and
             anti-PD-1/anti-PD-L1 therapy (in combination or as separate lines of therapy in either
             sequence).

          -  Measurable disease per RECIST version 1.1 guidelines. Palpable lesions that are not
             measurable by radiographic or photographic evaluations may not be utilized as the only
             measurable lesion. Any measurable lesion biopsied at Screening cannot be followed as a
             target/index lesion unless agreed upon by GlaxoSmithKline (GSK).

          -  Eastern Cooperative Oncology Group (ECOG) Performance Status (PS) score of 0 or 1.

          -  Adequate organ function.

          -  A female subject is eligible to participate if she is not pregnant, not breastfeeding,
             and at least one of the following conditions apply: a) Not a woman of childbearing
             potential (WOCBP); or, b) A WOCBP who agrees to follow the contraceptive while
             receiving study intervention and for at least 180 days after the last dose of study
             intervention.

          -  A male subject must agree to use a highly effective contraception while receiving
             study intervention and for at least 180 days after the last dose of study intervention
             and refrain from donating sperm during this period.

          -  Agree to collection of tumor tissue: a) Part 1 and Part 2: Archival tumor tissue
             collected any time from the initial diagnosis of invasive malignancy; a fresh tumor
             biopsy will be required if archival specimen is unavailable prior to first dose. b)
             Part 1 pharmacokinetic/pharmacodynamic cohort(s): Archival tissue as noted in point
             (a) above. Paired tumor biopsies: tumor tissue collected any time after completion of
             dosing of the last therapy and prior to first dose and an on-treatment biopsy. c) Part
             2: A minimum of 15 subjects from each arm will be required to provide paired tumor
             biopsies (in addition to the archival tissues as noted in point (a) above): tumor
             tissue collected any time after completion of dosing of the last therapy and prior to
             first dose and an on-treatment biopsy.

        Exclusion Criteria:

          -  Received prior treatment with the following therapies; calculation is based on date of
             last therapy to date of first dose of study intervention or SOC: a) Cytotoxic
             T-Lymphocyte-Associated Protein 4 (CTLA-4 [including tremelimumab] or Inducible T Cell
             Co-Stimulator (ICOS)-directed therapies at any time; b) >=4 lines of prior anticancer
             treatment: In subjects that relapse or progress within 1 year from the beginning of
             adjuvant or concurrent therapy, the adjuvant/concurrent therapy is considered first
             line therapy; c) Systemic anticancer therapy or investigational therapy within 30
             days, or 5 half-lives, whichever is shorter; at least 14 days must have elapsed
             between the date of the last prior therapy to the date of first dose of study
             intervention or SOC.

          -  Prior radiation therapy: permissible if at least one non-irradiated measurable lesion
             is available for assessment per RECIST v1.1 or if a solitary measurable lesion was
             irradiated, objective progression is documented. At least 14 days must have elapsed
             between the date of the last dosage of radiation and the first dose of study
             intervention/SOC.

          -  Invasive malignancy or history of invasive malignancy other than disease under study
             within the last two years, except: a) Any other invasive malignancy for which the
             subject was definitively treated, has been disease-free for <=2 years and in the
             opinion of the Investigator and Medical Monitor will not affect the evaluation of the
             effects of the study intervention or SOC on the currently targeted malignancy, may be
             included in this clinical study; Curatively treated non-melanoma skin cancer or
             successfully treated in-situ carcinoma.

          -  Toxicity from previous anticancer treatment that includes: a) >=Grade 3 toxicity
             considered related to prior immunotherapy and that led to treatment discontinuation;
             b) Toxicity related to prior treatment that has not resolved to <=Grade 1 (except
             alopecia, vitiligo, hearing loss, endocrinopathy managed with replacement therapy, and
             peripheral neuropathy which must be <=Grade 2).

          -  Central nervous system (CNS) metastases, with the following exception: Subjects with
             previously treated CNS metastases who are clinically stable and had no requirement for
             steroids during at least 14 days prior to first dose of study intervention or SOC.

          -  Major surgery <=28 days of first dose of study intervention or SOC.

          -  Autoimmune disease (current or history) or syndrome that required systemic treatment
             within the past 2 years. Replacement therapies which include physiological doses of
             corticosteroids for treatment of endocrinopathies (i.e., adrenal insufficiency) are
             not considered systemic treatments.

          -  Recent history (within 24 weeks) of gastrointestinal obstruction that required
             surgery, acute diverticulitis, inflammatory bowel disease, or intra-abdominal abscess.

          -  Receiving systemic steroids (>=10 milligrams [mg] oral prednisone or equivalent) or
             other immunosuppressive agents within 7 days prior to first dose of study intervention
             or SOC.

          -  Prior allogeneic/autologous bone marrow or solid organ transplantation.

          -  Received live-virus vaccine within 30 days from start of study intervention or SOC.

          -  Current or history of idiopathic pulmonary fibrosis, pneumonitis (for past, subject is
             excluded if steroids were required), interstitial lung disease or organizing
             pneumonia.

          -  Recent history (within 24 weeks) of uncontrolled, symptomatic ascites, pleural or
             pericardial effusions.

          -  History or evidence of cardiac abnormalities within the 24 weeks prior to enrollment
             which include: a) Serious uncontrolled cardiac arrhythmia or clinically significant
             electrocardiogram abnormalities including second degree (Type II) or third degree
             atrioventricular block. b) Cardiomyopathy, myocardial infarction, acute coronary
             syndromes (including unstable angina pectoris), coronary angioplasty, stenting, or
             bypass grafting. c) Symptomatic pericarditis.

          -  Current unstable liver or biliary disease per Investigator assessment defined by the
             presence of ascites, encephalopathy, coagulopathy, hypoalbuminemia, esophageal or
             gastric varices, persistent jaundice, or cirrhosis.

          -  Active infection requiring systemic therapy.

          -  Known human immunodeficiency virus infection; positive test for hepatitis B active
             infection (presence of hepatitis B surface antigen) or hepatitis C active infection.

          -  History of severe hypersensitivity to monoclonal antibodies, the Standard of Care
             agents, including any ingredient used in the formulation, based on which treatment the
             subject is to receive.

          -  Any serious and/or unstable pre-existing medical (aside from malignancy), psychiatric
             disorder, or other conditions that could interfere with subject's safety, obtaining
             informed consent or compliance to the study procedures, in the opinion of the
             Investigator.

          -  For subjects receiving SOC: Requires therapy with a medication that may alter the PK
             of the SOC agent (e.g., strong inducers or inhibitors of cytochrome P (CYP)3A4 for
             subjects receiving docetaxel or paclitaxel) during the study treatment period. Please
             refer to the package insert for the agent the subject is to receive.

          -  For subjects receiving SOC: Any contraindication, per the package insert and/or
             Institutional guidelines, to the treatment the subject is to receive.