A Study of XmAb®20717 in Subjects With Selected Advanced Solid Tumors

Inclusion Criteria:

- Histologically or cytologically confirmed diagnosis of advanced solid tumors
including:

- Melanoma;

- Breast carcinoma that is estrogen receptor, progesterone receptor, and Her2
negative (triple-negative breast cancer; TNBC);

- Hepatocellular carcinoma;

- Urothelial carcinoma;

- Squamous cell carcinoma of the head and neck;

- Renal cell carcinoma (clear cell predominant type);

- Microsatellite instability-high or mismatch repair deficient colorectal carcinoma
or endometrial carcinoma;

- Non-small cell lung carcinoma;

- Gastric or gastroesophageal junction adenocarcinoma

- Mesothelioma;

- High-grade neuroendocrine carcinoma, including small cell carcinoma of the lung

- Cervical cancer;

- Squamous cell carcinoma of the anus

- All subjects' cancer must have progressed after treatment with standard therapies or
have no appropriate available therapies.

- Have available adequate archival formalin-fixed paraffin-embedded block(s)/slides
containing tumor or adequate pre-dose fresh tumor biopsy tissue

- Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1

Exclusion Criteria:

- Treatment with any CTLA4 antibody within 6 weeks of the start of study drug.

- Treatment with nivolumab or any PDL1 or PDL2-directed antibody within 4 weeks of the
start of study drug.

- Treatment with pembrolizumab within 4 - 12 weeks of the start of study drug (cohort
dependent).

- Subjects currently receiving other anticancer therapies.

- Treatment with any other anticancer therapy within 2 weeks of the start of study drug
(i.e., other immunotherapy, chemotherapy, radiation therapy, etc.).

- A life-threatening (Grade 4) immune-mediated adverse event related to prior
immunotherapy.

- Failure to recover from any immune-related toxicity from prior cancer therapy to ≤
Grade 1, except if previous immune-related endocrinopathy is medically managed with
hormone replacement therapy only.

- Failure to recover from any other toxicity (other than immune-related toxicity)
related to previous anticancer treatment to ≤ Grade 2.

- Have known active CNS metastases and/or carcinomatous meningitis. Participants with
previously treated brain metastases may participate provided they are radiologically
stable, ie, are without evidence of progression for at least 4 weeks by repeat
imaging, are clinically stable, and without requirement of steroid treatment for at
least 14 days prior to first dose of study treatment.

- Active known or suspected autoimmune disease (except that subjects are permitted to
enroll if they have vitiligo; type 1 diabetes mellitus or residual hypothyroidism due
to an autoimmune condition that is treatable with hormone replacement therapy only;
psoriasis, atopic dermatitis, or another autoimmune skin condition that is managed
without systemic therapy; or arthritis that is managed without systemic therapy beyond
oral acetaminophen and non-steroidal anti-inflammatory drugs).

- Has any condition requiring systemic treatment with corticosteroids, prednisone
equivalents, or other immunosuppressive medications within 14 days prior to first dose
of study drug (except that inhaled or topical corticosteroids or brief courses of
corticosteroids given for prophylaxis of contrast dye allergic response are
permitted).

- Receipt of an organ allograft.

- Treatment with antibiotics within 14 days prior to first dose of study drug.