A Study of XmAb®18087 in Subjects With NET and GIST

Inclusion Criteria:

- Histologically or cytologically confirmed well differentiated low or intermediate
grade (World Health Organization [WHO] Grade 1 or 2) NET of pancreatic,
gastrointestinal, lung, or undetermined origin that is locally advanced or metastatic
and has progressed within the past 12 months

- Histologically confirmed GIST that is locally advanced or metastatic

- NET and GIST tumors must be unresectable

- NET subjects must have progressed on or been ineligible for treatment with
somatostatin analogues (SSA) and at least one other FDA-approved targeted therapy
(everolimus or sunitinib).

- GIST subjects must have previously received all FDA-approved therapies (imatinib
mesylate, sunitinib malate, and regorafenib) for which they are eligible

- Must have disease measurable by RECIST 1.1 criteria using either computed tomography
(CT) or magnetic resonance imaging (MRI) scan

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

Exclusion Criteria:

- Diagnosis of high-grade (WHO Grade 3) or poorly differentiated NET; high-grade
neuroendocrine carcinoma; large cell neuroendocrine carcinoma, small cell carcinoma,
or mixed small and large cell carcinoma.

- Subjects currently receiving anti-cancer therapies (other than SSAs, which may
continue).

- Subjects who have received anti-cancer therapies within 2 weeks of the start of study
drug (including chemotherapy, radiation therapy, immunotherapy, etc.).

- Must not be experiencing a Grade 3 or 4 toxicity from previous anti-cancer treatment

- Must not be receiving other anti-cancer therapies (except somatostatin analogues,
which may be allowed)

- Must not have poorly controlled diabetes mellitus, known central nervous system
involvement by malignant disease or insufficient bone marrow, renal, or hepatic
function