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