This phase IV trial evaluates how well giving standard of care (SOC) peptide receptor radionuclide therapy (PRRT) after SOC surgical removal of as much tumor as possible (debulking surgery) works in treating patients with grade 1 or 2, somatostatin receptor (SSTR) positive, gastroenteropancreatic neuroendocrine tumors (GEP-NETs) that have spread from where they first started (primary site) to the liver (hepatic metastasis). Lutetium Lu 177 dotatate is a radioactive drug that uses targeted radiation to kill tumor cells. Lutetium Lu 177 dotatate includes a radioactive form (an isotope) of the element called lutetium. This radioactive isotope (Lu-177) is attached to a molecule called dotatate. On the surface of GEP-NET tumor cells, a receptor called a somatostatin receptor binds to dotatate. When this binding occurs, the lutetium Lu 177 dotatate drug then enters somatostatin receptor-positive tumor cells, and radiation emitted by Lu-177 helps kill the cells. Giving lutetium Lu 177 dotatate after surgical debulking may better treat patients with grade 1/2 GEP-NETs.

This ComboMATCH patient screening trial is the gateway to a coordinated set of clinical trials to study cancer treatment directed by genetic testing. Patients with solid tumors that have spread to nearby tissue or lymph nodes (locally advanced) or have spread to other places in the body (advanced) and have progressed on at least one line of standard systemic therapy or have no standard treatment that has been shown to prolong overall survival may be candidates for these trials. Genetic tests look at the unique genetic material (genes) of patients' tumor cells. Patients with some genetic changes or abnormalities (mutations) may benefit from treatment that targets that particular genetic mutation. ComboMATCH is designed to match patients to a treatment that may work to control their tumor and may help doctors plan better treatment for patients with locally advanced or advanced solid tumors.

The goal of this clinical trial is to evaluate the safety of TOS-358 in adults with select
solid tumors who meet study enrollment criteria. The main questions it aims to answer are:

1. what is the maximum tolerated dose and recommended dose for phase 2?

2. how safe and tolerable is TOS-358 at different dose levels when taken orally once or
twice per day?