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?

This phase II trial investigates the effect of avelumab or hydroxychloroquine sulfate with or without palbociclib in treating patients with stage II-III breast cancer that is positive for disseminated tumor cells (DTCs) after curative therapy. DTCs are breast cancer cells that are asleep (dormant) in the bone marrow. There are multiple ways in which these cells stay alive, and three of these mechanisms are inhibited by the drugs in this trial. First, dormant cancer cells need a protein signal pathway involving CDK 4/6 to start dividing once they wake up in order to survive as an active cancer cell. Palbociclib works by blocking the CDK 4/6 protein and by doing so may limit the dormant cancer cell from being able to survive. In addition, palbociclib may also help both of the other drugs in the trial to work better. Second, dormant cancer cells also use a process called autophagy to generate their own nutrition, which can allow them to stay asleep. Hydroxychloroquine has been shown to block autophagy, which leads to starvation of the cells. Third, dormant cancer cells are able to hide from the bodys immune system. The immune system sends a type of cell called T cells throughout the body to detect and fight infections and diseasesincluding cancers. One way the immune system controls the activity of T cells is through the PD-1/PD-L1 (programmed cell death protein-1) pathway. However, some cancer cells hide from T-cell attack by taking control of the PD-1/PD-L1 interaction and this stops T cells from attacking cancer cells. Avelumab is an antibody designed to block the PD-1/PD-L1 pathway and helps the immune system in detecting and fighting dormant cancer cells. Because palbociclib, hydroxychloroquine, and avelumab work on the mechanisms that keep the dormant cells alive, taking one or a combination of these drugs may be able to eliminate DTCs.

This trial uses fluid measurements of the arm and MRI to determine biomarkers of lymphatic dysfunction in patients with breast cancer. Studying the lymphatic system (the part of your body that helps to process and clear waste products) in different ways will help doctors understand more about lymphedema (excess fluid after lymph nodes are removed) and help with prevention and management of lymphedema in patients with breast cancer.

This phase III trial compares the effect of continuation of treatment with pembrolizumab (usual approach) to observation only at preventing cancer from coming back in patients with early-stage triple-negative breast cancer (TNBC) who achieved a pathologic complete response after preoperative chemotherapy in combination with pembrolizumab. The usual approach for patients with early-stage TNBC who receive preoperative chemotherapy plus pembrolizumab is to continue to receive pembrolizumab for up to 27 weeks after surgery. Immunotherapy with monoclonal antibodies, such as pembrolizumab, may help the body's immune system attack the cancer, and may interfere with the ability of tumor cells to grow and spread. This trial may help researchers determine if observation is as good as receiving pembrolizumab for 27 weeks after surgery in triple-negative breast cancer patients who achieved a pathologic complete response after preoperative treatment with chemotherapy and pembrolizumab.