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 is an open-label, multicenter, two-arm Phase II clinical trial that will evaluate the impact of 2nd line chemotherapy (i.e. capecitabine) on survival in patients with non-Luminal A hormone receptor-positive (HR+) metastatic breast cancer (MBC)

This study is researching an investigational drug called REGN7075 by itself and in combination with cemiplimab with or without chemotherapy. The study is focused on patients with certain solid tumors that are in an advanced stage. The aim of the study is to see how safe and tolerable REGN7075 is by itself and in combination with cemiplimab (with or without chemotherapy), and to find out what is the best dose of REGN7075 to be given to patients with advanced solid tumors when combined with cemiplimab (with or without chemotherapy). Another aim of the study is to see how effective REGN7075 by itself, or in combination with cemiplimab (with or without chemotherapy), is at treating cancer patients.

The study is also looking at:

* Side effects that may be experienced by people taking REGN7075 by itself and in combination with cemiplimab with or without chemotherapy
* How REGN7075 works in the body by itself and in combination with cemiplimab with or without chemotherapy
* How much REGN7075 is present in the blood when given by itself and in combination with cemiplimab with or without chemotherapy
* To see if REGN7075 by itself and in combination with cemiplimab with or without chemotherapy works to treat cancer by controlling the proliferation of tumor cells to shrink the tumor

This is a Phase 1b open-label, 2-part study in 3 treatment groups. The 3 treatment groups are as follows:

Treatment Group 1: Palazestrant (OP-1250) in combination with ribociclib (KISQALI, Novartis Pharmaceuticals Corporation).

Treatment Group 2: Palazestrant (OP-1250) in combination with alpelisib (PIQRAY, Novartis Pharmaceuticals Corporation).

Treatment Group 3: Palazestrant (OP-1250) in combination with everolimus.

Treatment Group 4: Palazestrant (OP-1250) in combination with atirmociclib.

This Phase III Trial evaluates whether breast conservation surgery and endocrine therapy results in a non-inferior rate of invasive or non-invasive ipsilateral breast tumor recurrence (IBTR) compared to breast conservation with breast radiation and endocrine therapy.