An Open-label, Phase I Dose Escalation and Phase 2 Dose Expansion Study to Assess Safety, Tolerability, Preliminary Antitumor Activity of SMP 3124LP in Adults with Advanced Solid Tumors

The purpose of this study is to test the safety and effectiveness of the sequence of two investigational drugs (trastuzumab deruxtecan followed by datopotamab deruxtecan, or datopotamab deruxtecan followed by trastuzumab deruxtecan) to learn whether the treatment works in treating HER2-negative (HER2-low or HER2-0) metastatic breast cancer.

The names of the study drugs involved in this study are:

* Datopotamab deruxtecan (a type of antibody drug conjugate)
* Trastuzumab deruxtecan (a type of antibody drug conjugate)

The purpose of this study is to determine if a combination of two drugs sacituzumab govitecan and atezolizumab works as a treatment for residual cancer in the breast or lymph nodes and have circulating tumor DNA in the blood.

This research study involves the following investigational drugs:

* Sacituzumab govitecan
* Atezolizumab