Genotype-Specific Effects of Clonal Hematopoiesis of Indeterminate Potential (CHIP) on Breast Cancer

Abstract

Clonal hematopoiesis of indeterminate potential (CHIP) is characterized by expanded blood cell clones containing somatic mutations in leukemia-associated genes in patients without hematologic malignancies. A growing body of research indicates that CHIP is associated with aberrant inflammatory signaling, and studies have identified high rates of CHIP in patients with solid tumors. CHIP has been associated with adverse outcomes in some solid tumor settings, but its impact on breast cancer remains unclear. This dissertation leverages orthogonal approaches with clinical data and mouse models to investigate the impact of CHIP on breast cancer progression and the breast tumor microenvironment. We identified a retrospective cohort of 125 patients presenting with primary breast cancer and used targeted sequencing on peripheral blood to identify CHIP. Metastatic outcomes were curated via chart review, and distant metastasis-free survival probability was analyzed. In parallel, we used bone marrow transplantation to develop novel chimeric mouse models of CHIP. Sublethally irradiated mice received mixtures of wildtype cells and CHIP-mutant hematopoietic cells representing the two most common CHIP genotypes observed in patients (Dnmt3a and Tet2). After engraftment, CHIP and control mice were injected with syngeneic breast cancer cells into the mammary fat pad. Tumor growth was measured regularly, and at tumor endpoint, peripheral blood and breast tumors were harvested for analysis of immune cell abundance via mass cytometry. Patients with high-burden CHIP (variant allele frequency > 10%) and non-DNMT3A CHIP had significantly shorter distant metastasis-free survival. In vivo, mice with Tet2-CHIP developed larger primary tumors and were more likely to experience lung metastasis, while Dnmt3a-CHIP did not differ from controls. The general immune subsets observed in both CHIP models were similar, but immunophenotyping revealed clonal expansion and immune cell subset skewing specific to the Tet2-CHIP model. This work demonstrates a genotype-specific impact of CHIP on breast cancer across human and mouse data. Further, the chimeric models described offer a clinically relevant tool to study solid tumors in a CHIP background. These results underscore the need for further functional studies and personalized risk assessment to clearly define the impact of various CHIP genotypes on solid tumors