Abstract P3-08-01: Clonal hematopoiesis of indeterminate potential (CHIP) in metastatic triple negative breast cancer
Authors: Santos Katheryn , Jin Qingchun , Miller Peter G. , Patel Ashka , Kirkner Gregory J. , Files Janet L. , Hughes Melissa E. , Stokes Samantha M. , Tayob Nabihah , Stover Daniel G. , Gibson Christopher J. , Winer Eric P. , Lin Nancy U. , Garber Judy E. , Parsons Heather A. 
Published: March 2022

Abstract
Background. Patients (pts) with metastatic triple negative breast cancer (mTNBC) receive serial cytotoxic chemotherapy regimens, often with cumulative myelosuppressive effects, impairing treatment tolerance. Clonal hematopoiesis of indeterminate potential (CHIP) refers to the detection of somatic mutations in genes recurrently mutated in hematologic malignancies in the blood of adults with no evident hematologic abnormalities. Little is known about the natural history of CHIP after breast cancer treatment. We sought to characterize CHIP in pts undergoing treatment for mTNBC. Methods. In this retrospective cohort study we identified 149 pts with biopsy-proven mTNBC at a single tertiary care institution with at least one blood sample collected within six months of metastatic diagnosis. We performed targeted sequencing of cryopreserved peripheral blood mononuclear cell (PBMC)-derived genomic DNA and defined CHIP as the presence of at least one pathogenic somatic mutation present at variant allelic fraction (VAF) of 0.02-0.35. We assessed the relationship between CHIP status and overall survival (OS), demographics, clinicopathologic features, germline mutation status, and type and timing of therapy. Results. We identified 27 unique CHIP variants across 22/149 pts (15%) within six months of metastatic diagnosis. Frequency of mutated genes were as follows: DNMT3A (n=15), PPM1D (n=4), TP53 (n=3), TET2 (n=2), SRCAP (n=1), ZBTB33 (n=1), ZNF318 (n=1). Median follow-up in the cohort was 37.9 months (IQR: 23.9-Not reached). The median age at time of blood draw was 55 years (IQR: 8.5) for pts with CHIP vs. 51 years (IQR: 16.5) for pts without CHIP. Ten (45%) pts with CHIP and 47 (37%) pts without CHIP were current or former smokers. Two (9%) pts with CHIP and 10 (7.9%) pts without CHIP were known germline mutation carriers of BRCA1, BRCA2 or PALB2. Twenty-two (100%) pts with CHIP and 124 (98%) pts without CHIP had received systemic chemotherapy for mTNBC prior to blood draw. There were no significant differences in type of chemotherapy regimen received between patients with or without CHIP. Twenty (90.9%) pts with CHIP vs. 96 (75.6%) of pts without CHIP had received radiation therapy prior to blood draw. Pts with CHIP had similar OS to those without CHIP (median OS 7.75 [2.20-31.7] vs. 9.33 [8.02-11.73] months). No pts developed therapy-related myeloid neoplasms (t-MN) or died of complications of cardiac disease. Conclusions. Pts with mTNBC had a higher frequency of CHIP than previously reported in age-matched healthy populations, but similar CHIP prevalence to what has been seen in cohorts of pts with solid tumors. Our study assessed for the presence of CHIP at only a single time point early in the metastatic course, but serial blood sampling later in treatment might reveal additional cases of CHIP. Though this cohort of patients with life-limiting mTNBC was small, presence of CHIP in the first six months of metastatic diagnosis was not associated with worse survival.
Citation Format: Katheryn Santos, Qingchun Jin, Peter G. Miller, Ashka Patel, Gregory J. Kirkner, Janet L. Files, Melissa E. Hughes, Samantha M. Stokes, Nabihah Tayob, Daniel G. Stover, Christopher J. Gibson, Eric P. Winer, Nancy U. Lin, Judy E. Garber, Heather A. Parsons. Clonal hematopoiesis of indeterminate potential (CHIP) in metastatic triple negative breast cancer [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P3-08-01.