Germline Mutations and the Presence of Clonal Hematopoiesis of Indeterminate Potential (CHIP) in 20,963 Patients With BRCA-Associated Cancers

**Background:**The contribution of germline genetics on the emergence of CHIP in patients with solid tumor malignancies is not well understood. We hypothesized that those with germline (g) alterations in homologous recombination repair genes (gHRR) and BRCA-associated cancers (breast, ovarian, prostate, pancreas) would have different rates of CHIP than those without.

**Methods:**We analyzed a large real-world Tempus multimodal database of paired germline and somatic DNA sequencing results. CHIP was calculated based on the presence of pathogenic or likely pathogenic alterations in any one of 16 CHIP-associated genes (ASXL1, BCOR, BCORL1, CBL, CREBBP, CUX1, DNMT3A, GNB1, JAK2, PPM1D, PRPF8, SETDB1, SF3B1, SRSF2, TET2, U2AF1) with a variant allele frequency of at least 2%. Patients with g alterations in BRCA1, BRCA2, ATM, CHEK2, and PALB2 were compared to those without gHRR alterations (sporadic).

**Results:**In breast cancer, patients with g_BRCA1_ (n = 104) mutations were younger (med 43 yrs) at diagnosis compared to sporadic cases (n = 6,546 med 56yrs) but had similar rates of CHIP (3% vs 5%). Those with gPALB2 (n = 42 med age 55) had the highest rate of CHIP (14%). gBRCA2 (n = 148; med age 52), gATM (n = 57 med age 52), and gCHEK2 (n = 57 med age 53) and similar rates of CHIP (3%, 4%, 7%). In ovarian cancer, patients with gBRCA1 (n = 137 med age 53) were younger at diagnosis than sporadic cases (n = 3,979 med age 63) with similar rates of CHIP (4% vs 3%). Those with gBRCA2 (n = 83 med age 61) were similar (4%) and gPALB2 (n = 11 med age 68) had the highest rate of 9%. CHIP was not detected among patients with g_ATM_ (n = 23 med age 61) or g_CHEK2_ mutations (n = 9, med age 59). In prostate cancer, 4% of patients with sporadic cases had CHIP (n = 4,183 med age 66) compared to 4% in gBRCA2 (n = 109 med age 63) and 5% in gATM (n = 44 med age 66). gCHEK2 had 17% prevalence of CHIP (n = 12 med age 66) followed by gPALB2 (n = 12 med age 69). There were no CHIP mutations found among those with g_BRCA1_ (n = 16 med age 64). In pancreatic cancer, patients with g_BRCA2_ (n = 89 med age 64) and PALB2 (n = 20 med age 62) were younger at diagnosis, compared to sporadic cases (n = 5,176 med age 67) with lower rates of CHIP (1% gBRCA2, 0 PALB2, 5% sporadic). The highest proportion was in gBRCA1 patients (n = 20 med age 63) with 10%, gCHEK2 (n = 16 med age 68) with 6% and gATM (n = 60 med age 66) with 5%.

**Conclusions:**Despite younger age at diagnosis, patients with g_BRCA1_ had similar or higher rates of CHIP within breast and ovarian cancer. Women with g_PALB2_ alterations and breast and ovarian cancer, as well as men with g_CHEK2_ mutations and prostate cancer, had higher rates of CHIP. These data suggest that gHRR mutations may influence the prevalence of CHIP among patients with BRCA-associated cancers and more research is needed.

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