Risk of secondary leukemias in patients with germline PALB2 pathogenic variants after chemotherapy exposure.

10598 Background: Pathogenic variants in germline cancer-predisposing genes (e.g. BRCA1/2, PALB2) confer an increased risk for solid tumors but not de novomyeloid malignancies. Many of these genes are related to DNA repair pathways. It is not known whether exposure to genotoxic therapy increases the risk of secondary hematologic malignancies. Here, we report the incidence of hematologic malignancy after a solid tumor diagnosis among patients with a germline PALB2 pathogenic variant. Methods: Patients were identified at the Massachusetts General Hospital Center for Cancer Risk Assessment among individuals seeking counseling and/or testing for hereditary cancer risk genes. Analyses were conducted using R version 4.2.2 “tidyverse” and “gtsummary” packages. Results: Of the 176 charts reviewed, 102 (57%) had a history of malignancy, of which 68 (66%) received genotoxic chemotherapy. The median follow-up after chemotherapy was 59mo (IQR =17,109). The most common malignancy and chemotherapy were breast cancer (n=76, 75%) and doxorubicin, cyclophosphamide, and paclitaxel (n = 21, 31%). We compared patient outcomes by receipt of chemotherapy or not. There was no difference in race, age at cancer diagnosis, surgery rate, treatment with hormone therapy, or secondary malignancy between the two groups (p > 0.05). There was higher incidence of radiation treatment in those receiving genotoxic therapy compared to those who did not (65% vs 41%, p = 0.024), but no difference Gray or in follow up after radiation. Mortality in the genotoxic therapy group was 15% (n=10) vs. 9% (n=2) in the no genotoxic therapy group (p =0.33). Two subjects developed a hematologic malignancy (one case each of CLL and CML); both had prior chemotherapy and radiation exposure (Table). Conclusions: Cancer survivors with a germline PALB2 pathogenic variant and subsequent exposure to genotoxic therapy appear to have low risk of secondary hematologic malignancy. Although two subjects in the chemotherapy group developed leukemias, given the cases seen it is unlikely that these relate to the treatment exposure. Given the small sample size and retrospective nature of this study, more investigation is necessary to fully quantify the risk of therapy-related myeloid neoplasm in patients with germline PALB2 pathogenic variants. Table: see text