Evaluating Clonal Hematopoiesis in Tumor-Infiltrating Leukocytes in Breast Cancer and Secondary Hematologic Malignancies

Abstract

Chemotherapy and radiation therapy are the foundations of adjuvant therapy for early-stage breast cancer. As a complication of cytotoxic regimens, breast cancer patients are at risk for therapy-related myeloid neoplasms (t-MNs). These t-MNs are commonly refractory to antileukemic therapies and result in poor patient outcomes. We previously demonstrated that somatic mutations in leukemia-related genes are present in the tumor-infiltrating leukocytes (TILeuks) of a subset of early breast cancers. Here, we performed genomic analysis of microdissected breast cancer tumor cells and TILeuks from seven breast cancer patients who subsequently developed leukemia. In four patients, mutations present in the leukemia were detected in breast cancer TILeuks. This finding suggests that TILeuks in the primary breast cancer may harbor the ancestor of the future leukemogenic clone. Additional research is warranted to ascertain whether infiltrating mutant TILeuks could constitute a biomarker for the development of t-MN and to determine the functional consequences of mutant TILeuks.

Figure 1.

Sample selection and data analysis. Schematic illustration of patient selection, sequencing methods, and variant interrogation. TILeuk = tumor-infiltrating leukocyte.

Figure 2.

Mutations in secondary hematologic malignancies are present in tumor-infiltrating leukocytes (TILeuks). A) Mutation heat map showing variants found in the leukemia samples included in the targeted sequencing panel for the breast cancer (BC) samples. Percentages in the boxes reflect the variant allele fraction (VAF) observed in the respective TILeuk samples (ER = estrogen receptor; HER2 = human epidermal growth factor receptor 2; SNV = single nucleotide variant). B) Scatter plot showing the VAF in the acute myeloid leukemia (AML) sample vs in the TILeuk sample. Data points are annotated with gene name and colored to match patients in panel B. C) Line graph showing the VAF of the TILeuk and AML samples for select mutations in the four patients (MSK2, MSK4, MSK6, MSK7) who had enrichment of AML driver mutations in the TILeuk samples. Error bars indicate 95% confidence intervals. Complete list in Supplementary Table 2 (available online).