Case report: Heterogeneity in the primary lesions of invasive micropapillary breast carcinoma

Breast cancer (BC) is a complex and heterogeneous disease including different biological subtypes. This results in molecular and phenotypic heterogeneity within the BC. Stratification of tumors contributed to achieving better outcome in terms of response to therapy and overall survival. Little is known about the features of clonal heterogeneity in different lesion in BC patient. We reported a case of a 52-year-old woman who was diagnosed with luminal B (HER2-) BC and accepted chemotherapy. She achieved partial response based on RECIST 1.1 criteria. However, progressive disease (PD) was then identified with multiple subtypes including luminal B and triple-negative breast cancer (TNBC). Next-generation sequencing (NGS) technologies showed that the different regions of diseased tissue were originated from same clonal genes. We also demonstrated the clonal heterogeneity and gene characterization between lesions of luminal B and TNBC. The patient archived complete remission (CR) with a clear beneficial outcome from immunotherapy treatment. In addition, tumour mutational burden (TMB) and DNA damage repair (DDR) pathway were considered as potential biomarkers for better prediction of tumor immunotherapy efficacy.