Molecular and immunohistochemical profiling of invasive micropapillary carcinoma of the breast

Abstract

Alexandra Thomas,1 Ryan W Askeland,2 Natalya V Guseva,2 Ramakrishna Sompallae,2,3 Deqin Ma2 1Department of Internal Medicine, 2Department of Pathology, 3Bioinformatics Division, Iowa Institute of Human Genetics, University of Iowa Hospitals and Clinics, Iowa City, IA, USABackground: In this study, molecular and immunohistochemical profiling of invasive micropapillary carcinoma of the breast was used to identify potentially useful markers for targeted therapies with a focus on BRAF V600E mutation.Methods: Formalin-fixed, paraffin-embedded tumor blocks from seven patients were identified from the archives at our institution and tumor registry from 1997 to 2012. Massively parallel (Next-generation) sequencing was performed using the Ion AmpliSeq™ Cancer Hotspot Panel version 2 (Life Technologies, Carlsbad, CA, USA). Mutation analysis for BRAF V600E was performed using a single nucleotide primer extension assay. Immunohistochemistry studies for estrogen receptor (ER), progesterone receptor (PR), Her2/Neu, phosphatase and tensin homolog (PTEN), and non-metastatic protein 23 homologue 1 (NM23H1) were performed using the same tumor blocks. Staining for ER, PR, and Her2/Neu was scored according to American Society of Clinical Oncology/College of American Pathologists guidelines, and a four-tier system, ie, strong homogenous, heterogeneous, positive with negative foci, reduced in more than 50%, and lost in all or majority was used for PTEN and NM23H1 staining.Results: No pathogenic mutations were identified in the tumors by next-generation sequencing. The lack of BRAF V600E mutation was confirmed by single nucleotide primer extension assay. All tumors were positive for ER and PR, and showed no overexpression of Her2/Neu. Loss of or reduced PTEN expression was observed in six of seven cases and was associated with lymph node metastasis. Reduced NM23H1 expression was observed in three of seven cases, all of which had concurrent PTEN loss.Conclusion: No somatic mutation was identified consistent with the reported lack of driver mutations in this tumor. The frequent loss of PTEN in invasive micropapillary carcinoma may have implications for targeted therapy towards the phosphatidylinositol-4,5-bisphosphate 3-kinase pathway in this subgroup of patients.Keywords: invasive micropapillary carcinoma, next-generation sequencing, immunohistochemistry