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 a specific gene mutation.

Clinical outcomes for this subtype of breast cancer, invasive micropapillary carcinoma (IMPC), have generally found it to be more aggressive with regard to histopathologic features, stage at presentation, and clinical outcomes compared with invasive carcinoma of no specific type.

Pathologists working with the Iowa Institute of Human Genetics (Iowa City, IA, USA) obtained formalin-fixed, paraffin-embedded tumor blocks from seven patients identified from the archives at their institution and tumor registry from 1997 to 2012. Each case was reviewed by two surgical pathologists and the previously documented diagnosis of IMPC was confirmed. Areas with the highest percentage of tumor were identified on the hematoxylin-eosin slide and corresponding areas from the unstained slides were manually microdissected using a razor blade.

Massively parallel (Next-generation) sequencing was performed using the Ion AmpliSeq Cancer Hotspot Panel version 2 (Life Technologies, Carlsbad, CA, USA). Mutation analysis for B-Raf proto-oncogene, serine/threonine kinase (BRAF) V600E was performed using a single nucleotide primer extension assay using the SNaPshot Multiplex kit (Applied Biosystems; Foster City, CA, USA). Immunohistochemistry studies for estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor 2 (Her2/Neu), phosphatase and tensin homolog (PTEN), and non-metastatic protein 23 homologue 1 (NM23H1) were performed using the same tumor blocks.

The scientists found no pathogenic mutations 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.

The authors concluded that no somatic mutation could be 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. The study was published on October 3, 2014, in the journal Pathology and Laboratory Medicine International.

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