TY - JOUR T1 - Neuroendocrine tumours of the breast: a genomic comparison with mucinous breast cancers and neuroendocrine tumours of other anatomic sites JF - Journal of Clinical Pathology JO - J Clin Pathol SP - 10 LP - 17 DO - 10.1136/jclinpath-2020-207052 VL - 75 IS - 1 AU - Fresia Pareja AU - Mahsa Vahdatinia AU - Caterina Marchio AU - Simon S K Lee AU - Arnaud Da Cruz Paula AU - Fatemeh Derakhshan AU - Edaise M da Silva AU - Pier Selenica AU - Higinio Dopeso AU - Sarat Chandarlapaty AU - Hannah Y Wen AU - Anne Vincent-Salomon AU - Edi Brogi AU - Britta Weigelt AU - Jorge S Reis-Filho Y1 - 2022/01/01 UR - http://jcp.bmj.com/content/75/1/10.abstract N2 - Aims Breast neuroendocrine tumours (NETs) constitute a rare histologic subtype of oestrogen receptor (ER)-positive breast cancer, and their definition according to the WHO classification was revised in 2019. Breast NETs display histologic and transcriptomic similarities with mucinous breast carcinomas (MuBCs). Here, we sought to compare the repertoire of genetic alterations in breast NETs with MuBCs and NETs from other anatomic origins.Methods On histologic review applying the new WHO criteria, 18 breast tumours with neuroendocrine differentiation were reclassified as breast NETs (n=10) or other breast cancers with neuroendocrine differentiation (n=8). We reanalysed targeted sequencing or whole-exome sequencing data of breast NETs (n=10), MuBCs type A (n=12) and type B (n=11).Results Breast NETs and MuBCs were found to be genetically similar, harbouring a lower frequency of PIK3CA mutations, 1q gains and 16q losses than ER-positive/HER2-negative breast cancers. 3/10 breast NETs harboured the hallmark features of ER-positive disease (ie, PIK3CA mutations and concurrent 1q gains/16q losses). Breast NETs showed an enrichment of oncogenic/likely oncogenic mutations affecting transcription factors compared with common forms of ER-positive breast cancer and with pancreatic and pulmonary NETs.Conclusions Breast NETs are heterogeneous and are characterised by an enrichment of mutations in transcription factors and likely constitute a spectrum of entities histologically and genomically related to MuBCs. While most breast NETs are distinct from ER-positive/HER2-negative IDC-NSTs, a subset of breast NETs appears to be genetically similar to common forms of ER-positive breast cancer, suggesting that some breast cancers may acquire neuroendocrine differentiation later in tumour evolution.Data are available from the authors upon reasonable request. ER -