Immunoprofile of metaplastic carcinomas of the breast

Aims Metaplastic breast carcinoma ( MBC ) is a rare type of breast cancer; its diagnosis in routine practice can be challenging, and may require immunohistochemical ( IHC ) characterization if no conventional invasive or in‐situ carcinoma is present. Previous IHC studies of MBC often had a small sample size and did not investigate the different histological subtypes. This study aimed to assess the immunoprofile of MBC subtypes in a large series. Methods and results A total of 172 MBC diagnosed in routine and referral practice in Nottingham during 26 years were reviewed by three breast pathologists. In addition, data on the immunoprofile of 730 MBC in 61 published studies were analysed. The antibodies to a broad spectrum of cytokeratins ( AE 1/ AE 3 and MNF 116) are most frequently positive in MBC (approximately 80%). Basal cytokeratins (34βE12, CK 5/6, CK 14 and CK 17) are positive in approximately 70%. Luminal cytokeratins ( CK 8/18, CK 7 and CK 19) are positive in approximately 30–60%. Myoepithelial markers are also frequently positive, particularly p63. Oestrogen receptor ( ER ), progestogen receptor ( PR ) and HER 2 are usually all negative. CD 34 (a marker often positive in phyllodes tumours) is consistently negative in MBC . Conclusion This study provides data on the frequency of expression of a wide range of markers in MBC based on a large number of tumours. No consistent immunophenotype was identified and no individual marker was positive in all tumours, most probably reflecting the morphological and molecular heterogeneity of this tumour class and the practical need to use a panel of different antibodies when trying to establish the diagnosis of metaplastic breast carcinoma.