p63 is useful in the diagnosis of mammary metaplastic carcinomas

p63 has been recently reported to be expressed in sarcomatoid/metaplastic carcinoma of the breast, in addition to its role as a myoepithelial marker. A large series of 34 metaplastic carcinomas, including cases with pure epithelial component (squamous cell and adenosquamous carcinomas), biphasic tumours with carcinomatous and sarcomatoid components and monophasic tumours with only spindle cell component, were evaluated for p63 expression with respect to the different cellular components.

All of the metaplastic carcinomas were assessed for p63 and conventional epithelial and mesenchymal markers of AE1/3, CAM5.2 and vimentin by immunohistochemistry.

All of the different categories of metaplastic carcinomas showed similar clinico-pathological features (patient age, tumour size, nuclear grade, mitotic activity, lymph node status and hormonal receptor status). For metaplastic carcinoma with epithelial component only, p63 was only expressed in the squamous cell component, but not the adenocarcinoma component. Eight of the 10 tumours were positive for p63. For the tumours with sarcomatoid component, either singly or together with carcinomatous component, p63 was positive in 14 of 24 cases. Pure sarcomas and carcinomas were all negative for p63 staining by immunohistochemistry, thus rendering p63 staining highly specific for diagnosing metaplastic carcinoma.

Using p63 for diagnosis of metaplastic carcinoma gives a sensitivity of 65%, a specificity of 96%, a positive predictive value of 96%, and a negative predictive value of 66% and an accuracy of 78%. p63 may be used as an adjunct marker in the diagnosis of metaplastic carcinoma.