Impact of Squamous Differentiation in Breast Carcinoma

This study attempted to review the impact of extent of squamous differentiation in 56 infiltrating duct carcinomas (IDC) with squamous differentiation (metaplastic squamous carcinomas [MSC]). Tumors showing 100% squamous elements were labeled as primary squamous carcinomas (PSC; n = 28) and compared with 28 MSC showing lesser squamous components. A clinicopathological comparison revealed that lymphovascular emboli were never seen in any PSC but were noted in 7/28 of other MSC, while perineural invasion was seen only in PSC and not in MSC. Nodal metastasis was significantly more in other MSC as opposed to PSC. Most MSC presented with 2- to 5-cm sized tumors while PSC were 5 to 10 cm in size. PSC showed cystic change while MSC did not. Disease free survival (DFS) for MSC versus PSC was 64% versus 39.8%, while overall survival (OAS) was 72.7% in MSC versus 66.7% in PSC. Tumor stage affected DFS in MSC while none of the factors affected DFS/OAS in PSC. The extent of squamous differentiation affected DFS with best behavior for metaplastic carcinomas showing <40% squamous elements and worse for those with >90% squamous component (P = .024). PSC of breast is an aggressive disease and show distinct clinicopathological features from other MSC, and though the current definition of MSC does not advocate quantifying the squamous element, clearly this affects prognosis.