Clinicopathologic characteristics of HER2-positive metaplastic squamous cell carcinoma of the breast

Aims The aim of this study was to analyse the clinicopathological features and prognosis of human epidermal growth factor receptor-2 (HER2)-positive metaplastic squamous cell carcinoma (MSCC). Methods Fifty-eight patients with MSCC of the breast who were classified into 45 triple-negative and 13 HER2-positive subgroups diagnosed at the West China Hospital, Sichuan University, from 2004 to 2018, were enrolled. Clinicopathological features were collected and compared between HER2-positive MSCC, triple-negative MSCC, HER2-positive invasive breast carcinoma of no special type (NST) and triple--negative NST groups. In the prognostic survival analysis, HER2--positive MSCCs was compared with triple-negative MSCCs, HER-positive NSTs and triple-negative NSTs. Results Compared with triple-negative MSCCs, more patients with Ki-67 low expression were in HER2-positive MSCCs (p<0.05). More patients with HER2-positive MSCC than patients with HER2-positive NST were postmenopausal (p<0.05). Compared among HER2-positive MSCCs, triple--negative MSCCs and triple-negative NSTs, patients of HER2-positive MSCCs with high Ki-67 expression were the least, and HER2-positive MSCCs had more strongly associated with postmenopausal disease status (p<0.05). In survival analyses, HER2-positive MSCCs had a high risk of recurrence and poor prognosis (p<0.05). Lymph node status was significantly associated with the disease--free survival of patients with HER2-positive MSCC. Conclusion In conclusion, our study indicates that HER2-positive MSCC is an aggressive disease with unique clinicopathological characteristics. Both HER2-positive status and an SCC component are critical factors for poor prognosis. HER2--positive MSCC and triple-negative MSCC are distinct subgroups. Corresponding targeted therapy recommendations should be made for this HER2--positive MSCC group.