Abstract
BACKGROUND: To investigate the clinicopathological characteristics of primary metaplastic squamous cell carcinoma of the breast (PMSCCB), and analyze the correlation among immuno-molecular phenotype, treatment and prognosis, in order to facilitate the subsequent precise treatment. METHODS: The clinicopathological data and paraffin-embedded tissue of 26 cases of PMSCCB were collected and analysed, and the relevant literatures were also studied. Given the limited sample size collected, the results are considered a preliminary exploratory analysis. RESULTS: Twenty-six female patients, with a mean age of 53.11 ± 10.83 years, had no previous history of squamous cell carcinoma. Grossly, the tumor exhibited a solid or cystic-solid appearance, with the maximum diameter averaging 3.73 ± 2.53 cm. Microscopically, there were 18 cases of pure squamous cell carcinoma and 8 cases of mixed type. The immuno-molecular phenotype of the sample was characterised by negative rates of ER, PR, and HER-2 at 65.4% (17/26), 92.3% (24/26) and 69.2% (18/26), positive rates of HER-2 FISH, HPV RNAscope, CK5/6, p63 and EGFR at 19.2% (5/26), 4.1% (1/24), 100% (26/26), 100% (26/26) and 96.0% (24/25), respectively. Most of the 26 patients underwent surgery and chemotherapy, with some receiving additional radiotherapy or targeted therapy. After a median follow-up of months (range, 9-134 months), 17 cases had no recurrence, 8 cases had distant metastasis and 1 case was lost to follow-up. CONCLUSIONS: PMSCCB occurs exclusively in females, with a mean age of onset of 53.11 ± 10.83 years, and 46.1% of the patients were premenopausal. It is characterized by high expression of CK5/6, p63, and EGFR, which can aid in diagnosis. There is low expression of ER, PR, and HER-2, which may offer opportunities for targeted and endocrine therapies. Anthracyclines combined with cyclophosphamide or/and taxanes may prove effective in chemotherapy treatment. p16-positive expression does not necessarily indicate high-risk HPV infection, and the expression of p53, p16 and EGFR is not correlated with prognosis. However, distant metastasis and GATA3 expression are significant factors influencing the prognosis of PMSCCB.