Clinicopathological and prognostic exploratory study of primary metaplastic squamous cell carcinoma of the breast

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.

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.

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.

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.