RESUMEN
Objective: To investigate the expression of MSI1 and HER2 in mammary Paget's disease, and the correlation between the expression levels of MSI1 and HER2 and the clinicopathologic characteristics and prognosis of the patients. Methods: Clinical data and paraffin-embedded specimens of 34 pairs of mammary Paget's disease and underlying breast cancer were collected at the Department of Pathology, Affiliated Lianyungang Oriental Hospital of Xuzhou Medical University from March 2011 to December 2019. Immunohistochemistry was used to detect the expression of MSI1 and HER2 in mammary Paget's disease and the accompanying breast cancer, and to analyze the correlation between the expression levels of MSI1 and HER2 and their clinicopathologic features, as well as their influence on prognosis. Results: In mammary Paget's disease, the positive rate of MSI1 was 91.2% (31/34) and the positive rate of HER2 was 88.2% (30/34); the expression of MSI1 and HER2 was positively correlated (P=0.001, r=0.530). The expression of MSI1 was positively correlated with menopausal status (r=0.372, P=0.030) and lymph node metastasis (r=0.450, P=0.008). HER2 expression was positively correlated with menopausal status (r=0.436, P=0.010), and negatively correlated with ER expression (r=-0.365, P=0.034). The co-expression of MSI1 and HER2 was positively correlated with age (r=0.347, P=0.044) and menopausal status (r=0.496, P=0.003), and negatively correlated with ER expression (r=-0.461, P=0.006). Conclusions: MSI1 and HER2 are highly expressed in mammary Paget's disease and their expression levels are positively correlated. The correlation analysis between clinicopathological features and prognosis suggests that both of them may be involved in the occurrence and development of mammary Paget's disease and are potential therapeutic targets for mammary Paget's disease.