Abstract: Background and purpose: Mucinous breast carcinoma is a kind of breast cancer that is prone to occur in elderly women with a good prognosis. Morphologically, it is characterized by a large amount of mucus in the extracellular stroma, in which cancer cells are floating. In infiltrating carcinoma of the breast with mucus secretion, tumor cells floating in mucus lake can be observed in a micropapillary shape. It is named as pure mucinous breast carcinoma with micropapillary pattern (MUMPC). This study aimed to explore the clinicopathological features of MUMPC and analyze the prognostic factors in patients with MUMPC. Methods: The clinicopathological data of 40 patients with MUMPC admitted to Changzhou Second People’s Hospital affiliated to Nanjing Medical University from Jan. 2010 to Dec. 2018 were retrospectively analyzed. The survival rate was calculated by Kaplan- Meier method. The log-rank test and COX regression model were used to analyze the effects of single and multiple prognostic factors. Results: All 40 patients were female, aged 30-80 years, and the median age was 56 years. All patients were followed up after surgery, with a follow-up time of 8.0-89.0 months and a median follow-up time of 60.0 months. The disease-free survival (DFS) rates at 1, 3 and 5 years were 100%, 87% and 62%, and overall survival (OS) rates at 1, 3 and 5 years were 100%, 95% and 85%. The results of single factor analysis showed that TNM stage, maximum tumor diameter, lymph node metastasis, vascular invasion, nuclear grade, neuroendocrine markers, molecular typing and Ki-67 proliferation index were the relevant factors affecting the prognosis of MUMPC patients (P<0.05). The results of multivariate analysis showed that TNM stage, nuclear grade and lymph node metastasis were the only risk factors affecting the prognosis of MUMPC patients (P<0.05). Conclusion: The incidence of MUMPC was relatively low, and the 5-year OS rate was relatively high. TNM stage, tumor nuclear grade and lymph node metastasis were independent risk factors affecting the prognosis of MUMPC patients.

Key words: Pure mucinous breast carcinoma, Micropapillary structure, Pure mucinous breast carcinoma with micropapillary pattern, Prognostic factors