Mucinous Micropapillary Carcinoma of Breast in a Developing World Setting: Case Series With Clinicopathological Insights and Survival Analysis From a Tertiary Care Hospital.

Introduction and Importance: Mucinous micropapillary carcinoma breast (MMPC) is one of the rarest subtypes of breast cancer (BC) with clinicopathologic features correlated with poor prognosis. We are aimed at identifying MMPC cases and correlate them with histopathological features, overall survival (OS), and recurrence-free survival (RFS). Case Presentation/Materials and Methods: We retrospectively identified cases of MMPC from our institutional repository from 2017 to 2022. Data were collected regarding age, stage of BC at the time of diagnosis, tumor size, lymphovascular invasion (LVI), extranodal extension (ENE), lymph node (LN) metastasis, tumor biology, recurrence, and OS. Quantitative variables are calculated as median with range (IQR), whereas qualitative variables are presented in percentages. Clinical Discussion/Results: Nine MMPC cases were reported in the last 6 years, with a median age at diagnosis of 49 years. At diagnosis, 66.67% (6/9) were Stage III followed by Stage II; the average tumor size was 4.5 cm and the majority of tumors were Grade II (77.78%) followed by Grade III. LVI was seen in 66.67%, ENE in 33.33%, and LN metastases in 66.67%. Estrogen receptor (ER)/progesterone receptor (PR) was positive in 77.78%. The OS was 7/9 (77.78%) at the median follow-up of 3.5 years; recurrence was reported in two patients with an RFS of 77.78% (7/9). Conclusion: Our results demonstrate that MMPC is a rare entity that presented at a younger age with more advanced disease. Patients presented with larger tumor size, intermediate- to high-grade tumor morphology, LVI, ENE, and LN metastasis. These tumors also overexpressed ER and PR. Despite this, clinical outcomes in our cohort were relatively favorable, which is also reflected in OS (77.78%) and RFS (77.78%) at a median follow-up of 3.5 years.