Mucinous Carcinoma of Breast: A Histopathological and Immunohistochemical Study

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Introduction: Mucinous Carcinoma (MC) is a special type of breast cancer. It comprises 4% (1-7%) of all invasive breast cancer. MC is also called colloid breast cancer characterised by nests of cells floating in lakes of mucin. It is divided into two subtypes Pure Mucinous Carcinoma (PMC) and Mixed Mucinous Carcinoma (MMC). PMC classified into two main types according to its structural and cytological features type A (paucicellular) the classical variant with a large amount of extracellular mucin, and type B (hypercellular) a hypercellular variant with less mucin and often with neuroendocrine differentiation. Hormone receptors, Human Epidermal growth factor Receptor-2 (HER2) and MUC2 status play an important role in prognosis and management. Aim: To study histopathological features of MC breast and Immunohistochemical (IHC) status. Materials and Methods: A retrospective study of patients who presented with breast cancer were studied at Department of Pathology, Karnataka Institute of Medical Sciences, Hubballi, Karnataka, India. The study was analysed in June 2002 and authors included data from January 2021 to June 2022. The data included the age at diagnosis, Tumour (T), Lymph Nodes (N), and Metastases (M) (TNM) stage, presence and number of Lymph Node (LN) metastases, Oestrogen Receptor (ER), Progesterone Receptor (PR), HER2 and MUC2 status. The patients in whom the diagnosis of MC of breast was given on histopathology were only included in the study. Patients of breast cancer of other pathological types were excluded from the detailed study. Descriptive statistics like mean, tables, and charts were used with the help of Microsoft office 2007 to interpret the results. Results: A total of 245 patients reported as invasive breast cancer during 18 months of study period, out of which 12 cases diagnosed as MC were taken in study. Amongst 12 cases, eight cases were PMC and four cases were MMC. The mean age at presentation was 63.37±16.38 years (eight PMC) and 60.0±19.30 years (four MMC). A total of 11 out of 12 cases were females and only one was male case (PMC). Majority of PMC 04 (50.0%) and MMC 03 (75.0%) were observed to be in TNM Stage 2, and four of 12 cases of MC had LN metastasis with no distant metastasis. MC showed higher expression of hormone receptors and lower expression of HER2/neu and MUC2 positivity, which corroborates with other studies and concluded that, MC with such an immunohistochemistry profile was prognostically better. Conclusion: Mucinous Breast Carcinoma (MBC) is a rare type of breast cancer accounting for about 4% of all diagnosed breast cancers. These are associated with a better long-term prognosis than other breast cancers. Hormone receptors and HER2 status play an important role in prognosis and management. MUC2 also plays a major role in mediating the proliferation, apoptosis, metastases of breast cancer cells and determining the use of chemotherapy drugs.