Primary mucinous cystadenocarcinoma of breast with sternal metastasis: A diagnostic challange

The WHO categorizes the breast tumors in various distinct histological types based on cell morphology and architecture. A widely accepted fact that the aggressive nature of the breast cancer can be determined by its histological type, grade, nodal status, and metastasis holds the ground even in the era of immunohistochemistry (IHC) and molecular. An extremely rare variant of primary breast carcinoma belongs to the family of mucin producing carcinoma sharing the same histology as the mucinous cystadenocarcinoma of the ovary and pancreas. The tumour typically occurs in postmenopausal women with a median patient age of 61 years. Due to the rarity of these tumors, there is an extreme paucity of literature on this topic. We report a case of 35 year old female with left breast lump and presternal swelling. Breast lumpectomy and total sternectomy was done and final diagnosis was given as Primary mucinous cystadenocarcinoma with sternal metastasis and Estrogen receptor (ER) and Progesterone receptors (PR) positivity.