BackgroundPure mucinous breast carcinoma (PMBC) is uncommon and associated with better prognosis than mixed mucinous breast carcinoma (MMBC). A micropapillary pattern in PMBC has been identified although its prognostic significance is questionable.MethodsA retrospective review of 100 cases of mucinous carcinoma diagnosed between 2000 and 2009 was conducted. Two broad categories were studied: PMBC (more than 90% mucinous component; n=45) and MMBC (less than 90% mucinous component; n=55). PMBC was further subclassified as hypocellular/type A (n=37) and cellular/type B (n=8). Receptor status, clinicomorphological and prognostic features were compared without patient follow-up.ResultsMean age at diagnosis in PMBC and MMBC was 60 and 63 years, while mean tumour size was 1.65 and 2.5 cm, respectively. Mean age in type A and type B PMBC patients was 75 and 55 years, respectively. The majority of PMBCs were well differentiated, with two poorly differentiated cases as well. The majority of MMBCs were moderately differentiated. A micropapillary pattern was seen in 20% of PMBCs. Sentinel lymph nodes were positive in 18.5% of PMBCs and 16% of MMBCs. Non-sentinel lymph nodes were positive in 14% of PMBCs and 39% of MMBCs. A micropapillary pattern was seen in 60% of LN positive PMBCs and 14% of LN negative PMBCs. Furthermore, 95% of PMBCs were ER(+), 84% were PR(+) and 9% were Her-2(+); 91% of MMBCs were ER(+), 87% were PR(+) and 33% were Her-2(+).ConclusionsPMBCs with a micropapillary pattern were more frequently associated with nodal disease. PMBCs with axillary disease had one or more of the following: micropapillary pattern, high nuclear grade, Her-2 positivity, smaller tumour size or younger age. Hence, axillary staging by sentinel lymph node biopsy is recommended in PMBCs.