Pure and mixed mucinous carcinoma of the breast: fine needle aspiration cytology findings and review of the literature.

Objective: Mucinous (colloid) breast carcinoma accounts for 1-6% of all breast cancer. It comprises pure mucinous tumours and mixed infiltrating ductal carcinomas with a mucinous component. As this latter mixed form has a worse prognosis than pure colloid carcinoma, making this diagnosis on fine needle aspiration cytology (FNAC) might influence the choice of treatment.

Methods:   We report a consecutive series of 22 cases consisting of 17 mixed and five pure mucinous carcinomas diagnosed by cytology and verified on histopathology. Patients underwent FNAC at the one-stop clinic of our institution during a 7-year period of time. Cytological findings were evaluated by a semi-quantitative method and included percentage of smear surface occupied by mucin, shape of cell groupings, size and outline of tumour nuclei as well as presence or absence of nucleolus.

Results:   Three of five pure mucinous carcinomas displayed at least two of the following features: abundant mucin, small nuclei and/or regular nuclear outlines. Sparse mucin, large nuclei, irregular nuclear outlines or the presence of nucleoli were found in 7 out of 17 mixed mucinous carcinomas but not in pure tumours.

Conclusion:   Cytopathological identification of patients with pure mucinous carcinomas may be performed in a limited number of cases.