Mucinous carcinoma of the breast: further characterization of its three subtypes.

Nineteen cases of mucinous carcinoma of the breast were studied. Twelve tumours were of the pure type, and seven were mixed. All had abundant neutral and acidic mucin, and stained strongly with CAM 5.2. Of the 12 pure mucinous tumours, six were devoid of argyrophilic granules and were S-100 negative, and only one was CEA positive. All six patients are alive with no evidence of recurrence (mean follow-up 42 months). The other six pure mucinous tumours were rich in argyrophilic granules. Five of these showed S-100 positivity and all were CEA positive. One patient developed local recurrence and one died of myocardial infarction with no evidence of tumour recurrence (mean follow-up 80 months). Of the seven mixed tumours, only one contained an occasional cell with argyrophilic granules and four had variable degrees of CEA positivity. Two patients died and one developed bony metastasis (mean follow-up 40 months). Our findings emphasise the microscopic and prognostic differences between the three subtypes of mucinous carcinoma of the breast, and support the concept of dividing pure mucinous tumours into two distinct subtypes. We suggest that the latter subtyping can be qualitatively made on the basis of the presence or absence of argyrophilic granules in the tumour cells.