Mammographic features of pure mucinous carcinoma of the breast with pathological correlation.

OBJECTIVE: To determine the mammographic features of pure mucinous carcinoma of the breast and correlate them with the pathologic features. PATIENTS AND METHODS: The authors analysed 23 tumours identified as pure mucinous carcinoma of the breast in 22 patients, aged 40 to 92 (mean 64.9) years at the time of mammography (which took place between November 1975 and July 1992). The review covered mammographic features, clinical findings, pathological features and nodal status. RESULTS: Twenty (87%) of the lesions were palpable, and 4 (17%) were mammographically occult. At mammography, eight cases (35%) presented as ill-defined masses without calcifications, five (22%) as well-defined masses without calcifications, four (17%) as ill-defined masses with calcifications, one (4%) as a focal asymmetric opacity and one (4%) as pleomorphic calcifications only. Eleven (65%) of the 17 mammographically identified masses were irregular in shape, 4 (24%) were oval, and 2 (12%) were lobular. In 11 (61%) of the 18 cases involving masses or an opacity, the lesions were denser than normal breast parenchyma; in the others the lesions were isodense. All of the hyperdense lesions were greater than 1.9 cm in greatest diameter, as determined mammographically, whereas only one of the isodense lesions was greater than 1.9 cm in greatest diameter. In 17 (77%) of the 22 cases in which the border of the lesions could be evaluated histologically, the lesions had well-defined, pushing borders; the others had ill-defined, irregularly outlined borders. Calcifications were seen histologically in seven cases (30%) and were correlated with mammographically suspicious pleomorphic calcifications in three. Fourteen (82%) of the 17 patients who underwent axillary node dissection were free of nodal disease. CONCLUSIONS: The most common mammographic appearance of pure mucinous carcinoma was an ill-defined mass and the second most common was a well-defined mass. No spiculated lesions were observed in this patient group. Microcalcifications were seen in some cases but were less common than in breast cancers in general. Lesions more than 1.9 cm in greatest diameter tended to be hyperdense. A substantial proportion of pure mucinous carcinomas may be mammographically occult.