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Mammary mucinous lesions: congeners, prevalence and important pathological associations

A retrospective histopathological study was undertaken to determine the prevalence of mucin filled ducts and their associated mucinous proliferation in 962 breast cancers and 335 benign lesions. A total of 38 (3%) cases with mucin filled ducts was identified and 27 (2%) of these showed mucin extravasation into the adjacent stroma, changes characteristic of mucocoele‐like lesions. This constitutes the largest series reported to date. Of the mucocoele‐like lesions 12 were prototypic screen‐detected cases; 11 of which were mammographically detected on account of suspicious microcalcification and eight cases (67%) exhibited mucinous atypical ductal hyperplasia without overt malignancy. A further 12 mucocoele‐like lesions were incidental findings in screen‐detected (11) and symptomatic (one) cancers, the majority of which were invasive ductal carcinomas of no special type. In six of these cases (50%), mucinous atypical ductal hyperplasia or ductal carcinoma in situ was present. Thirty mucinous carcinomas constituted 3% of all cancers and three cases had associated mucocoele‐like lesions. Mucinous atypical ductal hyperplasia or ductal carcinoma in situ was also associated with 11 cases of mucinous carcinoma. In six mucinous carcinomas, amorphous microcalcification with a similar appearance to that of benign mucocoele‐like lesions was identified in the mucin, suggesting a possible link between the two lesions. Mucin‐filled ducts or mucocoele‐like lesions were almost twice as frequent in screen‐detected as in symptomatic lesions. The presence of mucinous atypical ductal hyperplasia in screen‐detected mucocoele‐like lesions, a decade earlier than the peak of mucinous carcinoma, is a possible risk factor for subsequent invasive malignancy. Mucin‐filled ducts, mucocoele‐like lesions, mucinous atypical ductal hyperplasia or ductal carcinoma in situ and mucinous carcinoma may represent different stages of the same disease process. Our findings suggest that patients with mucin‐filled ducts of mucocoele‐like lesions merit close follow‐up.