The mucinous variant of columnar cell lesions

Aims: Mucin-producing columnar cell lesions (CCL) are a rare, new entity in the breast. The aim of this study was to describe the incidence and follow-up of mucinous CCLs. Methods and results: Of 4164 breast core needle biopsies (CNBs), 291 showed a CCL and 21 atypical ductal hyperplasia (ADH) originating in a CCL (ADH-CCL). Mucin production was present in 17 of 291 (5.8%) CCLs and three of 21 (14.3%) ADH-CCLs, together concerning 0.5% of all CNBs. The most common mucinous CCL pattern was a columnar cell change without atypia, and almost all were detected with microcalcifications as an abnormality at mammography. During a median follow-up of 3.1years, no invasive carcinoma or ductal carcinoma insitu was detected. MUC2 was expressed in intraluminal mucin in 12 of 15 (80%) mucinous CCLs, and showed cytoplasmic expression in five of 15 (33%) mucinous CCLs seen in CNBs. Moreover, mucinous CCLs were significantly more common in association with 46 mucinous carcinomas than in 46 ductal carcinomas (28% versus 9%). Conclusions: Mucinous CCLs are rare lesions, with an incidence of about 0.5% in breast CNBs, usually presenting with microcalcifications. Although these lesions might play a role in the mucinous progression spectrum, the short-term risk of progression to more advanced lesions seems to be low.