Columnar cell lesion (CCL), atypical ductal hyperplasia (ADH) and ductal carcinoma in situ (DCIS) may be premalignant lesion of mammary invasive carcinoma. A few recent investigators reported that the precursor lesions exhibited mucin production and they might be potential precursor lesion for mucinous carcinoma (mCA). This study aims to investigate the incidence and histopathologic characteristics of mucinous precursor lesions, including mucinous DCIS (mDCIS) and mucinous CCL (mCCL).

We retrospectively analyzed invasive carcinomas with mucin. Cases were grouped into three subgroups: pure mCA, mixed mCA, and invasive carcinoma of no special type with mucin production (IC of NST-m). Precursor lesions were evaluated with PAS and alcian blue staining.

Total 27 cases of invasive carcinoma with mucin were analysed and classified as 18 pure mCA, 7 mixed mCA, and 2 IC of NST-m. mDCISs were found in 12 pure mCA, 4 mixed mCA and 2 IC of NST-m. mCCLs were found in 7 pure mCA and 2 mixed mCA. Majority of mucin was identified in both cytoplasm and ductal lumen, while some tumors exhibited only cytoplasmic mucin. We also observed three patterns of mDCIS classifiable by location of mucin and architecture of tumor cells.

Cytoplasmic mucin suggested that mucinous feature of precursor lesions in the vicinity of mCA might not be a passive morphologic finding but be involved in development of mCA.