Invasive Mucinous Carcinoma of the Breast and Response Patterns after Neoadjuvant Chemotherapy(NAC)

Abstract

Aims

Neoadjuvant chemotherapy (NAC) is often used to treat localized invasive breast cancer. Invasive mucinous carcinoma (IMC) is considered to be an indolent form of invasive breast cancer and is rarely treated with NAC. We report the largest series of IMC treated with NAC, and report a characteristic, but not well recognized, pattern of pathologic response. Methods and Results: Our series included 7 patients with IMC treated with NAC. Three patients presented with locally advanced disease, three patients had tumors that were Her/2Neu positive, and four patients had tumors with admixed mucinous and micropapillary features. Clinical and imaging assessment of response showed persistent and in some cases progressive disease, despite evidence of significant pathologic response in these cases. Pathologic assessment after NAC demonstrated marked reduction in tumor cellularity but with persistent space occupying mucin pools, showing acellular mucin in one case, <1% tumor cellularity in 3 cases, and 5-10% cellularity in 3 cases in both the treated breast and axillary lymph nodes. Conclusions: Persistent mass forming low cellular or acellular mucin pools can result in discordant clinical, imaging, and pathologic findings in IMC treated with NAC.

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