Microinvasive carcinoma of the breast

Last revised by Bahman Rasuli on 21 Dec 2020

Microinvasive carcinoma is a type of epithelial breast cancer in which microscopic foci of tumor cells infiltrate the breast stroma.

Microinvasive carcinoma is defined histologically as one or more clearly separate foci of tumor cells ≤1 mm in size infiltrating the mammary stroma 1. It nearly always occurs in association with carcinoma in situ, typically high grade ductal carcinoma in situ and uncommonly lobular carcinoma in situ 1.

Microinvasive carcinoma is staged as T1mi in the TNM system for breast tumors.

When microinvasive carcinoma arises in the setting of high grade ductal carcinoma in situ, mammography typically detects calcifications, less commonly a mass, and even less commonly an asymmetry or architectural distortion 1,2.

In case series, the most common sonographic finding is a solid hypoechoic mass 2.

The dominant MRI findings are non-mass enhancement that is heterogeneous or clustered ring in internal pattern, segmental in distribution, and showing strong initial enhancement with delayed washout kinetics 3.

Outcomes are similar to that of pure ductal carcinoma in situ 1,4. Therefore, microinvasive carcinoma is managed like high grade ductal carcinoma in situ, i.e. with some combination of surgery, radiation therapy, and/or endocrine therapy.

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