Microinvasive carcinoma of the breast: diagnostic criteria and clinical relevance - Introduction

A microinvasive carcinoma is defined as a tumour in which the dominant lesi on is DCIS but in which there are one or more clearly separate foci of infi ltration of nonspecialized interlobular or interductal fibrous or adipose t issue, none measuring more than 1 mm (about 2 high-power fields) in maximum diameter. This definition is very restrictive and tumours fulfilling the c riteria are consequently very rare. If there is sufficient doubt about the presence of invasion, the case should be classified as DCIS. Microinvasion is largely restricted to high nuclear grade types of DCIS, mainly of comedo type. Cases of apparently pure comedo DCIS should thus be extensively sampled to exclude invasion. Microinvasive carcinomas should likewise be extensively s ampled in order to exclude the possibility of larger invasive foci. Where s uch foci are found, the lesion should be classified as an invasive tumour. Small invasive carcinomas without an in-situ component are classified as in vasive.