Breast ductal carcinoma in situ with microinvasion: a definition supported by a long-term study of 1248 serially sectioned ductal carcinomas.

BACKGROUND: The significance of microinvasion is still debated and clinical management is controversial. The authors defined ductal carcinoma in situ with microinvasion (DCIS-MI) as DCIS with infiltration of the periductal stroma by a few tumor cells, singly (type 1) or in clusters (type 2). With this definition, the authors attempted to evaluate the clinical significance of microinvasion.
METHODS: The authors compared the clinical, pathologic features, and survival (median follow-up, 7.3 years) of 1248 patients with, respectively, DCIS (722 patients), DCIS-MI with microinvasion type 1 and type 2 (243 patients), and invasive ductal carcinoma in situ with a predominant DCIS component greater than or equal to 80% of the tumor (IDC-DCIS, 283 patients).
RESULTS: Microinvasion was associated with DCIS histologic type, grade, and extent (respectively, P < 10(-8), P < 10(-3), P < 10(-4)). Axillary lymph node metastases were observed in a few patients with DCIS and DCIS-MI type 1 (respectively, 1.4% and none), in 10.1% with DCIS-MI type 2 and in 27.6% with IDC-DCIS. Metastasis free and overall survival probabilities were significantly different between three groups in the following order from best to worst prognosis: 1) the group comprising DCIS and DCIS-MI type 1, 2) the DCIS-MI type 2 group, and 3) the IDC-DCIS group.
CONCLUSIONS: The authors' results suggest there are two types of DCIS-MI: 1) type 1 that behaves like DCIS and should be managed as such; 2) type 2 that is less pejorative than IDC-DCIS but is more so than type 1. Copyright 2002 American Cancer Society.