Intraductal carcinoma associated with invasive carcinoma of the breast. A comparison of the two lesions with implications for intraductal carcinoma classification systems.

Intraductal carcinoma (DCIS) is a useful marker for predicting which women will develop a recurrent breast malignancy. The authors examined 150 consecutive, mammographically detected, T1 invasive carcinomas associated with DCIS to study the DCIS and compare it to its associated invasive carcinoma. Intraductal carcinoma nuclear grades were assigned to each duct on a scale of 1 to 3. The percentage of DCIS ducts that were involved by each grade was quantitated into quartiles for cases with more than one DCIS nuclear grade. The predominant architectural pattern corresponding to each DCIS nuclear grade was recorded. Ninety-two percent of the 150 invasive carcinomas were of ductal type, 4% were tubular, and the remainder were various other subtypes. Nine percent of the DCIS cases were nuclear grade 1. The remaining 91% of cases were almost evenly distributed between mixed DCIS nuclear grades 1 and 2 (19%), pure DCIS nuclear grade 2 (24%), mixed DCIS nuclear grade 2 to 3 (25%), and pure DCIS nuclear grade 3 (22%). Two percent of cases were a mixture of DCIS nuclear grades 1 and 3 or 1, 2, and 3. All pure DCIS nuclear grade 1 or mixed 1 and 2 were associated with well or moderately differentiated invasive carcinomas, whereas the majority (61%) of the pure DCIS nuclear grade 3 cases were associated with poorly differentiated invasive carcinomas. There was no relation between the DCIS architectural pattern and the invasive carcinoma grade. In general, the DCIS nuclear grade correlates with the grade of the invasive carcinoma. Unlike DCIS architecture, nuclear grade heterogeneity within DCIS associated with invasive carcinoma is minimal. DCIS classification systems based on nuclear grade have merit because there is little variation in nuclear grade within a given patient's lesion.