Background. Several studies have suggested that ductal carcinoma in situ (DCIS) of the comedo type (variably defined) is biologically more aggressive than other patterns of DCIS and more likely to progress rapidly to invasive carcinoma.
Methods. Eighty-five pure DCISs were compared histopathologically with 64 carcinomas containing both intraductal and infiltrating ductal components (mixed DCIS/IDC).
Results. Solid DCIS with and without necrosis was seen more frequently seen in the mixed DCIS/IDC series, especially in cases with less than 50% DCIS. Periductal stromal inflammation and multifocality also were seen more frequently in mixed DCIS/IDC than in pure DCIS. High nuclear grade and high mitotic activity were also more common in the DCIS component of the mixed cases and were well correlated with the intraductal and infiltrating components of the same tumors in most of the cases. The frequency of axillary lymph node metastases was correlated with the proportions of stromal invasion but not with the DCIS subtypes. When the criteria (solid growth pattern, high nuclear grade, and central necrosis) for the diagnosis of intraductal comedocarcinoma were analyzed separately, the first of these correlated most strongly with mixed DCIS/IDC compared with pure DCIS, the second less strongly, and the third not at all, although central necrosis has been considered the main or only diagnostic criterion for comedocarcinoma in several previous reports.
Conclusions. Solid growth pattern and high nuclear grade are the most important histopathologic features of DCIS used to predict progression to invasive carcinoma. No major changes between the intraductal and invasive elements of the same tumors were noted, but other studies have suggested that markers of aggressiveness either increase or decrease in the progression to invasion. These conflicting data require further investigation.