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Does removal of DCIS decrease the incidence of invasive breast cancer?

2 Background: SEER data have shown that as the incidence of high grade DCIS increases, high grade invasive cancer decreases; but this is not true for low-grade DCIS. The purpose of this study was first to determine what proportion of DCIS is calcified, and second to explore the relationship between grade, invasiveness, and calcification, in an effort to model the effect of removing mammographically detected DCIS.


METHODS
A single-institution, retrospective review was performed to identify all patients diagnosed with DCIS or invasive cancer from 2003-2011 who had corresponding mammograms.


RESULTS
There were 337 cases of pure DCIS, 309 cases of pure invasive tumor, and 847 cases of invasive tumor with a DCIS component. Grade 3 invasive cancers were much more likely to be associated with DCIS compared to grade 2 or 1 cancers. (83% vs. 70% vs. 54%, p<0.001). Of the 1,184 cases with DCIS or a DCIS component, 601 (51%) were associated with mammographic calcifications. The presence of calcifications was strongly associated with DCIS extent, comedo and micropapillary histology, presence of necrosis, and grade of DCIS (p<0.001 for each). High grade DCIS was almost twice as likely to be calcified compared to low grade. Extrapolation to SEER data suggests that there is a large reservoir of undetected, non-calcified DCIS and this is largely of low grade.


CONCLUSIONS
These findings may explain why breast screening has reduced the incidence of high-grade invasive cancers, through diagnosing and excising high-grade DCIS, and yet has failed to reduce the incidence of low-grade cancers. [Table: see text].