Should breast screening programmes limit their detection of ductal carcinoma in situ?

Previous research has shown that the detection of ductal carcinoma in situ (DCIS) aids the detection of small invasive cancers at mammographic screening. A correlation may therefore exist between a screening unit's DCIS detection rate and their small invasive cancer detection rate. We have therefore investigated the effect of DCIS detection rate on the detection of small (<15 mm) invasive cancers in the 95 units of the U.K. NHS Breast Screening Programme (NHSBSP).

DCIS detection rates were examined against large (> or =15 mm) and small (<15 mm) invasive cancer detection rates in women aged 50-64 years at prevalent and incident screens over a 3-year period.

After adjusting for background incidence, screening units with the highest DCIS detection of > or =1.3/1000 detected over 20% more small invasive cancers than units with DCIS detection rates within the NHSBSP guidelines of 0.5-1/1000 (P<0.001). Sixty percent of units had DCIS detection rates above the guidelines. There was no correlation between DCIS detection and > or =15 mm invasive cancer detection. The results suggest that over the range of DCIS rates studied, that for every two extra DCIS cancers detected, an additional small invasive cancer (<15 mm) is detected that may otherwise not have been. The results therefore provide supporting evidence that the detection of DCIS aids the detection of small invasive cancers.

Units with DCIS detection above the NHSBSP guidelines have significantly better small invasive cancer detection rates. The existence of an upper limit for DCIS detection within the NHSBSP may be preventing the detection of small invasive cancers, because units are not recalling some small clusters of calcification in order to keep DCIS detection rates down. The upper limit may therefore be inappropriate.