Screen detected ductal carcinoma in situ (DCIS): overdiagnosis or an obligate precursor of invasive disease?

Objectives-Ductal carcinoma in situ (DCIS) represents 20%-25% of malignancy detected at mammographic screening. This study aims to clarify the value o f detecting DCIS at mammographic screening by assessing its biological char acteristics and by comparing screen detected DCIS with a series of symptoma tic DCIS lesions. Methods-222 Screen detected and 151 symptomatic cases of pure DCIS were ide ntified. Their histological grade and the prevalence of necrosis were ascer tained and compared. Results-Of the screen detected lesions 28 (13%) were low grade, 40 (18%) in termediate grade, and 153 (69%) high grade. Of screen detected lesions 186 (87%) were necrotic and 29 (13%) were not. Of the 151 symptomatic lesions 2 4 (16%) were low grade, 34 (23%) intermediate grade, and 89 (61%) high grad e. Of symptomatic lesions 112 (75%) were necrotic and 36 (24%) were not nec rotic. Screen detected DCIS was more often necrotic (p=0.008) than symptoma tic DCIS. Conclusions-As most DCIS detected at screening is high grade and necrotic, aggressive investigation of suspicious microcalcification at mammographic s creening is advocated. Given the biological features of screen detected DCI S, the existence of an upper limit for the detection of DCIS by the NHS bre ast screening programme seems to be inappropriate.