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 of detecting DCIS at mammographic screening by assessing its biological characteristics and by comparing screen detected DCIS with a series of symptomatic DCIS lesions. METHODS: 222 Screen detected and 151 symptomatic cases of pure DCIS were identified. Their histological grade and the prevalence of necrosis were ascertained and compared. RESULTS: Of the screen detected lesions 28 (13%) were low grade, 40 (18%) intermediate grade, and 153 (69%) high grade. Of screen detected lesions 186 (87%) were necrotic and 29 (13%) were not. Of the 151 symptomatic lesions 24 (16%) were low grade, 34 (23%) intermediate grade, and 89 (61%) high grade. Of symptomatic lesions 112 (75%) were necrotic and 36 (24%) were not necrotic. Screen detected DCIS was more often necrotic (p=0.008) than symptomatic DCIS. CONCLUSIONS: As most DCIS detected at screening is high grade and necrotic, aggressive investigation of suspicious microcalcification at mammographic screening is advocated. Given the biological features of screen detected DCIS, the existence of an upper limit for the detection of DCIS by the NHS breast screening programme seems to be inappropriate.