Pathological and biological differences between screen-detected and interval ductal carcinoma in situ of the breast

Background: The incidence of ductal carcinoma in situ (DCIS) has risen dramatically with the introduction of screening mammography. The aim was to evaluate differences in pathological and biological characteristics between patients with screen-detected and interval DCIS. Methods: From January 1992 to December 2001, 128 consecutive patients had been treated for pure DCIS at our institute. From these, 102 had been attending the Dutch breast cancer screening program. Sufficient paraffin-embedded tissue was available in 74 out of the 102 cases to evaluate biological marker expression (Her2/neu, ER, PR, p53 and cyclin D1) on tissue microarrays (TMA group). Differences in clinicopathological characteristics and marker expression between screen-detected and interval patients were evaluated. Screen-detected DCIS was classified as DCIS detected by screening mammography, when the two-year earlier examination failed to reveal an abnormality. Interval patients were classified as patients with DCIS detected within the two-year interval between two subsequent screening rounds. Results: Screen-detected DCIS was related with linear branching and coarse granular microcalcifications on mammography (p < .001) and with high-grade DCIS according to the Van Nuys classification (p = .025). In univariate analysis, screen-detected DCIS was related with Her2/neu overexpression (odds ratio [OR] = 6.5; 95%CI 1.3-31.0; p = .020), and interval DCIS was associated with low-grade (Van Nuys, OR = 7.3; 95% CI 1.6-33.3; p = .010) and PR positivity (OR = 0.3; 95%CI 0.1-1.0; p = .042). The multivariate analysis displayed an independent relation of Her2/neu overexpression with screen-detected DCIS (OR = 12.8; 95%CI 1.6-104.0; p = .018). Conclusions: These findings suggest that screen-detected DCIS is biologically more aggressive than interval DCIS and should not be regarded as overdiagnosis.