Reduction in rate of node metastases with breast screening: consistency of association with tumor size.

Population screening has brought about changes in both the incidence and mortality rates of patients with breast cancer. Large numbers of small screen-detected tumors have inspired discussions about overdiagnosis based on potential biological differences between screen-detected and symptomatic cancers. In the current systematic review, we analyzed the relation and the interaction of tumor size and nodal status in correlation with screening. Smaller tumors were more frequently screen detected (pT1 78.5 %) than symptomatic (pT1 61.7 %, p < 0.001), with a RR of 1.6 (95 % CI 1.4-1.8, n = 41,209). In the screened population, pT1 tumors were also more frequent (68.5 vs 49.9 %, n = 51,171, p < 0.001). Positive lymph nodes were less frequent in screen-detected tumors (26.8 vs 46.3 %, n = 43,705, p < 0.001) as well as in screened populations as a whole (24.1 vs 44.9 %, n = 49,581, p < 0.001). The relation between size and nodal status was not different between the screen-detected and the symptomatic tumors [pT2+N+ OR 2.42 (95 % CI 1.69-3.48) vs OR 2.91 (95 % CI 2.41-3.51)], suggesting that biological differences, if present, are small. In this systematic review, we confirmed both the association of screening with smaller tumor size at presentation and the consequent reduction in lymph node metastases.