Immunohistochemical Tumor Characteristics of Breast Cancer according to Participation in the Mammography Screening Program

Abstract

Abstract Background Breast cancer detected in participants of the German Mammography Screening Program (MSP) shows a favorable distribution of prognostic parameters and hormone receptor status compared to cancer in non-participants, even including interval cancers. The aim of our study is to examine the distribution of intrinsic breast cancer subtypes considering the proliferation marker Ki-67 in participants and non-participants in a population-based setting and to evaluate the association between Ki-67 and tumour characteristics. Methods Population based data from the Epidemiological Cancer Registry Lower Saxony is analysed in this retrospectiv observational study. 1115 cases of breast cancer (in situ and invasive, year of diagnosis 2014) among women aged 50–69 years and residing in the regions of two screening units of Lower Saxony are included (n = 285 634 biennially entitled women). The group of the participants containes cancers that are detected by screening or in the interval of 24 month after a negative screening. The group of non-participants includes all breast cancers without match with screening data. Results Considering cases with invasive breast cancer (n = 953) tumours detected in screening participants are more often diagnosed in early T stage (T1, p < 0,0001), HER2 negativ (p = 0,0336), with lower Ki-67 percentage scores (p < 0,0003) and without loco-regional lymph node involvement (p < 0,0001), compared to tumours in non-participants – even including interval cancers. Regarding grading both groups show less differences (p = 0,1718), because interval cancer are more comparable with cancers in non-participants. We find distinct differences in distribution of the intrinsic suptypes between both groups (p < 0,0003): especially in category Luminal A (38,4 % vs. 26,7 %), but also in the categories Luminal A or B (26,7 vs. 22,1 %), Luminal B (21,1 vs. 30,6 %), HER2 enriched (5,1 vs. 7,8 %) und triple-negative (8,8 vs. 12,8 %). Ki-67 is associated with all analysed prognostic factors, first of all with grading (p < 0,0001). Discussion According to the S3-Guidelines an adjuvant chemotherapy can be avoided in the majority of Luminal A type breast cancers. Assuming that both groups received a guideline-based therapy MSP participants (including interval cancers) could be treated with less aggressive systemic therapy compared with cancers in non-participants. Our results indicate for both groups that Ki-67 is a prognostic marker, which is not independent of other histopathological factors.