Abstract P3-12-10: Is the Biology of Breast Cancer (BC) Changing through Time? Results of a Two-Decade Single Belgium Institution Study

Abstract

Abstract Background: Some available data suggest a change in the biology of BC particularly an increase in the proportion of ER+ disease. These changes in biology could be a result of an increase diagnosis of screen-detected BC or to a true change in biology. Screening was introduced in Belgium in the 80's and systematic screening in 2001. Methods: From the invasive BC pts treated at IJB between 1987 and 2004, only pts with a postal code from the region of Brussels were selected, to avoid bias from heterogeneous geographic evolution during the accrual period. For each year, 30 pts with available tumor block and FU information were randomly selected and stratified by trimester. Pts files were reviewed and demographic, staging and outcome data were collected. A central pathology review was performed by two experienced pathologists in a ISO15189-accredited laboratory, with construction of TMAs for the analysis of histologic type and grade, ER, PgR, HER2, Ki67 (all by IHC). HER-2 2+ cases were confirmed by FISH. A pilot phase of 20 cases was done to verify consistency between the 2 pathologists. To investigate if there was statistical evidence for an increase or decrease of each marker over time, time was divided in 3 periods (87-92, 93-98, 99-04) and the Mantel-Haenszel chi-square test was used. Results: In total, 505 pts were included with a median FU of 6 years. Due to technical issues, we currently have grade assessed in 407 cases, ER in 346 cases, PR in 328 cases, HER2 in 328 cases and Ki-67 (on TMA) in 302 cases (275 pts with complete biological assessment). Missing markers are being reassessed and more complete data will be available for the meeting. We found no statistical evidence for a consistent evolution over time for age at diagnosis (P=0.12) or lymph node status (P=0.86). A decrease in the number of postmenopausal (PM) pts (P=0.02) and in tumor size (P=0.04), and an increase in lobular type (P=0.05) in the more recent years were seen. There was an increase of high proliferative (P<0.001) and PgR positive (P=0.03) tumors but no significant difference in ER (P=0.38) and HER2 (P=0.37) expression. There was an increase in grade 1 tumors (P<0.001) but 72% of all cases were grade 2. Between 1987 and 2000, 5-year overall survival seems to be increasing (P=0.01). Discussion: Screening for BC in Belgium is organized for ≥ 50 years-old; therefore, increased screening should increase age at diagnosis and proportion of PM pts, which we do not observe. These results could be interpreted as a concomitant increase of BC in younger pts. Some changes seen can be justified by increased use of screening (i.e. grade 1) but others can not (i.e. lobular and Ki67). Therefore, there seems to be a true change in the biology of BC over the last 2 decades. Funded by an unrestricted educational grant from Astra-Zeneca. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P3-12-10.