Incidence and Demographic and Tumor Characteristics of HER2-Positive Invasive Breast Cancer in a Large, Unselected Population, 2000-2006.

Abstract

Abstract BACKGROUND: Most HER2 data have been generated from populations of invasive breast cancer (IBC) patients with selected patient and tumor characteristics (clinical trials, referral centers). The average age of women in US adjuvant trastuzumab trials was 49. Pre 2000, clinical trials of adjuvant chemotherapy included 25-40% HER2+ cases. We used an unselected population of women with IBC to estimate the age-specific incidence rates of HER2+ IBC and compare patient and tumor characteristics of HER2+ and HER2- disease.METHODS: Among female members of Kaiser Permanente Northern California (KPNC) 20 years or older (n=1.22 million), we identified all those diagnosed with a new primary IBC in 2000-2006 (n=16,975). During this period, all IBCs were routinely tested for HER2 by KPNC's regional IHC laboratory (center of excellence for HercepTest, CLIA licensed and CAP certified) and those that were IHC 2+ were sent for FISH testing; IHC 3+ or IHC 2+/FISH+ (ratio ≥ 2.0) were considered HER2+. Demographic and tumor characteristics were derived from the KPNC tumor registry. *Complete HER2 testing available for 94% of IBCs.RESULTS: Incidence of HER2+ IBC increased less dramatically with age and peaked 20 years earlier than incidence of all IBC (Table 1). Among those with IBC, the percent that were HER2+ decreased with age. Of all HER2+ IBCs, 69% were ≥50 years old and 42% were ≥60 years old.Incidence of all IBC and incidence of HER2+ diseaseAge GroupPerson-YrsNo. of IBCsIBC rate/100KHER2+ IBCs*%HER2+HER2+IBC rate/100K20-39288153371024.6416424.75.6940-4917402132680154.0049819.728.6250-5915535284354280.2759914.538.5660-699677624280442.2649412.351.0570-796676013318497.002718.740.5980+3666531633445.381429.638.73ALL817729016975207.59216813.626.51 The percent of tumors that were HER2+ increased with stage (local=11%, regional=18%, distant =25%), tumor differentiation (well =2%, moderate =12%, poor=26%, undifferentiated=30%), and generally with size (<0.5cm=17%, 0.5-0.9cm=7%, 1-1.9 cm=10%, 2-4.9 cm=17%, >5 cm=20%). ER- and PR- tumors were more likely to be HER2+ (of all ER- tumors, 29% were HER2+; of all PR- tumors, 25% were HER2+; of all ER+ tumors, 10% were HER2+; of all PR+ tumors, 9% were HER2+). Among all IBC patients, percent of disease that was HER2+ was highest for Asians (20%) and lowest for Caucasians (12%).CONCLUSION: In a large, unselected, population of invasive breast cancer patients, the incidence of HER2+ disease was highest among women aged 60-69 years. Among breast cancer patients, HER2+ disease was highest in Asians. The percent HER2+ was 13.6% for all breast cancer patients in this population based cohort and highest (24.7%) in the 20-39 year age group. Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 3058.