Incidence Rates of Invasive Breast Cancer in Postmenopausal Women with and without a Family History of Breast Cancer and Stratified by Breast Cancer Risk Score.
Authors: Mitchell B. , Ni X. , Wickerham D. , Sontag A. , Muram D. 
Published: December 2010

Background: Health care professionals often consider family history the most important indicator of invasive breast cancer (IBC) risk and may assume women without a family history of breast cancer (FHBC) are at low risk for IBC. This analysis compared the incidence of IBC in postmenopausal women (PMW) with and without FHBC who were enrolled in the placebo arms of 2 clinical trials.Materials and Methods: The study population for this analysis was PMW with osteoporosis or women with or at high risk for coronary artery disease (CAD). The breast cancer risk (BCR) score [or absolute risk] was calculated using the breast cancer risk assessment (BCRA) tool from the National Cancer Institute (NCI). Descriptive statistics (eg, mean age, BCR score) were calculated for women with or without FHBC. The BCR score was binned into unit intervals and, within each unit, the number of patients, number of IBC cases, and the IBC incidence rates were calculated.Results: Of the 6322 patients included in this analysis (excluding patients ≥86 years old, or with a history of ductal carcinoma in situ or lobular carcinoma in situ), 92 developed IBC (Table 1). For PMW with FHBC [164;12.9%], the mean (±SD) age was 71.3±6.9, the mean BCR score (%) was 3.65±1.09, and all 164 (100%) had a BCR score ≥1.66%, which is consistent with the NSABP Breast Cancer Prevention Trial's definition of “high risk.” For women without FHBC, the mean age was 70.8±6.7, the mean BCR score was 1.74±0.44 and 598 (55.1%) women belonged to the high risk group. For women with or at high risk for CAD and FHBC [443; 8.8%], the mean age was 68.9±6.8, the mean BCR score was 3.52±1.25, and 441 (99.5%) were in the high-risk group. Among women without FHBC (n=4589), the mean age was 67.3±6.6, the mean BCR score was 1.54±0.40, and 1605 (35.0%) were at high risk for IBC. The incidence rate of IBC increased as the absolute risk of breast cancer increased or if FHBC was present, more IBC cases were recorded in women with a lower absolute risk of breast cancer or without a FHBC (Figure 1).Discussion: In general, incidence rates of IBC correlated with BCR estimates and incidence rates were higher as BCR scores increased. However, the majority of women who developed breast cancer had scores between 1% and 2% and did not have FHBC (76/92; 82.6%); many women with IBC (40/92; 43.5%) had BCR scores below the defined high risk cutoff of 1.66%.Total number of all patients, IBC cases and incidence rates grouped by unit BCRA tool score intervalsBCRA Tool Score (%)No. PatientsNo. IBC CasesIBC Incidence Rate(0,1]36610.52(1,2]4602602.61(2,3]881163.74(3,4]369116.28(4,5]35  (5,6]27215.81(6,7]21  (7,8]18222.9(8,9]1  (9,10]1  (10,11]   (11,12]1  Total632292  Figure 1: Invasive breast cancer cases and incidence rate by unit BCRA tool risk intervals. The number of cases represented by the black and gray bars are stacked and not additive.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 6066.