Performance of the IBIS/Tyrer-Cuzick (TC) Model by race/ethnicity in the Women’s Health Initiative.

Abstract

1503 Background: The TC model, a breast cancer (BC) risk assessment tool based on family cancer history, reproductive and lifestyle factors is used to guide BC screening and prevention. TC was developed and validated largely in non-Hispanic White (NHW) women. We evaluated the calibration and discrimination of TC version 7.02 among racially/ethnically diverse post-menopausal women enrolled in the Women’s Health Initiative (WHI) clinical trials or observational study. Methods: WHI enrolled post-menopausal women from 1993-1998 and followed them prospectively for BC incidence. We included women aged ≤80 years at enrollment with no prior BC or mastectomy and with data required for TC, including weight, height, ages at menarche, first birth and menopause, menopausal hormone therapy use and family history of breast or ovarian cancer in first or second-degree relatives. Calibration was assessed by the ratio of observed BC cases to the number expected by TC (O/E), with expected cases calculated as the sum of cumulative hazards. We tested for differential discrimination by race/ethnicity (NHW, African American, Hispanic, Asian/Pacific Islander, Native American, other) using Cox regression. Time to BC was modeled using age, race/ethnicity, TC estimate (transformed by log of relative lifetime risk), and a term for interaction between race/ethnicity and TC estimate. Results: During the follow-up period (median 18.9 years, maximum 23.4 years), 6,836 new BC cases were diagnosed among 91,893 women. TC was well-calibrated overall (O/E 0.95) in NHW and African Americans, but over-estimated risk for Hispanics (O/E 0.75, Table). Results suggested good calibration for Asian/Pacific Islanders and Native Americans, but sample sizes were small. Discrimination did not differ significantly by race/ethnicity (two-sided p-value for interaction = 0.33). Conclusions: TC provided similar risk discrimination among post-menopausal women of different racial/ethnic groups over nearly 20 years of follow-up; however, it overestimated risk for Hispanics. Future studies in diverse populations are warranted, with need for a more accurate breast cancer risk assessment tool for Hispanics. [Table: see text]