Background: Breast cancer incidence in Taiwan is continuous rising to the leading cancer incidence rate in women according to cancer registry. We hypothesize hormone replacement therapy (HRT) or mammography screening affect the breast cancer incidence.

Objectives: 1) To determine whether a similar decline of HRT use and breast incidence occurred in Taiwan. 2) To compare frequency and dose of use HRT with breast cancer incidence. 3) To compare change of mammography rates in different age groups and period of time with breast cancer incidence and mortality.

Methods: Breast cancer incidence in most industry countries declines as HRT use drops. This study analyzed national health insurance data from 2000-2008. Women aged above 40 years who was diagnosis postmenopausal or osteopenic were extracted from database for analysis. This research looked at information from prescriptions for HRT, mammography rates and breast cancer incidence and mortality rates. Approximately 82,478 postmenopausal or osteopenic women were included in this analysis. Odd ratios were derived from nested case control estimation to compare with HRT use, total dose and total duration of HRT. Mammography rates in different age groups and different period of year were compared by using national health insurance data.

Results: We found that a reduced frequency of use of HRT was reflected in the decrease in dispensed HRT prescriptions after 2002 announced be the Women Health Initiative (WHI) in Taiwan. The largest drop in use of HRT occurred between 2002 and 2003 and continuous drop is noted during our study period. Compared with never users, estrogen and progestin users were with higher risk of breast cancer (OR: 1.58, 95% CI 1.16-2.14, p<0.003) and higher among current users of estrogen only (OR: 1.48, 95% CI 1.13-1.93, p<0.004). The HRT use, total dose of HRT and duration of HRT all showed dose-response effects (OR: 2.42 for HRT use more than 30 times; OR: 3.59 for total use of HRT for more than 3 years; OR: 3.18 for duration of use HRT). They are all statistical significant (p<0.001). Compared with mammography rates with different period of time, the study found that nearly 40% rise in breast cancer rates coincided with the 50% increase in mammography rates between 2000 and 2008. The breast cancer incidence increased following by mammography rates inclined, particular in aged 40 to 59 years group during 2001 to 2005 and 2006 to 2010. Breast cancer incidence rates began to increase dramatically in 2006 to 2010 among women aged 40-49 years. Compared with total mortality to incidence ratio [1-(M/I)] (proxy site-specific cancer survival), the survival ratio increased from 74.7% (2000) to 81.3% (2008).

Conclusion: The breast cancer risk was elevated with the use of combined HRT. In Taiwan, breast cancer incidence rates continuous increase among aged 40-59 years, which is likely explained by the promotion of mammography for government breast cancer screening programs from 2003. Mortality to incidence ratio in Taiwan did show some improvement, but still limit. Some argue that the plasticizers - DEHA, DBP, BBP, DEHP, DOP - as estrogen-like substances is the cause which was discovered widely used for food packaging and illegally add into food drink in Taiwan food industry may disturb the endocrine system. Further long-term surveillance studies of time trend and spatial patterns between breast cancer incidence rate and screening rates can help reconcile the potential population-level association of these two factors.

Citation Format: Eng-Mei Tsai, Po-Huang Chiang, Yen-Chen Chang. Does hormone replacement therapy or mammography screening affect breast cancer incidence rates in Taiwan? A nationwide cohort study. [abstract]. In: Proceedings of the Eleventh Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2012 Oct 16-19; Anaheim, CA. Philadelphia (PA): AACR; Cancer Prev Res 2012;5(11 Suppl):Abstract nr B71.