Higher incidence of premenopausal breast cancer in less developed countries; myth or truth?

Abstract

Background: Fundamental etiologic differences have been suggested to cause earlier onset of breast cancer in less developed countries (LDCs) than in more developed countries (MDCs). We explored this hypothesis using world-wide breast cancer incidence data.

Methods: We compared international age-standardized incidence rates (ASR) of pre- (<50 years) and postmenopausal (≥50 years) breast cancers as well as temporal trends in ASRs of pre-and postmenopausal breast cancer among selected countries during 1975-2008. We used joinpoint log-linear regression analysis to estimate annual percent changes (APC) for premenopausal and postmenopausal breast cancer in the northern Europe and in Black and White women population in the US.

Results: Premenopausal breast cancers comprised a substantially higher proportion of all incident breast cancers in LDCs (average 47.3%) compared to MDCs (average 18.5%). However, the ASR of premenopausal breast cancer was consistently higher in MDCs (29.4/100,000) than LDCs (12.8/100,000). The ASR of postmenopausal cancer was about five-fold higher in the MDCs (307.6/100,000) than the LDCs (65.4/100,000). The APC of breast cancer in Denmark was substantially higher in postmenopausal (1.33%) than premenopausal cancer (0.98%). Higher incidence of breast cancer among the white than black women in the US was pertained only to the postmenopausal cancer.

Conclusion: The substantial and consistent lower age-specific incidence of breast cancer in LDCs than in MDCs contradicts the theory of earlier onset. Demographic differences with fewer old women in LDCs and lower prevalence of risk factors of postmenopausal cancer are the most likely explanation to the lower mean age at diagnosis in these countries.

Figure 1

Estimated proportions and age standardized incidence rate (ASR) of pre- and postmenopausal breast cancer on a log scale for selected countries in 2008 (GLOBOCAN 2008)[16].

Figure 2

Estimated proportion of Women population in age groups 20–49 and ≥50 from total women population in selected countries in 2005 (United Nations 2012) [[26]].

Figure 3

Premenopausal and postmenopausal breast cancer age standardized incidence rate (ASRs) and percent of premenopausal patients in Denmark from 1943 to 2008.

Figure 4

Trend of pre- and postmenopausal incidence rates of breast cancer during 1975 to 2008. Rates are age-adjusted to the world standard population. Sources: [27,28].