Is the High Proportion of Young Age at Breast Cancer Onset a Unique Feature of Asian Breast Cancer?

Purpose: Women with breast cancer in Asian and Western countries are similar in many respects, but there are also differences, such as in the age at onset and the proportion of breast cancer occurring at younger ages. There is controversy as to whether these differences are due to inter-racial genetic differences or to environmental or other factors.

Methods: Using the Korean Breast Cancer Society's large breast cancer registry, we investigated the causes of Koreans' unique breast cancer characteristics by examining the changes in the incidence and proportion of young-onset breast cancer (YBC) in Korea over time. We analyzed data from 108,894 patients to compare characteristics between patients with YBC and non-YBC. For a subtype analysis, we analyzed data from 85,691 patients from 2000.

Results: Among the 108,894 patients, 17,877 (15.5%) had YBC. The tumors associated with YBC showed aggressive clinicopathologic features. The incidence of breast cancer in Korea has increased over time, and while both YBC and non-YBC increased each year, the increase in non-YBC was more pronounced; thus, the proportion of YBC has decreased over time. By 2020, it appears that the ratio of YBC in Korea will be similar to that in Western countries. The increase in YBC was mainly due to an increase in the luminal A subtype. The incidence of other YBC subtypes did not change over time.

Conclusions: Our data suggest that the current high proportion of YBC is probably not a unique feature of breast cancer in Asia but rather a transient phenomenon. Additionally, our results indirectly suggest that there were different causes for breast cancer in different age groups, suggesting the importance of using different approaches for different age groups to establish policies for preventing breast cancer.