Clinical subtypes of breast cancer in Thai women: a population-based study of Chiang Mai province

Background: The change over time of distribution of breast cancer subtypes using population-based data has not been reported. Objective: To describe the change over time of the distribution of female breast cancer by clinical subtype among the population in Chiang Mai, Thailand. Methods: Data of breast cancer patients from Chiang Mai Cancer Registry, diagnosed from 2004 to 2013 were combined with immunohistochemical status from medical record, and used to describe the proportions of clinical breast cancer subtypes: (1) luminal A-like (ER+/PR+ and HER2-), (2) luminal B-like (ER+/PR+ and HER2+), (3) HER2 (ER- and PR- and HER2+), (4) triple-negative (ER- and PR- and HER2-). The distribution of breast cancer subtypes by age group was also described. Results: Among 3,228 female breast cancer cases diagnosed during 2004-2013, the median age was 52 years and most patients presented at the regional stage. The unknown tumor subtype was lower than 25% in the periods 2008-2009, 2010-2011, and 2012-2013. In those periods, the proportions of luminal A-like were 33%, 36%, and 48%; the proportions of luminal B-like were 14%, 20%, and 16%, the proportions of HER2 were 15%, 14%, and 13%; and the proportions of triple-negative were 16%, 14%, and 13%, respectively. In comparison with other groups, women aged >= 60 years had a significantly higher proportion of luminal A-like (P = 0.001), while women aged <40 years tended to have a higher proportion of triple-negative (P = 0.10). Conclusions: The proportion of breast cancer with luminal subtypes is increasing. Thus, in the future, treatment protocols with a variety of hormone therapies should be provided in order to improve efficacy and coverage of treatment for this population.