Molecular Subtypes of Breast Cancer Emerging in Young Women in Taiwan: Evidence for More Than Just Westernization as a Reason for the Disease in Asia

Background: In the past two decades, the incidence of breast cancer in young Taiwanese females has been rapidly increasing, approaching the risk level of western countries. As a first step to investigate the possible etiology, we examined the molecular subtypes of female breast cancer in Taiwan. Methods: This study included 1,028 consecutive patients with breast cancer diagnosed in National Taiwan University Hospital between 2004 and 2006. Estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor-2, cytokeratin 5/6, and epidermal growth factor receptor expression and/or gene amplification were analyzed. Results: Younger (<= 50 years) breast cancer patients had a higher prevalence of luminal A (67% versus 57%; P < 0.001) and a lower prevalence of basal-like subtype (9% versus 17%; P < 0.001) compared with older (>50 years) patients. The higher prevalence of luminal A subtype was mainly attributed to a higher ER (75% versus 63%; P < 0.001) and PR (47% versus 33%; P < 0.001) expression rate in younger patients than older patients. Tumors with histologic grade 3 were less prevalent in younger patients than in older patients (23% versus 30%; P = 0.01). For very young (<35 years) patients, the molecular subtype distribution, ER and/or PR expression rate, and histologic grade were not significantly different from those of less young (35-50 years) patients. Conclusions: Young breast cancer patients in Taiwan are characterized by a high prevalence of luminal A subtype and low prevalence of histologic grade 3 tumor and/or basal-like subtype. These features are distinct from young breast cancer patients in western countries. (Cancer Epidemiol Biomarkers Prev 2009;18(6):1807-14)