A comparison of epidemiology, biology, and prognosis of inflammatory breast cancer in Japanese and US populations

Background The epidemiology of inflammatory breast cancer (IBC) in East Asia has not been fully investigated. We hypothesized the epidemiologic factors associated with IBC in Japanese populations are different from other populations. To determine this, we conducted a comparison study assessing multiple clinically relevant risk factors. Patients and Methods Patients diagnosed with IBC at St. Luke's International Hospital (SLIH) in Tokyo, Japan, and at the University of Texas MD Anderson Cancer Center (MDA) in Houston, Texas, from 2003 to 2009 were identified via the electronic medical records. Stage IV patients were excluded. Epidemiological, biological, and overall survival (OS) data were collected and compared. After all patient populations were combined, Cox proportional hazard regression analysis was performed. Results Twenty-two patients at SLIH and 384 patients at MDA were identified. No differences were found for IBC between SLIH and MDA regarding age at diagnosis (P =.898), hormone receptor status (P =.144), overexpression of HER2 (P =.136), or OS (P =.323), however, BMI (P <.01) and nuclear grade (NG) (P <.01) in Japanese patients were lower than those of US patients. Cox proportional hazard regression analysis revealed ER status and race were associated with OS. Conclusion Despite the small number of patients enrolled, IBC in a Japanese population demonstrated lower BMI and lower NG than IBC in a US population with no difference in survival. ER status and race were prognostic factors when the 2 populations were combined. To more robustly define IBC among East Asian individuals, we have started to register Japanese patients with an International IBC Registry.