CXCR4 expression was not associated with certain clinical parameters of breast cancer, such as tumor category (T category: T0-2, T3-4) (pooled RR =1.09, 95% CI: 0.80-1.47, P = 0.451 and I2 = 0 fixed-effect), ER status (pooled RR =0.97, 95% CI: 0.97-1.05, P = 0.014 and I2 = 51.3 random-effect), PR status (pooled RR =0.99, 95% CI: 0.87-1.12, P = 0.016 and I2 = 51.5 random-effect), or c-erbB-2 status (pooled RR =1.16, 95% CI: 0.85-1.56, P<0.001 and I2 = 84.9 random-effect) (Figure 2a,d,e,f). The gene discussed is CXCR4; the disease is breast cancer.