Our analysis indicated that the mRNA expression of SIX1 (OR: 2.13, 95% CI: 1.28–3.54; P = 0.040 and I2 = 57.0%; Fig. 2A), SIX2 (OR: 1.79, 95% CI: 1.06–2.99; P = 0.444 and I2 = 0.0%; Fig. 2B), SIX3 (OR: 2.04, 95% CI: 1.17–3.56; P = 0.362 and I2 = 6.3%; Fig. 2C), and SIX4 (OR: 5.37, 95% CI: 3.01–9.57; P = 0.776 and I2 = 0.0%; Fig. 2D) was increased in breast cancer tissues when compared with normal breast tissues. This evidence concerns the gene SIX4 and breast cancer.