SIX4 and non-small cell lung carcinoma: The high SIX4 and SIX6 expressions were linked with the greater possibility of LNM in NSCLC (SIX4: pooled OR = 3.07, 95 % CI, 1.60–5.92, p = 0.944, and I2 = 0.0 %; SIX6: pooled OR = 1.22, 95 % CI, 1.00–1.48, p = 0.429, and I2 = 0.0 %; see Additional file 2).