SIX4 and non-small cell lung carcinoma: The relative expressions of SIX2 and SIX4 were found higher in SQC compared with ADC in NSCLC (SIX2: pooled OR = 0.63, 95 % CI, 0.57–0.70, p = 0.074, and I2 = 45.9 %; SIX4: pooled OR = 0.74, 95 % CI, 0.66–0.82, p = 0.280, and I2 = 19.7 %; Fig. 5a, b).