HBG2 and neoplasm: Methemoglobin levels ≥ 20 ng/ml (HR, 2.227; 95% CI 1.513–3.278; p < 0.001), low to moderate tumor differentiation (HR, 1.625; 95% CI 1.150–2.297; p = 0.006), tumor size > 5 cm (HR, 2.237; 95% CI 1.130–4.429; p = 0.021), and tumor multiplicity (HR, 2.021; 95% CI 1.265–3.228; p = 0.003) were independent risk factors associated with OS.