POLD4 and neoplasm: MtDNA-CN correlated only with POLD4 expression and showed no association with other selected DNA repair genes (see Additional Table 7), mtDNA damage (Kendall correlation test, τ = −0.06, FDR = 0.457), or patient characteristics such as sex, age, BMI, tumor location, TNM stage, tumor grade, or OS (all FDR > 0.05).