HOXA9 and non-small cell lung carcinoma: In study group #1, SCLC disclosed significantly higher APC, HOXA9, RARβ2, and RASSF1A promoter methylation levels compared to NSCLC (p < 0.0001 for all genes, except for HOXA9, p = 0.021) (Figure 2A), whereas in ccfDNA (study group #2), only HOXA9 and RASSF1A retained significant statistical differences (p < 0.0001 for both genes) (Figure 2B).