HOXA9 and lung adenocarcinoma: Moreover, Lissa et al. quantified HOXA9 (Homeobox A9) promoter methylation in formaldehyde fixed paraffin embedded (FFPE) samples of stage I lung adenocarcinoma patients by droplet digital PCR-based DNA methylation assay and found that high HOXA9 methylation alone or combined with blood vessel invasion (BVI) could potentially inform a higher risk of aggression or a worse outcome of patients with stage I LUAD [7].