The threshold of ACE2 high-low expression [Figure 1(a)] was established by k-means clustering method (detailed in section ‘Methods’) and identifies low- and high-ACE2 expression groups in normal lung of our patients with NSCLC that were surgically resected (p = 1.55 × 10−19) [Figure 1(b)], outlining the significant variations of ACE2 expression levels (low versus high) between individuals, which theoretically may be used to identify patients at low or high risk of developing a severe form of COVID-19. The gene discussed is ACE2; the disease is COVID-19.