Additionally, there was a study on the sputum of lung cancer patients, which successfully identified 4 methylation-related biomarkers, including APC, CDKN2A/p16, HS3ST2 (3OST2), and RASSF1A, and they all can play a part in early screening of lung cancer by serving as biomarkers for early diagnosis [29]. Here, RASSF1 is linked to lung cancer.