We profiled gene expression and promoter DNA methylation of RASSF1A, RASSF1C, and RASSF1-AS1 across 11 tumor cell lines, quantified RASSF1A methylation in lung cancer tissues and plasma by quantitative methylation-specific PCR (qMSP), and integrated single-CpG methylation (pyrosequencing) with in silico transcription factor binding site (TFBS) prediction.<h4>Results</h4>We found that RASSF1A promoter hypermethylation was strongly and inversely associated with its mRNA levels. The gene discussed is RASSF1; the disease is neoplasm.