To circumvent the aneuploidy of chromosomes, we first developed real-time quantitative PCR with a reference gene mapped to the same chromosome, and subsequently showed that the ratio, CCND1 (11q13) / DRD2 (11q22-23), in plasma DNA is a valuable diagnostic tool for detecting cancers, monitoring therapeutic effects and predicting both clinicopathological factors and postoperative prognosis of ESCC patients. The gene discussed is DRD2; the disease is esophageal squamous cell carcinoma.