We then assessed RSPO4 promoter methylation using methylation-specific PCR (MSP) and found that RSPO4 promoter was frequently methylated in cell lines of NPC, ESCC, Lung Ca, CRC, Blad Ca and OvCa, well correlated with its expression levels (Fig. 1H and Fig. S1A, Table 2). The gene discussed is RSPO4; the disease is esophageal squamous cell carcinoma.