RSPO4 and lung cancer: Further RT-PCR analysis showed that RSPO4 was well expressed in immortalized normal cell lines (Fig. 1H), but frequently silenced or downregulated in a variety of carcinoma cell lines including nasopharyngeal cancer (NPC), esophageal squamous cell carcinoma (ESCC), lung cancer (Lung Ca), colorectal cancer (CRC), bladder cancer (Blad Ca) and ovary cancer (OvCa) (Fig. 1H and Fig. S1A).