SMAD4 and cancer: Comparing the mutation status of cancer critical genes in PUMC-CRC1 with that in 19 commonly-used CRC cell lines, PUMC-CRC1 was a unique cell line with APC (p.T1493fs), KRAS (p.G12V) and SMAD4 (p.V506A) mutations, which enriches the diversity of CRC cell lines.