SMAD4 and cancer: Comparing the mutation status of cancer critical genes in PUMC-CRC1 with that in 19 commonly-used CRC cell lines, it was proved that PUMC-CRC1 with APC (p.T1493fs), KRAS (p.G12V) and SMAD4 (p.V506A) mutations was a unique MSS CRC cell line (Table 3).