AIM: To investigate the histopathological and geneticdifferences between polypoid growth (PG) and nonpolypoid growth (NPG) submucosal invasive colorectal carcinoma (CRC).METHODS: A total of 96 cases of submucosal CRC were divided into two groups according to their growth type;60 cases of PG and 36 cases of NPG. The size, histological degree of dysplasia, depth of submucosal invasion and lymph node metastasis were compared between the two groups. Furthermore, expression of p53 was detected by immunohistochemical staining, and K-ras gene mutation was examined by polymerase chain reaction based single-strand conformation polymorphism (SSCP).RESULTS: The average size of the lesions in the NPG group was significantly smaller than those in the PG group (7.5 mm vs 13.8 mm, P ＜ 0.001). The histological degree of dysplasia tended to be more severe in NPG group, while the incidence of submucosal massive invasion and the lymph node metastasis were both significantly higher in the NPG type than in the PG group (64.3% vs 43.3%, P = 0.004; 43% vs 7%, P =0.008, respectively). In addition, K-ras gene mutations were detected in 67% of lesions in the PG group, but none in the NPG group, while no difference in p53immunohistochemical expression was found between the two groups.CONCLUSION: Compared with PG submucosal CRC,NPG type demonstrates more frequent submucosal massive invasion, more lymph node metastasis and a higher degree dysplasia. Genetically, NPG type shows much less frequent K-ras mutation.