Small colorectal cancers resembling submucosal tumor with massive submucosal invasion and lymph node metastasis: A report of two cases and review of the literature.

Colorectal cancer resembling submucosal tumor (SMT) is very rare. We herein report two cases of small colon carcinoma resembling SMT (80-year-old female and 67-year-old male), which massively invaded into the submucosal layer and accompanied marked lymphatic invasion and lymph node metastasis. We also reviewed the reported cases of colorectal carcinoma resembling SMT (SMT-like group, n=70) and analyzed the clinicopathological characteristics of this group compared with typical colorectal carcinoma cases operated at our institution (control group, n=1723). Tumors in the SMT-like group were significantly smaller in size compared with the control group; the median diameter measured 22mm vs. 37mm (P<0.01), respectively. Histologically, although the tumors in the SMT-like group were small in diameter, they almost all invaded into the submucosal (T1) or deeper layer (T2-4), and the rate of poorly differentiated adenocarcinoma or mucinous adenocarcinoma was significantly higher than that in the control group (48.6% vs. 7.7%; P<0.01). In the subgroup analysis of T1 tumors, the rate of lymphatic invasion in the SMT-like group was also significantly higher than that in the control group (43.8% vs. 15.4%; P<0.01). Carcinoma resembling SMT appears to be invasive and has a high risk of lymphatic invasion even if small in size. Therefore, surgical treatment with dissection of the regional lymph nodes might be necessary in cases with any signs of massive submucosal invasion.