Purpose: The aim of this study was to determine the long-term outcome after curative resection of colorectal cancers that extend only into the submucosa ("minimally invasive") and to evaluate potential histologic predictors of lymph node metastases.
Methods: Seventy-nine patients who underwent curative resection of minimally invasive colorectal cancer and were followed for at least five years were studied retrospectively.
Results: The series was comprised of 53 men and 26 women, with a mean age of 61 years. The lesion was in the colon in 47 patients and the rectosigmoid or rectum in 32 patients. Open surgery followed attempted endoscopic tumor removal in 25 patients. Lymph node metastasis, found in 11/79 patients (13.9 percent), was associated with worse outcome: 36.4 percent of node(+) patients developed recurrence, vs. only 5.9 percent of node(-) patients (P < 0.005). The cumulative survival rate was also worse in node(+) vs. node(-) patients: 72.7 percent vs. 91.1 percent at five years (P < 0.05) and 45.5 percent vs. 65.3 percent at ten years (P < 0.05). Five histopathologic characteristics were identified as risk factors for lymph node metastasis: 1) small clusters of undifferentiated cancer cells ahead of the invasive front of the lesion ("tumor budding"); 2) a poorly demarcated invasive front; 3) moderately or poorly differentiated cancer cells in the invasive front; 4) extension of the tumor to the middle or deep submucosal layer; 5) cancer cells in lymphatics. Whereas patients with three or fewer risk factors had no nodal spread, the rate of lymph node involvement with four or more risk factors was 33.3 percent and 66.7 percent, respectively.
Conclusions: Metastasis is not infrequent in "minimally invasive" colorectal cancer. Appropriate bowel resection with lymph node dissection is indicated if such a lesion exhibits more than three histologic risk factors for metastasis.