Margin call: Predicting margin involvement following surgical removal of rectal tumors

This study investigated risk factors for positive circumferential resection margins (CRM) in patients with cancer in the middle or lower rectum.

Locally advanced rectal cancer indicates that the cancer has spread beyond the lining of the rectum or has spread to the nearby lymph nodes. The main treatment for patients with locally advanced rectal cancer is radiochemotherapy followed by total mesorectal excision (TME). TME is a surgical procedure to remove the tumor and a large portion of bowel surrounding it. The combination of TME and radiochemotherapy is generally very successful, with less than 10% of patients experiencing local return of the cancer.

The mesorectal fascia is an area of fatty tissue that holds blood vessels and nerves, and is found surrounding the rectum. Patients whose tumors are within one millimeter of the mesorectal fascia are referred to as having a positive CRM. These patients have worse prognosis, therefore it would be valuable to determine if any factors can predict CRM positivity.

This study included 233 patients who received radiochemotherapy followed by laparoscopic TME (minimally invasive TME) for low or mid rectal cancer. Potential risk factors for positive CRM were investigated including age, cancer positive lymph nodes, cancer in the lower portion of the rectum, T4 cancer (the cancer has grown through the outermost lining of the intestines and may have invaded nearby tissue or organs).

11% of patients (25 patients) had a positive CRM. Statistical analysis found that an initial grade T4 cancer or longer operation times (more than 240 minutes) increased the odds of having a positive CRM. The odds of having a positive CRM was 6 times higher in patients with T4 cancer than for patients with lower cancer grades. The odds of having CRM involvement was 5.4 times higher for patients whose operation took longer than 240 minutes compared to patients with lower operation times.

The risk of positive CRM also increased if patients had more than one of the risk factor (T4 grade and long operation time). 3% of patients with none of the risk factors had positive CRM compared to 10% of patients with 1 risk factor and 38% of patients with 2 risk factors.

The authors concluded that patients with T4 grade rectal cancer and longer operation times seem to be at higher risk for CRM involvement.