[Analysis of metastatic patterns after curative colorectal cancer surgery based on primary tumor location]

To evaluate metastatic patterns of colorectal cancer following curative surgery based on primary tumor location in order to provide evidence for the decision of individualized adjuvant therapy and postoperative follow-up.

Clinical and follow-up data of 904 patients who underwent curative colorectal cancer in The Affiliated Tumor Hospital of Zhengzhou University from October 2004 to October 2012 with complete follow-up data were analyzed retrospectively. A total 274 patients belonged to right-sided colon cancer group (cecum, ascending, hepatic flexure, and transverse colon), 243 belonged to left-sided colon cancer group(splenic flexure, descending, and sigmoid colon), and 387 belonged to rectal cancer group. The overall rate of distal metastasis and site-specific metastasis rates (liver, lung, and peritoneum) were compared among these 3 groups.

The cohort patients had a median follow-up of 37(4-122) months, and the median follow-up duration was similar in right-sided, left-sided, and rectal cancer groups with 39(5-119), 39(6-122) and 36(5-121) months(P=0.513). During the follow-up period, 44 patients (4.9%) had local recurrence alone, 137 (15.2%) distal metastasis alone, and 30(3.3%) local recurrence combined with distal metastasis. Compared to right-sided colon cancer group, rectal and left-sided cancer groups had significantly higher overall metastasis rates [23.5% (91/387), 17.3% (42/243) vs. 12.0% (33/274), P=0.000). With respect to specific regions, lung metastasis rate in rectal cancer group was 9.3%, which was significantly higher than that in left-sided(4.5%) and right-sided colon cancer group(2.6%)(P=0.001). Other sites of metastasis did not yield significant differences, including liver(P=0.130) and peritoneum(P=0.858).

Cancer location may be used as a reference of personalized adjuvant therapy and postoperative follow-up surveillance programs. Lower threshold for adjuvant therapy in rectal and left-sided colon cancers, and more aggressive surveillance for lung metastasis by chest X-ray or CT should be considered.