Primary tumor resection (surgical removal of the original tumor) does not improve survival compared with chemotherapy in patients with metastatic colon cancer, according to the results of an observational cohort study.

The study, “Comparative Effectiveness Of Primary Tumor Resection In Patients With Stage IV Colon Cancer,” was conducted at the University of Texas Health Science Center and published in the journal Cancer.

“Although the safety of combination chemotherapy without primary tumor resection (PTR) in patients with stage IV colon cancer has been established, questions remain regarding a potential survival benefit with PTR,” Dr. Zeinab Alawadi, MD, and colleagues wrote, according to a press release. Earlier studies have suggested a causal relation between surgical removal of the primary tumor and improved survival, but the researchers advise caution when interpreting this data, since patients who undergo surgery are those with better performance status.

The goal of this study was to compare the mortality rates of colon cancer patients with inoperable metastasis who underwent surgery to remove their primary tumor compared to those who did not.

Using data from the National Cancer Data Base (2003-2005), the team identified 15,154 patients diagnosed with metastatic colon cancer, 57 percent of whom had surgery to remove the primary tumor. In these patients, most surgeries (approximately 82 percent) were performed within 30 days after the diagnosis. Twenty-five percent of the patients did not undergo chemotherapy.

The team observed that the use of different statistical tests provided opposite results. Some statistical tests indicated that surgical removal of the tumor was associated with a significant reduction in mortality and survival benefit, other tests — which may have a certain bias in the analysis — showed that this treatment did not improve survival.

“By using standard statistical risk-adjustment methods, which inadequately account for confounder effects, (surgical removal of the tumor) appeared to be associated with a significant reduction in mortality,” the authors wrote. “However, instrument variable analysis to control for treatment selection and survivor time bias at the 1-year landmark demonstrated that (surgery) was not associated with a survival benefit over systemic chemotherapy.”

These results note that analyses of data from cancer patients must be done with caution and take into account possible errors and biases, as these can contribute to incomplete conclusions.

Based on their results, the researchers believe that routine surgical removal of the primary tumor is not recommended in colon cancer patients with inoperable metastasis.

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