Results from a large retrospective analysis provided support for a significant colon cancer-specific survival benefit of adjuvant radiation therapy in patients with resectable T4 or M0 colon cancer. The findings from this study were published in Radiotherapy and Oncology.
While radiation therapy in the neoadjuvant setting is considered part of the standard of care in the treatment of most patients with resectable, locally advanced rectal cancer, limited data on the use of radiation therapy in the treatment of locally advanced colon cancer either prior to or following surgery have not shown the same degree of benefit. Furthermore, a phase 3 randomized trial designed to compare adjuvant chemoradiation therapy with adjuvant radiation therapy alone in patients with resected T3/T4 colon cancer closed early due to patient accrual issues.
In order to reassess the question of whether patients with resectable, locally advanced colon cancer benefit from radiation therapy, the National Cancer Institute’s Surveillance, Epidemiology, and End Results (NCI-SEER) database was interrogated through 2015. The primary end point was colon cancer-specific survival (ie, time between colon cancer survival and death), and the analysis included patients who had both colon cancer as the primary cancer site and as the documented cause of death.
Secondary end points included overall survival (OS) and 5- and 10-year rates of OS. Of the 21,789 patients with resectable, T4 or M0 colon cancer included in the NCI-SEER database up to and including 2015 who met study specifications, only 1001 (4.6%) received adjuvant radiation therapy.
Five-year rates of OS were 42.8% (95% CI, 0.390–0.465) and 35.7% (95% CI, 0.339–0.376) for the groups receiving radiation therapy vs not, respectively. Corresponding 10-year OS rates were 32.0% (95% CI, 0.282–0.358) and 25.1% (0.232–0.270), with a median OS of 43 months for patients receiving radiation therapy and 34 months for those who did not.
Of note, the benefit of adjuvant radiation appeared to be particularly pronounced in the subgroup of patients with T4, N0, or M0 colon cancer where 5-year OS rates were 70.7% (95% CI, 0.654–0.753) with adjuvant radiation therapy vs 60.7% (95% CI, 0.593–0.620) with no adjuvant radiation therapy.
Following adjustments for gender, age, nodal stage, and cancer grade, it was determined that adjuvant radiation therapy was associated with a significant improvement in colon cancer-specific survival compared with no adjuvant radiation therapy (95% CI, 0.8008-0.9779; P =.0165).
Limitations of this study included its retrospective design, its lack of data on patient performance status whether chemotherapy was administered, and the reasons for administering or withholding adjuvant radiation therapy — as well as the potential for selection bias.
“These data provide impetus for the oncology community to reevaluate the use of radiation therapy in locally advanced nonrectal colon cancer. With advances in systemic therapy long-term survivorship is common and local control with adjuvant radiation therapy will play a more profound role in the definitive treatment of resectable T4 colon cancer,” the study authors concluded.