Trends in Primary Surgical Resection and Chemotherapy for Metastatic Colorectal Cancer, 2000-2016

Background:When, whether, and in whom primary tumor resection (PTR) for patients with metastatic colorectal cancer (CRC) is indicated remains unknown. With advances in multiagent systemic chemotherapy, PTR may be undertaken less frequently. The aim of this study was to obtain estimates of changes in the utilization of PTR and chemotherapy for metastatic CRC.Methods:Patients diagnosed with metastatic CRC between 2000 and 2016 were identified from Surveillance Epidemiology, and End Results (SEER) registry. Multivariable logistic regression defined odds of undergoing PTR. The analysis was also stratified by primary site (colon vs. rectum), age (younger than 50 vs. 50 y and older), and whether patients also underwent resection of metastatic sites (yes vs. no). The secondary endpoint of interest was the receipt of any chemotherapy, also assessed by multivariable logistic regression.Results:Among 99,835 patients with metastatic CRC, 55,527 (55.7%) underwent PTR. The odds of undergoing PTR decreased with a later year of diagnosis, with patients diagnosed in 2016 being 61.1% less likely to undergo surgery than those diagnosed in 2000 (adjusted odds ratio=0.39, 95% confidence interval: 0.36-0.42, P<0.0001; absolute percentage: 62.3% to 43.8%). Similar trends by year for PTR were observed among each of the subgroups, although patients with colon primary, young adults (age younger than 50 y), and patients also undergoing metastasectomy were more likely to undergo PTR (P<0.001 for all). In contrast, the odds of receiving chemotherapy increased dramatically with a later year of diagnosis (adjusted odds ratio=2.21, 95% confidence interval: 2.04-2.40, P<0.0001).Conclusions:From 2000 to 2016, there was a sharp decline in the rate of PTR for patients with metastatic CRC, while the use of chemotherapy increased over the same period. Prospective studies are needed to define the optimal local treatment for patients with metastatic CRC.