Colorectal cancer is unique in solid tumor oncology because surgical resection for patients with solitary or oligometastatic disease can provide long-term disease-free survival, and even cure. [1][2][3][4][5] Largely predicated on the notion that earlier recurrence detection will allow a greater chance of surgery with curative intent, specialty guidelines recommend that patients with stage II or III colorectal cancers should be followed up with a 5-year surveillance program of carcinoembryonic antigen (CEA) testing, computed tomography (CT) scans, and endoscopy. [6][7][8][9][10] These guidelines are supported by multiple prior studies on the role and schedule of surveillance, which suggest surveillance increases curative intent surgical resections and improves overall survival. 11 However, individual trials have used varied testing schedules, employed suboptimal imaging methods, and have been uniformly underpowered. Thus, the optimal postoperative surveillance strategy and the true effect of surveillance on cancer outcomes remain unknown. The articles in this issue of JAMA by Wille-Jørgensen et al 12 and Snyder et al 13 were both designed to evaluate whether higher-intensity testing (ie, more frequent) is more effective than a lower-intensity surveillance strategy as a means of improving the critical outcomes of recurrence detection and overall survival for nonmetastatic colorectal cancer.The COLOFOL trial by Wille-Jørgensen and colleagues 12 was a randomized trial conducted at 24 centers in Denmark, Sweden, and Uruguay that compared a high-and lowintensity surveillance strategy following surgery and adjuvant therapy (as indicated) for stage II or III colorectal cancer. The high-intensity strategy consisted of CEA testing and CT of the chest and abdomen 6, 12, 18, 24, and 36 months after surgical resection. The low-intensity strategy consisted of CEA and CT at 12 and 36 months. The COLOFOL trial was designed to detect a 6% absolute difference in overall survival between the high-and low-intensity strategies at 5 years with 85% power.The results of the COLOFOL trial were null, with no difference in any clinically meaningful end point reported. The intention-to-treat analysis, including the 2509 randomized patients, found no significant difference in 5-year mortality between patients in the high-intensity surveillance group, 13%, compared with the low-intensity group, 14%, with a risk difference of 1.1% (95% CI, −1.6% to 3.8%, P = .43). A per-protocol analysis excluding patients whose surveillance was not con-