3109 - Survival and Follow-Up Strategies of Watch-and-Wait Patients with a Clinical Complete Response after Selective High-Dose Neoadjuvant Radiotherapy in Rectal Cancer

C. Yang^1,2, P. J. Wei^1,2, Q. X. Wang^1,2, X. Tian^1,2, Z. T. Zhang^1,2, H. Chang^1,2, W. Xiao^1,2, R. L. Li^2,3, R. Zhang^2,4, and Y. Gao^1,2; ¹Department of Radiation Oncology, Sun Yat-sen University Cancer Center, Guangzhou, China, ²State Key Laboratory of Oncology in South China, Guangdong Provincial Clinical Research Center for Cancer, Guangzhou, China, ³Department of Colorectal Surgery, Sun Yat-sen University Cancer Center, Guangzhou, China, ⁴Department of Endoscopy, Sun Yat-sen University Cancer Center, Guangzhou, China

Purpose/Objective(s): High-dose radiotherapy could improve the clinical complete response (cCR) rate of patients with rectal cancer and enable more patients to adopt the strategy of watch-and-wait. We aimed to analyze the survival of patients in a watch-and-wait cohort with selective high-dose neoadjuvant radiotherapy and to present a more efficient follow-up strategy. Materials/Methods: Consecutive rectal cancer patients in a watch-and-wait strategy with a cCR after neoadjuvant chemoradiotherapy (nCRT) between 2011 and 2021 were retrospectively identified. Survivals were calculated using the Kaplan-Meier method, and cumulative incidence of local regrowth was analyzed using the competing risks method. Local regrowth (LR) was defined from the date of decision for watch-and-wait, while other survival outcomes was defined from the date of treatment.
Results: 153 patients were included and irradiated a total prescribed dose of 50 Gy in 25 fractions. 66 (43.1%) of the patients who failed to achieve a cCR after evaluation continued to receive the high-dose radiotherapy, with a median dose of 80 Gy. With the median follow-up time of 62.5 months [95% confidence intervals (CI), 57.3-67.7], the 5-year overall survival rate was 90% (95% CI, 84.7-95.7), and cancer-specific survival (CSS) rate was 93.9% (95% CI, 89.4-98.5). The 5-year disease-free survival rate was 78.1% (95% CI, 71.5-85.4), and the 5-year distant metastasis-free survival rate was 81.7% (95% CI, 75.3-88.6). The 3-year local recurrence-free survival rate was 87.4% (95% CI, 82.2-92.8), and the 2- and 3-year cumulative incidence of LR was 8% and 10%, respectively. The organ preservation rate was 94.8%. Survival and follow-up data of the 34 patients with recurrence or distant metastasis were further analyzed. A total of 18 patients developed LR while 16 patients had distant metastasis without LR, and 64.7% and 76.5% of these patients with disease progression were detected within the first two years and first three years, respectively. 15, 1 and 18 patients were irradiated a total dose of 50, 37.5 (5 Gy × 5) and 66–80 Gy, respectively. Disease progression within three years was associated with worse CSS (P = 0.031). No significant difference was found in CSS between patients receiving salvage treatment within versus more than two months. With reference to the standard post-treatment follow-up schedule, we calculated the time interval between the standard and the actual follow-up time of patients, which was recorded as the delayed follow-up time. There was no significant difference in groups whenever the cut-off value of the delayed follow-up time was 1, 3, 4 or 12 months (P = 0.479, P = 0.172, P = 0.074, P = 0.460, respectively).
Conclusion: nCRT with selective high-dose radiotherapy in rectal cancer patients with watch-and-wait strategy reveal quite satisfactory survival outcomes, with lower rates and later appearance of local recurrence and distant metastasis. Therefore, there may be a shift towards a less intensive follow-up strategies for these patients.