Conditional Survival in Patients with Locally Advanced Rectal Cancer and Pathologic Complete Response: Results from an Observational Retrospective Multicenter Long-Term Follow-Up Study

<b>Introduction/Background</b>: Patients with locally advanced rectal cancer (LARC) with pathological complete response (pCR) after neoadjuvant chemo-radiotherapy (NCRT) are a privileged group because of the favorable progression of their disease. However, their follow-up patterns after surgery are similar to those of other groups with worse prognosis, with the consequent psychological and economic impact. <b>Methods</b>: This is a retrospective observational multicenter study with data obtained from the Spanish Rectal Cancer Project. Patients with LARC who underwent surgery with curative intent after NCRT and achieved pCR were selected. The last follow-up update was conducted in December 2021. A conditional survival model was used to analyze oncological outcomes during follow-up. Recurrence-free survival (RFS) was analyzed for the entire cohort of patients and for those who survived at one, two, and three years. <b>Results</b>: A total of 815 patients from 32 hospitals were included. Their mean age was 65.1 years, and 36.1% of them were women. Of the 815 patients, 35 died or experienced recurrence (local or systemic) in the first postoperative year, and 780 were included in the conditional survival analysis one year after surgery. The probability of RFS at 5 years was 86.5% in the whole cohort and 89.4%, 92.9%, and 95.2% for survivors at one, two, and three years, respectively. The probability of recurrence in these same groups was 6.5%, 4.3%, 1.8%, and 0.6%. <b>Conclusions</b>: Follow-up of patients with LARC and pCR after NCRT followed by surgery could be adapted based on conditional survival data showing that the probability of RFS increases as patients remain recurrence-free, and recurrences more than 3 years after treatment are exceptional.