Second recurrence after R0 resection of recurrent colorectal cancer: patterns and implications for surveillance.

BACKGROUND: Although repeat metastasectomy can improve survival in selected patients with colorectal cancer (CRC), the patterns and timing of second recurrence remain unclear. METHODS: We conducted a multi-institutional study of 365 patients who underwent curative intent (R0) resection for their first recurrent CRC between 2008 and 2020. Timing and site of second recurrence were assessed. The median follow-up duration from resection of the first recurrence was 4.9 years. RESULTS: Second recurrence occurred in 206 of 365 patients (56.4%). The 5-year cumulative incidence remained substantial even among patients with early-stage primary disease: 40.7% for stage I, 47.6% for stage II, 63.1% for stage III, and 71.0% for stage IV. Notably, more than 90% of second recurrences occurred within 2 years after resection of first recurrence, and none occurred beyond 5 years, regardless of primary tumor stage or site of the first recurrence. Among patients with stage I-III disease, 54.9% experienced recurrence at the same site as the first recurrence. R0 resection of the second recurrence was achieved in 50.5% of patients, yielding a 5-year overall survival of 62.5%. CONCLUSIONS: The risk of second recurrence remains consistently high across all primary tumor stages and was concentrated within 2 years after resection of recurrent CRC. Nevertheless, nearly half of patients are amenable to repeat curative-intent resection, leading to favorable long-term outcomes. These findings underscore the need for surveillance strategies explicitly designed to detect second recurrences during this critical early period.