Outcomes of Mixed Pathologic Response in Patients with Multiple Colorectal Liver Metastases Treated with Neoadjuvant Chemotherapy and Liver Resection

Background: Pathologic response to preoperative chemotherapy predicts survival in patients with colorectal liver metastases (CLMs) who undergo hepatectomy. In multiple CLMs, mixed pathologic response, wherein tumors exhibit different degrees of treatment response, is possible. We sought to evaluate survival outcomes of mixed response in patients with multiple CLMs. Methods: We conducted a retrospective cohort study using a single-institution database of patients with two or more CLMs who underwent preoperative chemotherapy and hepatectomy (2010–2018). Pathologic response of each tumor was measured on pathology. Patients were stratified by pathologic response as complete (pCR) = 0–1% viability; major (pMajR) = 2–49% viability; minor (pMinR) = 50–99% viability; or mixed (pMixR) = at least one pCR/MajR tumor and one pMinR. Recurrence-free survival (RFS) and overall survival (OS) were estimated using the Kaplan–Meier method, and adjusted risk of death was evaluated using Cox regression. Results: Among 444 patients, 6% had pCR, 34% had pMajR, 36% had pMinR, and 24% had pMixR. Median and 5-year RFS for patients with pMixR was 10.4 months and 16%, respectively, compared with pMajR (11.3 months and 18%, respectively), pMinR (7.7 months and 13%, respectively), and pCR (23.1 months and 38%, respectively) [log-rank p < 0.001]. Median and 5-year OS for patients with pMixR was 77.4 months and 60%, respectively, compared with pMajR (80.5 months and 63%, respectively), pMinR (49.9 months and 39%, respectively), and pCR (median OS not reached; median follow-up of 37.1 months and 5-year OS of 65%) [log-rank p = 0.002]. pMixR was associated with a 52% risk of death reduction (hazard ratio 0.48, 95% confidence interval 0.30–0.78 vs. pMinR). Conclusions: One-quarter of patients with multiple CLMs have pMixR following preoperative chemotherapy and hepatectomy. OS and RFS for patients with pMixR mirror those of pMajR rather than pMinR, suggesting the greatest response achieved in any metastasis best predicts survival.