Immunohistochemical evaluation of microsatellite instability in resected colorectal liver metastases: a preliminary experience.

In this retrospective study, we evaluated the predictive role of different immunohistochemical expression (IHC) of the mismatch repair proteins (MMR) in patients with colorectal liver metastasis (CRLM) submitted to liver resection. A total of 108 patients were retrieved, and 15 patients were excluded from the study because of the impossibility to obtain adequate formalin-fixed tissue blocks. The final analysis included 93 patients. Twenty-eight cases (30%) presented a no loss of expression or microsatellite stability (MSS) status, 59 cases (63%) showed a hybrid loss of expression, while 6 cases (7%) presented a complete loss of expression or microsatellite instability status (MSI). Patients with complete or hybrid loss of expression of MMR developed a high intra-hepatic recurrence rate compared to other ones (54% vs 21% OR of 4.278, 95% CI 1.53-11.93) (p = 0.004). The same difference in terms of liver recurrence has been found among patients with R0 resection (50% vs 17% OR of 0.2, 95% CI 0.06-0.65) (p = 0.005). However, there was no difference in terms of disease-free survival and overall survival. Complete or hybrid loss of expression of MMR could be considered a risk factor for intra-hepatic recurrences after liver resections for CRLM.