Clinical significance of metastasectomy and pathological response to pembrolizumab in mismatch repair-deficient metastatic colorectal cancer: A retrospective multi-institutional study

Abstract Background: Metastasectomy is an important treatment to improve survival outcomes in metastatic colorectal cancer (mCRC). However, the evidence regarding the significance of metastasectomy in selected patients with tumors deficient in mismatch repair (dMMR) has been lacking. We aimed to describe the significance of metastasectomy in patients with dMMR mCRC, and the pathological complete response (pCR) rate of patients who underwent metastasectomy after pembrolizumab treatment. Methods: This retrospective analysis included 42 patients with dMMR mCRC treated at Niigata University Medical and Dental Hospitaland its affiliated hospitals. Clinicopathological characteristics, including metastasectomy, were analyzed to evaluate overall survival (OS). Moreover, pCR rate after pembrolizumab treatment was evaluated in patients who underwent metastasectomy. Results: The sites of metastases were lymph node in 17, peritoneum in 16, and liver in seven patients. Metastasectomy was performed in 18 (43%) of the 42 patients. The five-year OS for patients who underwent metastasectomy was 100%, and metastasectomy was an independent prognostic factor for OS (P = 0.009). Three patients underwent metastasectomy with curative intent after pembrolizumab treatment, and pCR was achieved in all three patients (100%). Conclusions: For this small retrospective study, the data suggest that metastasectomy is an important treatment for patients with dMMR mCRC, and patients treated with pembrolizumab show an excellent pCR rate.