The remarkable complete response and improvement of performance status to pembrolizumab of a recurrent microsatellite instability high, metastatic colon cancer, previously treated with Cetuximab, FOLFOX and Irinotecan

Abstract

Background: Pembrolizumab, an anti-Programmed Death 1 (PD-1) inhibitor was recently approved by FDA for Microsatellite instability (MSI) high colorectal cancer. The ongoing phase II study by Le, D. et al noted good clinical outcome of Pembrolizumab on MSI-high advanced colorectal cancer previously treated with fluoropyrimidine, oxaliplatin, irinotecan, bevacizumab, cetuximab or panitumumab. Methods: A 37-year-old male was diagnosed with cecal adenocarcinoma stage IV (liver metastasis), KRAS wild type andNRASwild type. Adjuvant chemotherapy of Cetuximab plus FOLFOXwas initiated. After chemotherapy, follow-upMRI demonstrated a complete response.Disease progression with new liver lesion was found after 3 months of the initial chemotherapy. Subsequent chemotherapy of Irinotecan and 5-FUwas administered, where surveillanceMRI showed complete response after treatment.However, after 6months, a new lesion on the liver was again noted along withmultiple new lymphadenopathies. Immunohistochemistry analysis revealed an MSI-High metastatic liver tumor. Monotherapy of pembrolizumab 200mg every 21 days was then infused. Results: Surveillance MRI and PET CT Scan after 1st cycle of Pembrolizumab noted complete response. The patient is currently on his 4th cycle of pembrolizumab, still with complete response. The performance status of the patient also improved to ECOG Grade 0 from ECOG Grade 1-2 after Pembrolizumab infusion. Conclusions: This case report provides an account of the good response ofMSI-High advanced colorectal cancer on Pembrolizumab. In addition, this shows that improvement in performance status can also be seen in monotherapy of Pembrolizumab. Although not the initial therapy for advanced colorectal carcinoma, pembrolizumabmay be a good initial adjuvant systemic therapy forMSI-High advanced colorectal carcinoma.