Long-term survival of a patient with microsatellite-stable refractory colorectal cancer with regorafenib and PD-1 inhibitor sintilimab: a case report and review of literature.

BACKGROUND: Colorectal cancer (CRC) is the third most prevalent cancer worldwide and poses a serious challenge for clinicians. Previous studies have shown promising results in patients with Microsatellite Stable microsatellite-stable CRC refractory to chemotherapy upon treating with (Programmed Cell Death Protein 1) PD-1 inhibitor combined with regorafenib. Herein, we report a unique case of a patient for whom the conventional chemotherapy and radiotherapy were ineffective, but showed a prolonged stable disease with third-line treatment with regorafenib and PD-1 inhibitor, sintilimab. CASE PRESENTATION: A 64-year-old East Asian female patient was admitted to a regional cancer hospital presenting with abdominal unease due to increased stool frequency and bloody stool. Digital anal examination revealed adenocarcinoma, while genetic profiling of the tumor resections detected wild-type KRAS mutations in codon 12 and 13. Microsatellite instability (MSI) analysis for detecting germline mutations of (Mismatch-repair) MMR genes showed stable phenotype. In December 2016, Miles' resection for intestinal adhesion release and iliac vessel exploration in the rectum was performed (Tumor, Node, Metastasis [TNM]: T3N0M0; stage IIA). The adjuvant chemotherapeutic regimen consisted of a combination of capecitabine at 1.5 g (twice daily) and oxaliplatin therapy at 200 mg for three cycles from February 2016; followed by administering capecitabine tablets orally (1.5 g bid) for five cycles as post-operative palliative care. The patient tested positive for hepatic C virus, which was managed by oral antiviral agents. Following recurrence of rectal adenocarcinoma after 4 years and disease progression with a previous chemotherapeutic regimen, regorafenib was administered at 120 mg once daily combined with sintilimab 200 mg, and the patient's progress was monitored. A follow-up computerized tomography imaging in March 2020 showed disease progression, additionally presented nodule formation (TNM: T3NxM1b; stage IVB). According to Response Evaluation Criteria in Solid Tumors criteria (RECIST), the patient showed a complete response (CR) after treatment with regorafenib and sintilimab immunotherapy. CONCLUSION: Data from this clinical case report support future exploration of combination treatment of the oral multi-kinase inhibitor regorafenib with PD-1 targeted monoclonal antibodies in patients with metastatic microsatellite-stable CRC.