Abstract
This is a case of a patient who presented to the emergency department with acute abdominal pain due to bowel obstruction. An extended right hemicolectomy with ileosigmoid anastomosis due to an obstructing mass on the splenic flexure was urgently performed. During operation, liver and peritoneal lesions were detected and samples were also sent for histological analysis. Pathology report was consistent with poorly differentiated mucinous adenocarcinoma with signet ring cells; peritoneal lesions were confirmed histologically as metastatic. Genetic testing revealed the BRAFV600E mutation and mismatch repair deficiency (dMMR). After progressing on 1st line chemotherapy, the patient has a continuing and long-lasting partial response to 2nd line treatment with pembrolizumab.
Highlights
Colorectal cancer (CRC) is the third most common cancer in men and the second in women accounting approximately 1.6 million new cases and 830,000 deaths each year [1]
We describe the case of MSI-H, BRAFV600E mutated, and deficient MMR (dMMR) CRC, which was de novo metastatic to abdominal and supraclavicular lymph nodes with extensive liver disease and who is still on a continuous partial response since starting 2nd line treatment with immunotherapy
We present the case of a patient with mismatch repair (MMR)-D BRAF mutant metastatic CRC who is still responding to immunotherapy, and if progression of disease occurs, she could receive targeted inhibition with BRAF/MEK/antiEGFR or irinotecan/anti-EGFR and vemurafenib
Summary
Colorectal cancer (CRC) is the third most common cancer in men and the second in women accounting approximately 1.6 million new cases and 830,000 deaths each year [1]. BRAFV600E mutation is associated with cyclin D1 activation and microsatellite instability (MSI-H) [5, 7], increased age, performance status 2, and peritoneal metastasis [5] When this mutation is present and there is microsatellite stability (MS-S), it has a negative prognostic value with poor survival [4, 8,9,10,11]. DMMR tumours are associated with high lymphocytic infiltration in the tumour microenvironment, which translates in good responses to immune checkpoint inhibitors. This is supported by a recent phase II study by Le et al showing that response to PD1 inhibitors could be predicted by evaluating the MSI status [19]. We present a case of a patient with de novo metastatic BRAFV600E mutated and dMMR mCRC who has a continuing and long-lasting partial response to 2nd line treatment with pembrolizumab
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