Complete Response to Pembrolizumab in a Patient With Metastatic Colon Cancer With Microsatellite Instability and a History of Guillain-Barre Syndrome
J Gastrointest Oncol. 2019 Feb;10(1):161-165. doi: 10.21037/jgo.2018.09.19.
A 73-year-old Caucasian female patient was referred to our clinic in March, 2016 for metastatic colon cancer. Her past medical history was significant for history of DCIS treated surgically and in remission since 2011, a diagnosis of pulmonary embolism on maintenance rivaroxaban, and a diagnosis of GBS since 2014. Her GBS occurred after an influenza-like illness and was initially associated with significant neurological deficits which reversed with IVIG treatment. She has been under the care of Neurology service and had been maintained since her GBS diagnosis on IVIG every 4 weeks. Her colorectal cancer history is significant for a right hemicolectomy in February 2015 with a pathological stage T3N2aM0 adenocarcinoma and with a poor differentiation. She received 6 months of adjuvant capecitabine given her limited performance status, neurological history, and easy fatigability. Three months after completion of adjuvant therapy, a whole-body PET/CT scan revealed multiple FDG-avid enlarged retroperitoneal lymph nodes and a 4.7 cm right anterior pelvic mass with a (standardized uptake value) SUV of 24.5. A biopsy of the pelvic mass confirmed metastatic colorectal cancer.
Considering the right sidedness location of primary tumor and co-existing neuropathy, she was offered first-line treatment with folinic acid, 5-fluorouracil, irinotecan (FOLFIRI) and bevacizumab. Unfortunately, the patient developed severe fatigue and lower extremity cellulitis after 2 cycles of systemic chemotherapy, despite considerable dose reductions. In the interim, next generation sequencing (NGS) of her tumor by FoundationOne® (Foundation Medicine, Inc., Cambridge, MA, USA) revealed the presence of a BRAF V600E mutation, MSI, and a high tumor mutation burden (73/MB). Given her intolerance to chemotherapy, we discussed the possibility of treatment with PD-1 inhibitors with maintenance IVIG and counseled her about the possibility of an autoimmune disease flare. The patient consented to treatment and received pembrolizumab intravenously at 200 mg every 3 weeks. From May 13, 2016, to July 06, 2017, she received 20 cycles of pembrolizumab without toxicities except for mild worsening of existing fatigue and increased myalgias. Her GBS continued to be managed by maintenance IVIG every 4 weeks without flares. Surveillance CT scan showed significant and persistent reduction in tumor burden throughout therapy, with complete remission being attained in January 2017 (Figure 1). Pembrolizumab was discontinued in July 2017 following 6 months of complete remission. She continues to be monitored by CT scans and CEA every 3 months and is in full remission as of her last CEA and imaging studies from May of 2018.
