Shiyun Cui1, Xiao Zhang2, Ruihan Zou2, Fan Ye2, Yutong Wang2, Jing Sun3. 1. Department of Oncology, The First Affiliated Hospital of Nanjing Medical University, Nanjing, China, cuishiyun@njmu.edu.cn. 2. The First School of Clinical Medicine, Nanjing Medical University, Nanjing, China. 3. Department of Oncology, The First Affiliated Hospital of Nanjing Medical University, Nanjing, China.
Abstract
INTRODUCTION: Deleterious heterozygous mutation of the MLH1 gene is an important cause of Lynch syndrome (LS), an autosomal dominant cancer caused by functional defects in the DNA mismatch repair (MMR) complex. CASE REPORT: The proband was a 35-year-old patient with confirmed colorectal cancer (CRC). Immunohistochemical (IHC) staining revealed the absence of MLH1 and PMS2 expression in the colorectal tissue specimens of the patient. Genetic counselling and tumor gene testing were performed using next-generation sequencing technology. The genetic tumor verification report showed the deletion of 4 bases in exon 12 of the tested MLH1 gene and a transcoding mutation. To our knowledge, this germline splice site mutation of MLH1 has not been reported before. The proband accepted several therapeutic regimens including PD-1 inhibitor and ultimately died of multiple organ failure. CONCLUSION: Nonsense mutations and frameshift mutations of MMR genes are the most common causes of LS. Common mutations include those in MSH2, MLH1, MSH6, and PMS2. We report a mutation of MLH1 that has never been reported before. We recommend that patients with a history of colon or rectal cancer receive universal MMR or MSI testing and checkpoint inhibitor therapy for the first-line treatment of deficient MMR CRC.
INTRODUCTION: Deleterious heterozygous mutation of the MLH1 gene is an important cause of Lynch syndrome (LS), an autosomal dominant cancer caused by functional defects in the DNA mismatch repair (MMR) complex. CASE REPORT: The proband was a 35-year-old patient with confirmed colorectal cancer (CRC). Immunohistochemical (IHC) staining revealed the absence of MLH1 and PMS2 expression in the colorectal tissue specimens of the patient. Genetic counselling and tumor gene testing were performed using next-generation sequencing technology. The genetic tumor verification report showed the deletion of 4 bases in exon 12 of the tested MLH1 gene and a transcoding mutation. To our knowledge, this germline splice site mutation of MLH1 has not been reported before. The proband accepted several therapeutic regimens including PD-1 inhibitor and ultimately died of multiple organ failure. CONCLUSION: Nonsense mutations and frameshift mutations of MMR genes are the most common causes of LS. Common mutations include those in MSH2, MLH1, MSH6, and PMS2. We report a mutation of MLH1 that has never been reported before. We recommend that patients with a history of colon or rectal cancer receive universal MMR or MSI testing and checkpoint inhibitor therapy for the first-line treatment of deficient MMR CRC.