PMC9742472_01
The pathological analysis, genetic testing, and pedigree of the patient. (A) (a) H&E staining showing a poorly differentiated colonic adenocarcinoma of the primary tissue (x200). (b-e) IHC staining showed MLH1 expression, loss of expression of MSH2 and MSH6, and partly the expression of PMS2 in primary tissue (x200). (B) The pedigree of the patient. The patient was diagnosed with colon adenocarcinoma at 43 years of age. The patient's mother was diagnosed with endometrial adenocarcinoma, gastric adenocarcinoma, and papillary thyroid carcinoma at 40, 61, and 63 years of age, respectively. His grandfather was diagnosed with gastric adenocarcinoma at 40 years of age. (C) The genetic testing result of the patient (a) and his mother (b) by next-generation sequencing revealed a six-base deletion of MSH2 (NM_000251.2: exon 3: c.489_494delTGGGTA).
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American Joint Committee on Cancer (AJCC) staging system. Immunohistochemical analysis of the MMR protein expression showed loss of MSH2 and MSH6 protein expression in the surgical specimen ( Figure 1A ). After four cycles of standard adjuvant chemotherapy (oxaliplatin and capecitabine), the tumor reoccurred in situ quickly, presenting with intestinal obstruction in January 2020. His grandfather was diagnosed with gastric adenocarcinoma at 40 years of age ( Figure 1B ). Genetic testing indicated a germline MSH2 deletion in the reading frame, c.489_494delTGGGTA, resulting in the deletion of two amino acids from 164 to 165 ( Figure 1C ).
The course depicting the treatment process and radiological evaluation from 2019 to 2022. The patient has received pembrolizumab since June 2020, achieving clinical CR after 2 months and has remained in CR until now. AC, adjuvant chemotherapy; CR, complete response; R, recurrence; CT, computed tomography; PET/CT, positron emission tomography/computed tomography.
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The therapy was well tolerated, and the patient has remained progression-free until now ( Figure 2 ).