Unusual immunohistochemical “null” pattern of four mismatch repair proteins in gastric cancer: A case report

Figure 1 Pathological characteristics. A: Gross appearance of the tumor; B: Microscopic appearance of the tumor with necrosis; C: Microscopic appearance of the tumor with solid pattern and lymphatic stroma; D: The tumor cells were positive for cytokeratin AE1/AE3 by immunohistochemical staining; E: High expression of PDL1 (22C3) CPS>1; F: Epstein–Barr virus encoded small RNA was negative (figures at 100-200 × magnification).

Figure 2 Expression of mismatch repair-related proteins by immunohistochemical staining. The tumor cells were completely negative for all four proteins. A: MLH1; B: PMS2; C: MSH2; D: MSH6 (all images at 200 × magnification).

Figure 3 Results of next-generation sequencing. The mutation of MSH2 and amplification of PIK3CA were observed.