2022 Volume 40 Issue 1 Pages 17-23
For a diagnosis of malignant peritoneal mesothelioma, the tumor must pathologically be shown to have mesothelial cell origin and features of malignancy. Immunohistological methods to demonstrate the former have been largely established; however, methods to determine the latter are as yet unclear. Here we report a case of malignant peritoneal mesothelioma diagnosed by histopathological examination of an excised recurrent lesion. The patient was 52 years old (gravida 0, para 0). She underwent laparotomy for a uterine leiomyoma, and a fragile necrotic mass was found in the Douglas' pouch. Immunostaining of the mass showed no BAP1 loss or MTAP loss, and the mass was diagnosed as mesothelial hyperplasia. The patient returned to our clinic 24 months postoperatively with lumbar back pain. A computed tomography scan revealed findings suggestive of disseminated neoplastic lesions, and an open tissue biopsy was performed. Immunostaining of the excised specimen showed BAP1 loss and MTAP loss, and a diagnosis of malignant mesothelioma-epithelial type was made. Immunostaining based on specific genetic mutations was performed on both specimens, but the results were contradictory. However, considering the similarities in the clinical course and histology of the two specimens, the initial specimen was also thought to be a malignant mesothelioma.
