NEOPLASIA AND PROLIFERATIVE LESIONS IN FREE-RANGING MOUNTAIN AND GRAUER'S GORILLAS (GORILLA BERINGEI)

There are no published data on the occurrence of neoplasia in wild great apes of any species. The aim of this study was to utilize postmortem and histopathology reports collected from wild human-habituated mountain gorillas (Gorilla beringei beringei) and Grauer's gorillas (Gorilla beringei graueri) to determine both the incidence and types of spontaneous neoplasms and proliferative lesions that occur in these species. Pathology records of 194 mountain gorillas and 12 Grauer's gorillas necropsied from 1985 to 2020 were examined for all cases of neoplasia or hyperplastic/proliferative disease. Slides and/or scanned images were reviewed to confirm morphologic diagnoses. Data were collected on comorbidities that may have contributed to neoplastic/proliferative transformation. A total of nine malignant neoplasms were identified: large cell anaplastic B-cell lymphoma, gastric adenocarcinoma (two cases), gastric carcinoid, oral mucocutaneous malignant melanoma, gastric carcinoma in situ (two cases), squamous cell carcinoma of the lip, and renal adenocarcinoma. Benign lesions included pheochromocytoma, adrenocortical adenoma (two cases), parathyroid adenoma, mandibular fibroma with gingival hyperplasia, and uterine hemangioma. Proliferative gastritis was commonly identified secondary to gastrointestinal parasitism (n = 35); chronic inflammation from nematodiasis may have led to neoplastic transformation of hyperplastic mucosal epithelium. Other hyperplastic lesions included nodular hyperplasia of the adrenal cortex (n = 9), adrenal medulla (n = 7) and thyroid glands (n = 3), pulmonary reactive lymphoid hyperplasia in infants and juveniles (n = 16), as well as nodular splenic siderofibrosis (n = 5) that may be associated with parasite migration. These findings demonstrate that free-ranging mountain and Grauer's gorillas in a natural environment develop neoplasia and proliferative disease.