Study characterizes salivary pleomorphic adenomas in aged macaques
Bottom line
A new Veterinary Pathology report describes six pleomorphic adenomas in aged rhesus macaques, adding one of the largest characterizations yet of this salivary gland tumor in the species. The tumors were found in macaques ages 19 to 32 years, were predominantly in males, and were incidental necropsy findings in the submandibular salivary gland, according to the study abstract provided by the journal source. Additional conference material from the same research group suggests these lesions were identified through a long retrospective review of necropsy records and showed epithelial and myoepithelial components on histology and immunohistochemistry, with no evidence of metastasis or vascular invasion in the earlier five-case series. (acvp.org)
Why it matters: For veterinary pathologists, laboratory animal veterinarians, and others working with aging nonhuman primates, the report helps define what appears to be a rare but recognizable benign salivary neoplasm in rhesus macaques. That matters because rhesus macaques are widely used as models for human disease and aging research, and older animals accumulate incidental lesions that can complicate study interpretation. Better characterization of salivary pleomorphic adenoma, including its immunohistochemical profile, may improve differential diagnosis against other salivary and myoepithelial tumors at necropsy or biopsy. (pmc.ncbi.nlm.nih.gov)
What to watch: Watch for the full paper to clarify the complete immunohistochemical panel, lesion distribution, and how the authors recommend distinguishing these tumors from other salivary gland neoplasms in macaques. (acvp.org)
Key facts
- Study type
- Veterinary Pathology report
- Species
- Aged rhesus macaques (Macaca mulatta)
- Case count
- Six pleomorphic adenomas
- Age range
- 19 to 32 years
- Sex distribution
- Predominantly males
- Tumor site
- Submandibular salivary gland
- Finding context
- Incidental necropsy findings
- Tumor type
- Pleomorphic adenoma
A new Veterinary Pathology study is putting a sharper definition around a lesion most veterinary teams working in nonhuman primates may never see, but still need to recognize: salivary pleomorphic adenoma in aged rhesus macaques. According to the journal abstract supplied with the story, the authors gathered six cases affecting macaques 19 to 32 years old, mostly males, with tumors identified incidentally at necropsy in the submandibular salivary gland. (acvp.org)
That rarity is part of the point. Pleomorphic adenoma is the most common salivary neoplasm in people, but it appears uncommon in animals and has only recently been described in rhesus macaques, including a separate recent case report involving the soft palate of a 39-year-old female macaque. Earlier literature on salivary gland neoplasms in nonhuman primates also suggests these tumors are infrequently reported overall, likely in part because many research primates are younger and do not reach ages where spontaneous neoplasia becomes more common. (pubmed.ncbi.nlm.nih.gov)
The new paper builds on work this group had already presented in conference abstracts. In a 2025 ACVP student abstract, investigators reported five salivary pleomorphic adenomas identified across 30 years of historical necropsy records at MD Anderson, in four males and one female aged 24 to 32 years. Those tumors were incidental, measured up to 2 x 1 cm, involved parotid and submandibular glands in that earlier dataset, and were described as encapsulated, densely cellular masses composed of epithelial tubules and acini admixed with polygonal myoepithelial cells in a hyalinized vascular stroma. Immunohistochemistry in that abstract showed diffuse pancytokeratin labeling, variable CK7 and GFAP expression, weak SMA staining in myoepithelial cells, Ki-67 labeling in up to 20% of neoplastic cells, and negative cytomegalovirus staining. (acvp.org)
The publication appears to extend and formalize that earlier work, now reporting six cases rather than five. Based on the abstract supplied with the story, the authors summarize gross, histologic, and immunohistochemical findings and emphasize that these tumors were incidental in aged animals. That fits with what is known about rhesus macaques as aging models: they are among the most widely used nonhuman primates in biomedical research, and age-associated pathology becomes increasingly important as colonies maintain older animals for longitudinal studies. (pmc.ncbi.nlm.nih.gov)
Outside commentary specific to this paper was limited in publicly accessible sources, but the broader literature helps frame its significance. Reviews of salivary gland neoplasms in nonhuman primates describe a small and heterogeneous case base, while the recent soft-palate case report underscores that pleomorphic adenoma can arise in less typical sites and may present clinically when it obstructs local anatomy. In contrast, the newly described cases were incidental, which may mean prevalence is underestimated unless institutions perform systematic necropsy review in aged colonies. That last point is an inference based on the contrast between incidental necropsy findings and the scarcity of published reports. (pmc.ncbi.nlm.nih.gov)
Why it matters: For veterinary professionals, especially pathologists and laboratory animal clinicians, the practical value is diagnostic clarity. Salivary gland masses in macaques are rare enough that a well-described immunohistochemical and morphologic baseline can improve confidence in distinguishing benign pleomorphic adenoma from myoepithelioma, carcinoma ex pleomorphic adenoma, adenocarcinoma, or other salivary lesions. It also adds to the background pathology knowledge needed to interpret findings in geriatric research animals, where incidental tumors can affect study readouts, welfare assessments, and decisions about colony management. (acvp.org)
There’s also a translational angle. Because pleomorphic adenoma is common in human salivary pathology and rhesus macaques are established models for human aging and disease, a better description of spontaneous salivary tumors in macaques could be useful for comparative pathology. Even if these lesions remain uncommon, knowing their expected morphology and marker profile helps avoid over-calling malignancy and supports more consistent case classification across institutions. (pmc.ncbi.nlm.nih.gov)
What to watch: The next thing to watch is whether the full paper establishes a more standardized diagnostic panel for macaque salivary tumors, and whether additional retrospective colony reviews show these lesions are truly rare or simply underrecognized in older nonhuman primates. (acvp.org)