Meningioma, a tumor arising from the meninges—the protective membranes enveloping the brain and spinal cord—is the most frequently diagnosed intracranial neoplasm in dogs, accounting for roughly half of all canine primary brain tumors. In humans, meningiomas represent approximately 40 percent of primary brain tumors. Despite this shared prominence, diagnostic criteria for canine meningioma have remained poorly codified, and until now no study had subjected a large cohort of canine cases to standardized review by a panel of multiple pathologists working alongside physician neuropathologists.

The CBTC board, which brought together veterinary pathologists and human neuropathologists from institutions across the United States and Europe, undertook a comprehensive evaluation of 190 cases of canine meningioma. Tumors were collected from the diagnostic archives of ten veterinary schools, including Auburn, Colorado State, Cornell, Mississippi State, Ohio State, Texas A&M, UC Davis, Illinois, Penn, and Virginia Tech. Samples came exclusively from treatment-naïve patients, prioritized when collected within the previous five years and accompanied by clinical follow-up data such as tumor location, therapy, progression, and cause of death. Histology slides were cut at four micrometers, stained with hematoxylin and eosin, and digitally scanned at 40X resolution, allowing every reviewer to examine identical digital images.

To enable direct comparison with human medicine, the board applied the 2016 World Health Organization classification and grading guidelines for human meningioma to each canine tumor. Reviewers assessed histologic subtype, mitotic count within a fixed region of 2.37 square millimeters, invasion into surrounding nervous tissue, geographic coagulative necrosis, and the atypical features used in human grading: sheeting architecture, small-cell formation, hypercellularity, and macronucleoli. The process began with a virtual meeting in October 2020 to familiarize the physician neuropathologists with canine histology, followed by additional consensus sessions to resolve difficult diagnostic calls before a final independent assessment of all cases by October 2021.

The results demonstrated that canine meningiomas mirror the morphologic diversity of the human disease. The overwhelming majority of tumors—140 of 190, or roughly 74 percent—were classified as meningothelial, with transitional, microcystic, psammomatous, rhabdoid, fibrous, metaplastic, clear cell, and chordoid subtypes making up the remainder. Most cases, 109 tumors or 57 percent, were assigned grade 2 under the human WHO scheme, while 79 were grade 1 and only two reached grade 3. Roughly 60 percent of tumors with assessable adjacent brain or spinal cord tissue showed invasion into the nervous system, and features such as necrosis, sheeting, and hypercellularity were commonly observed, closely paralleling the histologic picture of atypical human meningioma.

Yet the clinical correlation told a more complicated story. Among the subset of patients with detailed progression and cause-of-death information, and again in a larger cohort restricted to live/dead status, there was no statistically significant difference in outcome between grade 1 and grade 2 canine tumors. Relative risk ratios for death at one, two, and three years after diagnosis—0.75, 0.93, and 1.02 respectively—were all statistically insignificant. This challenges the assumption that the human WHO grading framework, which strongly predicts recurrence and progression in people, can be transplanted wholesale to veterinary patients. Several features that signal higher grade in humans, notably macronucleoli and small-cell formation, appeared frequently even in grade 1 canine tumors, and medical pathologists on the board repeatedly observed that macronucleoli occur more often in canine tumors regardless of grade.

One feature did emerge as potentially meaningful: necrosis. Although many progressing tumors lacked necrosis, every case in the outcome-linked subset that did exhibit necrosis went on to show clinical progression, compared with 57 percent of cases lacking it. The authors suggest that necrosis, when present, may be a significant indicator of more aggressive behavior and a critical feature for future prognostic studies. Brain tumors were also significantly more likely than spinal tumors to show necrosis. Notably, the study echoes a shifting paradigm in human medicine, where tumors showing brain invasion without other atypical features—so-called brain-invasive, otherwise benign tumors—now benefit from additional molecular testing, suggesting that molecular characterization could likewise improve prognostication in dogs.

The review also shed light on the reproducibility of diagnosis across specialists. Interobserver agreement, measured by intraclass correlation coefficients, was generally low for most histologic features, with the highest agreement—0.44 for both—achieved for necrosis and CNS invasion, the same features that command the highest concordance in human meningioma review. Concordance exceeded 70 percent for most histologic subtypes, especially those with distinctive appearances such as clear cell and microcystic tumors, while mitotic counting proved the least reliable. Interestingly, veterinary pathologists agreed with one another significantly more often than physician neuropathologists on histologic subtype, hypercellularity, and macronucleoli, suggesting that species-specific experience is critical for diagnostic consistency.

Clinically, the cohort reflected established patterns of canine disease. The median patient age was ten years, and mixed-breed dogs, Golden Retrievers, Labrador Retrievers, Boxers, and West Highland Terriers were the most commonly represented breeds. Most tumors arose over the brain, particularly the olfactory and frontal lobes, with a smaller proportion in the cervical spinal cord. Surgery remained the mainstay of treatment, with a median survival of 437 days for dogs treated surgically, while dogs receiving surgery combined with radiation or other adjuvant therapies survived longer on average, at 28 to 55 months, consistent with previously reported ranges.

The CBTC board concluded that while canine and human meningioma share important histologic features, a revised grading framework specific to dogs is needed, distinct from the human WHO scheme. The consortium recommends that future studies include review of all slides by at least three pathologists, systematic evaluation of location, subtype, mitotic count, invasion, necrosis, and other atypical features, and enrollment limited to cases with complete clinical follow-up. The authors also call for the kind of large-scale, shared cancer databases in veterinary medicine that exist in human oncology, and note that molecular characterization, transcriptional profiling, and immune landscape studies of related canine tumor collections are already underway. If successful, these efforts could position the canine patient as a genuinely translational model—accelerating biomarker discovery and therapeutic development for both dogs and the humans who love them.

Subject of Research: Comparative pathology of canine and human meningioma and the validation of dogs as a naturally occurring model for human meningioma research

Article Title: A comparative evaluation of canine meningioma supporting the canine patient as a naturally occurring animal model for human meningioma: a report from the NCI Comparative Brain Tumor Consortium (CBTC) meningioma pathology board

Article References: Church, M. E., Rissi, D. R., Koehler, J. W., Miller, A. D., Beck, J. A., Belluco, S., Bitar, M., Chkheidze, R., Corps, K. N., Matiasek, K., Phillips, J. J., Rajan, S., Stemmer-Rachamimov, A., Yip, S., Shih, J. H., Mazcko, C., & LeBlanc, A. (2026). A comparative evaluation of canine meningioma supporting the canine patient as a naturally occurring animal model for human meningioma: a report from the NCI Comparative Brain Tumor Consortium (CBTC) meningioma pathology board. Veterinary Oncology, 3(1), Article 16. https://doi.org/10.1186/s44356-026-00068-1

Image Credits: AI Generated

DOI: 10.1186/s44356-026-00068-1

Keywords: meningioma, canine, comparative oncology, brain tumor, WHO grading, pathology, NCI Comparative Brain Tumor Consortium, veterinary oncology, CNS invasion, tumor necrosis, animal model, One Health