Cytomorphological features of canine ocular melanoma: A case series
Bibliographic record
Abstract
An estimated 68 to 82% of primary intraocular tumors in dogs are melanocytic in origin, yet the Cytomorphological spectrum of these neoplasms has received limited systematic characterization in the veterinary literature. This research presents a case series documenting the Cytomorphological features observed in fine needle aspiration cytology (FNAC) specimens from 52 canine ocular melanoma cases diagnosed at a Canadian veterinary pathology referral center over a 36-month period. Dogs of 14 different breeds were represented, with ages spanning 3 to 16 years and a median of 10.1 years. Each specimen was evaluated for a standardized panel of 12 Cytomorphological parameters including cell shape, nuclear-to-cytoplasmic ratio, melanin pigment density, nucleolar prominence, mitotic activity, cell cohesion patterns, cytoplasmic vacuolation, nuclear membrane irregularity, chromatin texture, multinucleation, intranuclear inclusions, and background characteristics. Six distinct morphological patterns were identified: epithelioid (n=18, 34.6%), spindle cell (n=12, 23.1%), mixed epithelioid-spindle (n=8, 15.4%), balloon cell (n=6, 11.5%), signet-ring (n=4, 7.7%), and amelanotic (n=4, 7.7%). Epithelioid melanomas characteristically exhibited large round to polygonal cells with eccentric nuclei, prominent nucleoli, and moderate to heavy cytoplasmic melanin granulation. Spindle cell variants displayed elongated fusiform cells arranged in loose fascicles with tapered cytoplasmic processes and variable pigmentation. Balloon cell melanomas were distinguished by markedly expanded pale cytoplasm with peripheral melanin displacement and centrally placed small nuclei. The signet-ring pattern, less commonly described in veterinary cytology, featured cells with a single large cytoplasmic vacuole displacing the nucleus peripherally, mimicking adenocarcinoma morphology. Nuclear pleomorphism showed the strongest positive correlation with nucleolar prominence (r=0.78) and mitotic activity (r=0.67), while cell cohesion demonstrated negative correlations with both nuclear pleomorphism (r=-0.32) and mitotic figures (r=-0.47). Melanin pigment content correlated positively with cytoplasmic volume (r=0.63) but showed only moderate association with nuclear features. Diagnostic concordance between cytological classification and subsequent histopathological confirmation reached 84.6% overall, with epithelioid patterns achieving the highest agreement rate at 94.4% and amelanotic cases showing the lowest at 50.0%. Interobserver agreement between two independent pathologists yielded a kappa coefficient of 0.79, indicating substantial concordance. These findings establish a systematic Cytomorphological framework for canine ocular melanoma classification through FNAC and highlight pattern-specific diagnostic reliability differences that carry practical implications for clinical decision-making. The recognition of balloon cell and signet-ring variants as distinct cytological entities expands the morphological spectrum beyond the traditional epithelioid-spindle dichotomy.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.010 | 0.007 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.002 | 0.001 |
| Bibliometrics | 0.003 | 0.001 |
| Science and technology studies | 0.000 | 0.004 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.002 | 0.002 |
| Research integrity | 0.001 | 0.005 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".