This study evaluated diagnostic trends and the overall utility of cytology in feline patients through the analysis of a large, multicentric dataset from Portugal. A retrospective review of 3068 cytological cases from 130 veterinary practices was conducted, with samples categorised by anatomical location and lesion type. Diagnostic outcomes were statistically assessed, revealing an overall success rate of 66.20%. The highest diagnostic yields occurred in fluid samples (83.48%), glandular tissues (76.67%), and mucous membranes (75.81%), followed by organ-based samples (67.79%), miscellaneous tissues (66.98%), cutaneous/subcutaneous nodules (62.16%), and lymph nodes (57.93%). Neoplastic lesions showed age-associated prevalence, being more common in older cats, with epithelial and melanocytic lesions more frequent in females and round cell/mesenchymal lesions predominating in males. Non-diagnostic samples (33.80%) primarily resulted from insufficient cellularity or suboptimal quality, though no significant correlation existed between diagnostic success and clinical setting. This study underscores that cytology remains a fundamental diagnostic tool in feline medicine, particularly when combined with proper sampling techniques and complementary diagnostic methods, and reinforces its value in clinical decision-making, thereby supporting its broader utilisation in routine veterinary practice.

Background and Aim: Cytology is a minimally invasive, rapid, and cost-effective diagnostic tool widely used in veterinary medicine for evaluating a broad range of lesions. While extensively applied in clinical practice, large-scale epidemiological analyses of cytologic findings in canine populations are limited. This study aimed to evaluate the diagnostic performance of cytology in dogs in Portugal, assessing associations between lesion type, anatomical location, and demographic factors, and to identify patterns that can improve diagnostic utility in veterinary practice. Materials and Methods: A retrospective analysis was conducted on 12,671 cytological samples collected from canine patients between January 2010 and December 2016, submitted by 355 veterinary practices across mainland Portugal. Samples were categorized by anatomical location and diagnostic classification (neoplastic, inflammatory, non-neoplastic/non-inflammatory, and other). Demographic variables (sex, age, and breed) were recorded. Statistical analyses included non-parametric tests, logistic regression, and trend analyses to explore associations between diagnostic outcomes and study variables. Results: The overall diagnostic yield was 69.03%, with the highest rates in fluid (80.21%), mucosal (77.08%), and glandular (75.78%) samples. Cutaneous/subcutaneous lesions, although the most frequent, had the lowest diagnostic yield (66.12%). Of diagnostic cases, 43.94% were neoplastic, with prevalence increasing significantly with age, from 17.75% in dogs ≤1 year to 54.75% in those >10–15 years (p < 0.001). Females were more likely to present epithelial and mesenchymal lesions, while males more frequently had round cell and melanocytic lesions. Breed analysis revealed no significant predispositions after statistical adjustment. Veterinary hospitals achieved higher diagnostic rates than clinics (p = 0.002). Non-diagnostic samples (30.97%) were primarily attributed to poor sample quality or insufficient cellularity. Conclusion: Cytology is a valuable first-line diagnostic modality in canine veterinary practice, particularly effective for fluid, mucosal, and glandular lesions. Lesion prevalence varies significantly with age and sex, highlighting the need for tailored diag­nostic considerations. Standardizing sample collection and preparation techniques, especially for anatomical sites with lower yields, could further improve diagnostic accuracy. While the absence of histopathological confirmation limits definitive clas­sification, the large dataset and standardized diagnostic review strengthen the reliability of findings. Integrating cytology into routine diagnostics can enhance early disease detection, guide treatment decisions, and support epidemiological surveillance. Keywords: canine cytology, diagnostic yield, epidemiology, neoplasia, retrospective study, veterinary diagnostics.

Histological classification of mammary proliferative lesions in dogs and cats is essential for prognostic and predictive studies, as well as for comparative oncology; however, standardization of diagnoses is highly affected by substantial interobserver variability. In this study, a structured diagnostic algorithm based on the Davis–Thompson Foundation classification was assessed for the ability to improve interobserver agreement in the morphological diagnoses of mammary gland lesions in dogs and cats. Consensus diagnoses of 114 selected mammary lesions (91 canine, 23 feline) made by 16 veterinary pathologists with mammary tumor expertise were used as the gold standard, and 79 veterinary pathologists from 21 countries evaluated digitized whole slides in 2 rounds: a first reading without the algorithm and a second reading with the algorithm. Interobserver concordance was measured using unweighted kappa statistics for lesion category (hyperplastic/dysplastic, benign, malignant) and histological subtype. Across all lesions, agreement was higher for lesion category than for histological subtype. A slight improvement in concordance was observed when applying the algorithm, both for category (k = 0.72, before, and k = 0.73, after) and histotype classifications (k = 0.40, before to k = 0.42, after). Also, by using the algorithm, 73/79 raters (92%) modified at least 1 diagnosis and, among these, approximately two-thirds reached agreement with the gold standard in at least 1 case. Considering histotypes, malignant tumors with mixed epithelial and myoepithelial components showed persistently low agreement. Overall, the algorithm provided a reproducible diagnostic framework that may support training and improve standardization of canine and feline mammary tumor classification.