Canine appendicular osteosarcoma substantially increases the risk of pathological fractures. Limb-sparing approaches such as Stereotactic Body Radiation Therapy (SBRT) can extend and improve the quality of life in large-breed dogs; however, recent clinical studies have reported high post-SBRT fracture rates and significant complications following prophylactic stabilization. While patient-specific Finite Element Analysis (FEA) can estimate pre- and post-stabilization fracture-initiation thresholds, its computational burden limits its clinical applicability. This study presents Machine Learning (ML) surrogates to rapidly predict implant performance using data derived from high-fidelity FEA simulations. These simulations employed physics-faithful bone models with heterogeneous elasto-plastic material properties reconstructed from Computed Tomography (CT) scans of 16 dogs. The eXtended Finite Element Method (XFEM) was employed to capture crack initiation and propagation under 25 distinct loading scenarios, both with and without medullary conformal stabilization. Five ML models, including MLP, SVR, RF, XGBoost, and HistGBR were trained and evaluated using biological and morphometric features such as body weight, lesion location, bone length as well as 825 FEA simulation-derived crack-initiation loads. Hyperparameters were optimized via Bayesian tuning, and simulation-level stability was assessed across training-testing splits ranging from 50:50 to 90:10, while patient-level generalization was evaluated separately using nested Leave-One-Group-Out (LOGO) cross-validation. XGBoost demonstrated the best predictive performance on 165 held-out cases, achieving an average R2≈0.90 and a normalized mean absolute error of approximately 8%. Patient-level performance was more consistent for humeral cases than tibial and radial cases, emphasizing the need for larger, bone-type-balanced datasets. Feature-importance analysis revealed lesion burden and body weight as dominant predictors, with anatomical scaling parameters (e.g., bone length, diaphyseal thickness) and density proxies contributing secondary effects, while sex and age showed negligible contributions within the current cohort. Retrospective clinical outcomes from six treated dogs were examined descriptively and provided preliminary clinical context rather than formal validation. FEA and surrogate predictions suggest that delayed fracture-initiation can be achieved through intramedullary implant stabilization, although its effectiveness varies among patients. The proposed proof-of-concept framework provides a scalable, data-driven foundation for clinical decision support, with predictive accuracy expected to improve as additional outcome data become available.

Oral fibrosarcoma is a highly invasive tumour with local recurrence rates of up to 57.9% following surgical excision. The optimal surgical margins for long-term local control of oral fibrosarcoma have not been ascertained, especially when tumour invasion into the mandibular canal is present. The objective of this study was to evaluate the recurrence of mandibular fibrosarcoma in dogs following mandibulectomy procedures based on the presence or absence of mandibular canal invasion. Medical records of dogs that underwent a mandibulectomy for fibrosarcoma between January 2005 and December 2023 at 9 veterinary referral centers were reviewed. The size of the tumour, surgical procedure performed, surgical margins obtained, and long-term outcome were recorded. Fisher's exact and Mann-Whitney U tests were used to compare the association between different factors with development of local recurrence. Forty-nine dogs were included. Surgeries performed included segmental mandibulectomy (n = 14), unilateral mandibulectomy (n = 11), bilateral rostral mandibulectomy (n = 9), unilateral rostral mandibulectomy (n = 5), and three-quarter (¾) mandibulectomy (n = 3). Forty dogs had complete histologic margins. Mandibular canal invasion was reported in 14 dogs. Follow-up was available for a median of 493 days postoperatively. Eight dogs were diagnosed with local recurrence. Five dogs with local recurrence had mandibular canal invasion at the initial surgery. No variables evaluated individually were significantly associated with local recurrence. Multivariable logistic regression found the absence of mandibular canal invasion was associated with reduced odds of recurrence (odds ratio, 0.06; 95% confidence interval 0.004-0.835; p = 0.036) when adjusted for the type of mandibulectomy performed and the histopathologic margin status. Further research is needed to determine the optimal surgical margins for dogs with mandibular fibrosarcoma.

The cardiac-gated computed tomography (CT) scan reports of 12 dogs with right auricular appendage masses between 2018 and 2023 were reviewed to describe the use of cardiac-gated CT for assessment of right auricular appendage tumour location and extent and for staging. Imaging reports from thoracic radiographs, CT scans, abdominal ultrasound, and echocardiogram were evaluated for detection of a cardiac mass, mass location on the heart, and detection and location of suspected metastases. Surgery and necropsy reports were evaluated for definitive location of the cardiac mass. Descriptive statistics were performed. Cardiac-gated CT identified a mass that was confined to the right auricular appendage in seven dogs and involved additional cardiac structures in five dogs. Metastases were suspected on CT in 10 dogs. Surgery with the intent to remove the mass for cytoreduction was pursued in five dogs. Right auriculectomy was performed in four dogs. One dog whose mass was suspected to extend beyond the right auricular appendage on CT died during attempted surgical resection. Cardiac-gated CT helped guide clinical decision making by providing information about the location and extent of the mass to assess feasibility of surgical resection and also functioned as a sensitive staging test.

Case summary A 6-year-old, neutered male domestic shorthair cat was referred for evaluation of a recurrent subcutaneous mass on the right caudodorsolateral hip, 4 months after excision of a presumed feline injection site sarcoma (FISS). Advanced imaging revealed a bilobed soft tissue mass closely associated with the sciatic nerve and rectum. Surgical excision was limited by adjacent structures, and histopathology confirmed a sarcoma with incomplete margins. Definitive-intent radiation therapy was administered postoperatively. Follow-up imaging initially demonstrated no evidence of local recurrence. Approximately 9 months after completion of radiation therapy, the cat developed progressive pelvic limb paraparesis, fecal incontinence and urinary retention. MRI identified a large contrast-enhancing extradural spinal lesion extending from L5 to the sacrum, with suspected intramedullary invasion and marked thickening of the lumbosacral nerve roots. Surgical exploration with hemilaminectomy and spinal cord biopsy revealed a poorly differentiated sarcoma histologically similar to the original tumor. Progressive disease was confirmed on follow-up imaging, and palliative radiation therapy was administered. Despite treatment, the cat developed severe neurologic deterioration and was humanely euthanized. Relevance and novel information This report describes the first documented case of spinal cord invasion secondary to a FISS-like fibrosarcoma without local recurrence at the primary site. Perineural invasion along the sciatic nerve is proposed as a biologically plausible mechanism of tumor extension. This case highlights an uncommon but severe pattern of disease progression and underscores the importance of considering perineural spread in incompletely excised FISS-like tumors associated with major peripheral nerves.

Objective:To describe outcomes in cats with primary appendicular bone tumors treated with complete or partial amputation, with or without adjuvant chemotherapy. Methods:This retrospective study analyzed cats with histologically confirmed primary appendicular bone tumors treated surgically between 2008 and 2019. Data included signalment, clinical signs, tumor location, preoperative imaging, amputation level, adjunctive therapy, histologic characteristics, and oncologic outcomes. Results:76 cats were included, with osteosarcoma being the most commonly diagnosed tumor. Median survival time (MST) for cats with osteosarcoma was 469 days, with 1- and 2-year survival rates of 56.8% and 40.4%, respectively. The MST for cats with chondrosarcoma was 1,302 days, with 1- and 2-year survival rates of 91.7% and 66.7%. Overall metastatic rate was 32.9%, and 36.2% for osteosarcoma specifically; scapular tumors had the highest metastatic rate (87.5%). Preoperative pulmonary metastasis significantly shortened MST in cats with osteosarcoma (152 vs 573 days). In cats with osteosarcoma without preoperative pulmonary metastasis, adjuvant chemotherapy significantly improved MST (1,466 vs 440 days). Negative prognostic indicators for cats with osteosarcoma were increased age and presence of suspected metastasis at any time. Conclusions:Appendicular osteosarcoma in cats had a good prognosis following amputation alone, despite a higher metastatic rate than previously reported; however, adjuvant chemotherapy significantly improved survival time in cats with nonmetastatic osteosarcoma. Appendicular chondrosarcoma had an excellent prognosis following definitive surgery alone. Clinical Relevance:Cats with nonmetastatic osteosarcoma at diagnosis should be treated with both definitive surgery and adjuvant chemotherapy.

An 11-year-old, female, spayed, mixed breed dog was presented with a 1-month history of oral pain. No major physical abnormalities were reported. A comprehensive oral examination was recommended. At intubation, temporomandibular joint crepitus and decreased range of motion were observed. Three teeth were surgically extracted following the diagnosis of advanced external resorption. Four months later, the dog was reassessed for persistent oral pain. Right-sided dorsomedial periocular and nasal bone swelling, obscured by long facial hair, was appreciated. Computed tomography revealed a large right caudal sinonasal mass with extensive bony lysis. Palliative care was elected following a presumptive diagnosis of neoplasia. Cytology of the nasal mass was most consistent with squamous cell carcinoma. This advanced case of sinonasal squamous cell carcinoma with an atypical clinical presentation and subtle physical exam findings highlights the importance of performing a thorough physical examination and considering all identified abnormalities while refining a diagnosis.

Osteosarcoma is the most common primary bone tumour in dogs, with approximately 75% of cases occurring in the appendicular skeleton. Standard-of-care therapy consists of limb amputation followed by carboplatin chemotherapy. A minority of dogs have limb-sparing treatments including stereotactic body radiation therapy (SBRT) or surgery. SBRT has a high incidence of pathologic fracture (41%-80% of cases) following treatment, which often results in amputation or euthanasia. Prophylactic bone stabilisation following SBRT has not been recommended due to high complication rates. The IlluminOss system (IS) is an intramedullary implant consisting of a light-curable polymer within an inflatable balloon catheter, which is approved in humans for traumatic fractures and prevention of fractures secondary to bone metastases. We performed a study to assess the safety and feasibility of using the IS following SBRT in six dogs with suspected appendicular osteosarcoma. The IS was placed the day after completion of SBRT. Five of six dogs received adjuvant carboplatin chemotherapy. The IS was well tolerated with no implant-associated infections or immediate post-operative complications occurring. Pathologic fractures occurred in four dogs with a median fracture-free interval of 107 days. Three dogs ultimately underwent amputation due to pathologic fractures. No other post-operative complications occurred. The median survival time was 156 days. These findings suggest that the IS may be a palliative option for dogs following SBRT, but further research to optimise use in the dog and evaluation of the use of the IS with ancillary fixation is necessary.

A 7-year-old female, spayed, domestic shorthair presented with a 24-hour history of anorexia, lethargy and melaena. The cat was hospitalized and received treatment for hypovolemia, various electrolyte abnormalities and severe anaemia with a blood transfusion, intravenous fluids and medications. Abdominal ultrasound identified a pyloroduodenal nodule. Additional advanced diagnostics were not pur due to persistent intestinal haemorrhage and recurring critical status necessitating multiple blood transfusions. Surgical exploration identified a mass within the proximal duodenal lumen orad to the major duodenal papilla. The affected segment of duodenum and pylorus was resected, preserving the common bile duct, and a duodenogastric anastomosis was performed. Following surgery, the cat remained haemodynamically stable, and 5 days post-operatively, all other clinical signs and electrolyte abnormalities resolved. Histopathological assessment of the mass was consistent with an intestinal adenoma. Six months post-operatively, the cat was reported to have fully recovered without recurrence of clinical signs.

Handheld confocal laser endomicroscopy (CLE) enables an instantaneous assessment of the cellular morphology of different tumor types and margin assessment ex vivo. Here, we describe the correlation between CLE images and histology and the feasibility of incorporating this technology in assessing surgical biopsy specimens. A CLE microscope (Optiscan, ViewnVivo) acquired high-definition confocal images of surgical biopsy cases and a single autopsy case (15 canine, 1 feline, and 1 equine cases). Following minimal training on the imaging modality, 14 participants (6 anatomic pathologists and 8 anatomic pathology residents) were asked to assess 17 cases with and without signalment and clinical history. The CLE captured detailed cellular morphology and tissue microarchitecture in various surgical biopsy and select autopsy specimens. Averaging the diagnostic accuracy with and without clinical history, study participants were able to distinguish abnormal tissue in 15/17 cases, neoplasia from inflammation in 12/17 cases, and the cellular morphology of neoplasia in 8/13 cases. Across all questionnaires, there was a statistically significant improvement in the diagnostic accuracy when clinical history was provided (P-value: 3.07E-07 to .005, paired t-test). CLE enables the capture of the high-resolution microarchitecture of tissue and can be readily correlated to histology images. We demonstrated that with little training, anatomic pathologists could evaluate surgical biopsy specimens that can provide a rapid preliminary diagnosis and margin assessment.

A 6‐year‐old, neutered, male German shepherd dog presented to the Emergency and Critical Care Service at the Ohio State University Veterinary Medical Center with bilateral pleural effusion. Thoracic computed tomography, among other diagnostics, failed to identify the cause of the pleural effusion. After approximately 8 months of management with therapeutic thoracocentesis to alleviate clinical signs, empirical treatments and regular monitoring, a primary rib lesion was identified on repeat thoracic computed tomography. A rib resection was performed to remove the lesion and obtain pleural biopsy samples. Diffuse nodular to coalescing changes along the pleural surface were identified intraoperatively. Histopathology of the rib lesion provided a diagnosis of soft tissue sarcoma, and the pleural samples confirmed sarcomatosis. The dog received two doses of intracavitary carboplatin following surgery. Despite treatment, the dog was euthanased shortly after the second dose, 10 months after initial presentation to the Ohio State University Veterinary Medical Center. This case emphasises the importance of considering repeated diagnostic imaging tests when managing cases of recurrent pleural effusion without a definitive diagnosis. This case also emphasises the importance of including sarcomatosis as a differential diagnosis for pleural effusion in dogs.

Canine oral malignant melanoma (OMM) has a high potential for lymph node (LN) metastasis. Standard care involves surgical excision of the OMM with sentinel and draining LNs regardless of metastatic status but carries the risk of complications. Optical coherence tomography (OCT) is a rapid, noninvasive imaging modality that has been evaluated for LN metastasis detection in human breast cancer but not yet translated to canines. The purpose of this study was to (1) compare OCT imaging features from nonmetastatic and metastatic LNs with corresponding histopathology and (2) evaluate the diagnostic accuracy of OCT imaging in identifying metastatic LNs. Thirteen dogs with OMM were prospectively enrolled and sentinel LNs were identified by indirect computed tomography lymphography. OMM and draining LNs were surgically removed. Excised LNs (n = 50) from thirteen dogs were imaged with OCT and submitted for histopathology. OCT images of 18 LNs from the first five enrolled dogs were compared to histopathology to identify image features of metastatic and nonmetastatic LNs and identify images for observer training. The subsequent OCT images of 32 LNs of eight dogs were used to generate a test set for six observers with varying OCT experience for assessment of diagnostic accuracy. The sensitivity, specificity, and correct classification rate of OCT imaging for OMM LN metastasis in dogs was 75% (95% CI: 61.2%-85.1%), 76.6% (95% CI: 70.1%-82.0%), and 76.3% (95% CI: 70.5%-81.2%), respectively. OCT image features of nonmetastatic and metastatic LNs show diagnostic potential for intraoperative detection of OMM LN metastasis.

Intraoperative surgical margin evaluation is not routine in veterinary medicine. Polarisation-sensitive optical coherence tomography (PS-OCT) is a variant of spectral domain optical coherence tomography (SD-OCT) that can provide real-time cross-sectional imaging of surgical margins with additional information about the polarisation of light in tissues. The aims of this study were (1) to compare PS-OCT surgical margin images to histopathology of excised canine skin and subcutaneous tumour specimens, and (2) to determine if the addition of PS-OCT images improved the diagnostic accuracy of surgical margin assessment. The authors hypothesised that PS-OCT image features would resemble histopathologic tissue features and the addition of PS-OCT images would improve the accuracy of margin assessment. Sixty-one dogs with 79 skin and subcutaneous tumours were prospectively enrolled. Tumours were excised, the surgical margins were imaged with OCT and then submitted for histopathology. Six masked readers first received image interpretation training in SD-OCT only, followed by training in combined SD-OCT and PS-OCT 1 week later. The readers interpreted each image or video for the presence of cancer and the results were compared to histopathology. PS-OCT imaging features of surgical margin tissues were consistent with tissue histopathologic features at low power. The overall reader median sensitivity and specificity were 90.9% and 95.6% for SD-OCT only and 90.9% and 91.3% for combined SD-OCT and PS-OCT. The addition of PS-OCT images did not improve the diagnostic accuracy of the surgical margin assessment for skin and subcutaneous tumours but resulted in high accuracy of margin interpretation with readers of varying experience.

Objective:To evaluate the recovery outcomes of cats following limb amputation for appendicular bone tumors. Methods:This retrospective, multi-institutional study included cats that underwent thoracic or pelvic limb amputation to treat primary appendicular bone tumors (2006 to 2019). Short- and long-term postoperative complications were investigated. Owners were surveyed to evaluate their perceptions and satisfaction regarding postoperative adaptation and recovery outcomes. Fisher exact tests were used to compare the results between different levels of amputation performed. Results:A total of 68 client-owned cats were included. Mild short-term (≤ 14 days) and long-term (> 14 days) postoperative complications were reported in 5 (7.4%) and 3 (4.4%) cats, respectively. Overall, time to return to walking without support was < 3 days in 69.7% of cats and 3 to 7 days in 16.7%. Activity level changes were reported as no change in 75.8% of cats. There were no behavioral changes in 92.3% of cats. Quality of life following amputation was recorded as excellent in 82.4% of cats. Owner satisfaction was reported as very satisfied, moderately satisfied, or satisfied in 98.5% of cats. There was no significant difference between thoracic limb and pelvic limb amputation in owner satisfaction or postoperative complications (short-term, OR = 0.39 [95% CI, 0.035 to 2.39]; long-term, OR = 0.41 [95% CI, 0.0074 to 5.39]). Conclusions:Most cats showed prompt and complete recovery following thoracic or pelvic limb amputation, with a high level of owner satisfaction and low incidence of postoperative complications. Clinical Relevance:Thoracic or pelvic limb amputation in cats can result in excellent recovery outcomes.

Cross-sectional imaging may be used to characterise the location and extent of colorectal mesenchymal tumours (CRMTs). Given the anticipated variation in tumour behaviour and varying morbidity based on surgical margins, a reliable, non-invasive means of predicting malignant potential could facilitate case management. The purpose of this multi-institutional, retrospective study was to determine the diagnostic accuracy of contrast-enhanced CT for distinguishing benign and malignant CRMTs. Twenty-seven dogs with CRMTs were included. Initial diagnoses were reviewed, and slides or blocks were available for 24/27 dogs for further histologic review and immunohistochemical labelling for smooth muscle actin, KIT and vimentin. Two masked radiologists reviewed DICOM images for tumour characteristics, including a final, binary, consensus, subjective interpretation of malignancy. Eighteen tumours (66.7%) were classified as leiomyoma, one (3.7%) as a benign other non-lymphogenic intestinal mesenchymal tumour (benign), one (3.7%) as leiomyosarcoma, and seven (25.9%) as gastrointestinal stromal tumour (malignant). Agreement between radiologists ranged from none to weak for categorical variables, with no agreement (κ = 0.135) for the final assessment of a tumour as benign or malignant. Substantial overlap was noted between groups, with no single categorical variable demonstrating high accuracy as a predictor of malignancy. Consensus final assessment was a sensitive (80.0%) but not specific (29.4%) predictor of malignancy (accuracy: 48.2%). No association was identified between CT determination of malignancy and histologic determination of malignancy (p = 0.678). Non-standardised contrast-enhanced CT was ineffective at distinguishing malignant from benign CRMTs in this study.

Background Surgical margin status can affect the risk for recurrence in dogs with cutaneous and subcutaneous masses. Histopathology is the current gold standard for margin assessment, despite evaluating small amounts of the surgical margin. Optical coherence tomography (OCT) has been described for surgical margin assessment following the excision of canine cutaneous and subcutaneous tumors. Objective To assess the rates of recurrence and metastasis following excision with an incomplete margin on OCT and confirmed with histopathology. Animals and procedure Seventy-one excised canine cutaneous and subcutaneous tumors underwent OCT imaging and histopathologic assessment. Results Of 61 tumors, 51 were malignant, including 21 soft tissue sarcomas and 21 mast cell tumors. Ten dogs experienced local tumor recurrence, with 7/10 and 8/10 having incomplete margins on OCT and histopathology, respectively. Ten dogs experienced distant metastasis, with 6/10 and 8/10 having incomplete margins on OCT and histopathology, respectively. Conclusion and clinical relevance Local recurrence occurred in tumors with predominately incomplete margins following advanced surgical margin assessment; however, not all tumors with incomplete margins developed local recurrence. Further prospective research is needed to assess the effect of entire surgical margin imaging on patient outcomes.

Soft tissue sarcomas (STS) are malignant, locally invasive neoplasms arising from mesenchymal cells. Optical coherence tomography (OCT) has been shown to identify tissue types and can be used for margin assessment during STS removal surgeries. Due to the large number of images produced, automatic algorithms are worthwhile to screen OCT images effectively. In this paper, we report a method based on deep learning for fast and accurate intra-operative assessment of OCT images with polarization-sensitive (PS-OCT) enhancement. Based on the predictive model, we designed a method to localize cancerous areas based on a cancer probability diagnosis curve. We tested our proposed method on a canine STS surgical margin image dataset, and the result showed 0.989 Area Under the Receiver Operating Curve (AUROC) and 91

BACKGROUND:The utility of cytologic evaluation to distinguish adrenocortical tumors and pheochromocytomas in dogs has not been thoroughly investigated, partly because of the perceived risks of the procedure. OBJECTIVES:Report test characteristics of fine needle aspiration (FNA) and cytologic evaluation for differentiation of adrenocortical tumors and pheochromocytomas in dogs. Complications associated with FNA also were recorded. ANIMALS:Thirty-eight dogs with 40 adrenal tumors that had FNA and cytologic evaluation performed before adrenalectomy were included in the study from three institutions. Tumors included 17 pheochromocytomas, 21 adrenocortical tumors, 1 concurrent adrenocortical adenoma and pheochromocytoma, and 1 malignant neoplasm. RESULTS:Of the 40 FNA cytologic aspirations performed, 35 (87.5%) had a predominant cell type identified and therefore were considered of diagnostic quality. Of these, 30 (85.7%) correlated with the final histopathological diagnosis. When all samples were included, FNA and cytologic evaluation had a sensitivity of 77.3%, specificity of 76.5%, positive predictive value of 81.0%, negative predictive value of 72.2%, and accuracy of 76.9% for identifying adrenocortical tumors. For pheochromocytomas, these values were 72.2%, 95.2%, 92.8%, 80.0%, and 84.5%, respectively. Six (15.9%) dogs had self-limiting complications associated with the FNA procedure. CONCLUSION AND CLINICAL IMPORTANCE:Fine needle aspiration and cytologic evaluation of adrenal tumors has a low complication rate and can help differentiate adrenocortical tumors and pheochromocytomas. Thus, cytologic evaluation of adrenal tumors should be considered to help differentiate adrenal tumors and allow more individualized treatment of affected dogs.

A 10-year-old, male, neutered labrador retriever was diagnosed with a left-sided anal sac adenocarcinoma. At diagnosis, staging with an abdominal computed tomography revealed no intraabdominal lymph node enlargement. Thoracic radiographs revealed a soft tissue pulmonary nodule with cytology consistent with a carcinoma. The dog underwent a left anal sacculectomy, and re-presented 24 days later for a lung lobectomy in which histopathology represented primary anal sac adenocarcinoma metastasis. Forty-nine days after initial presentation, the dog was referred for a right distal radial lytic lesion in which cytology was concerning for osteosarcoma. After 132 days of initial presentation, an abdominal ultrasound revealed normal-sized iliosacral lymph nodes. The dog was humanely euthanased 446 days after initial diagnosis. This case report describes a dog who had a solitary metastatic pulmonary nodule from apocrine gland anal sac adenocarcinoma at the time of presentation with no nodal metastasis identified, which is atypical compared to previous reports.

The treatment of choice for canine alimentary tract neoplasms is surgical excision, but it can sometimes be difficult to achieve wide margins due to neoplasm location, size, or distribution. Optical coherence tomography (OCT) is a rapid, noninvasive imaging modality that uses light to characterise tissue microstructure to allow identification of different tissue types. Spectral domain (SD)-OCT allows for differentiation based on the total light intensity reflected from the tissue. Polarisation sensitive (PS)-OCT detects the polarisation state of light reflected by the tissues. The polarisation properties are phase retardation, degree of polarisation uniformity (DOPU), and optical axis. Our objective was to qualitatively characterise different tissues at the excision sites of alimentary tract neoplasms using OCT. Oral, liver, and other alimentary tumours including stomach, intestine, and pancreas were imaged. Samples were then fixed in formalin, paraffin embedded and stained with haematoxylin and eosin. OCT images and histology slides were compared, and the tissues were qualitatively described by a single investigator. We hypothesized that PS-OCT imaging would provide distinguishing characteristics of tissue appearances that could be used in the future to train observers or artificial intelligence to identify incomplete margins. Our results showed that alimentary tract tumours have disorganised microstructures on SD-OCT and PS-OCT DOPU, and PS-OCT phase retardation and optical axis values that differ from normal tissues. Thus, these characteristics can be used to differentiate neoplastic and normal tissues at surgical margins.

Mucosal melanoma is a rare melanoma subtype associated with a poor prognosis and limited existing therapeutic interventions, in part due to a lack of actionable targets and translational animal models for preclinical trials. Comprehensive data on this tumour type are scarce, and existing data often overlooks the importance of the anatomical site of origin. We evaluated human and canine oronasal mucosal melanoma (OMM) to determine whether the common canine disease could inform the rare human equivalent. Using a human and canine primary OMM cohort of treatment-naive archival tissue, alongside clinicopathological data, we obtained transcriptomic, immunohistochemical, and microbiome data from both species. We defined the transcriptomic landscape in both species and linked our findings to immunohistochemical, microbiome, and clinical data. Human and dog OMM stratified into two distinctive transcriptional groups, which we defined using a species-independent 41-gene signature. These two subgroups are termed CTLA4-high and MET-high and indicate actionable targets for OMM patients. To guide clinical decision-making, we developed immunohistochemical diagnostic tools that distinguish between transcriptomic subgroups. We found that OMM had conserved transcriptomic subtypes and biological similarity between human and canine OMM, with significant implications for patient classification, treatment, and clinical trial design. (c) 2025 The Author(s). The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.