The report, led by Freya Townsend of Wear Referrals Veterinary Hospital in Stockton-on-Tees, United Kingdom, describes three dogs in which metastatic mast cell tumours produced polyostotic vertebral lesions, meaning tumour deposits scattered across multiple vertebrae rather than a single site of bone destruction. According to the authors, only one previous report in the veterinary literature has documented polyostotic mast cell tumour metastasis affecting the vertebrae. That scarcity is precisely what makes the new series noteworthy: it suggests that mast cell tumours deserve a place on the differential diagnosis list for extradural and polyostotic vertebral disease, a consideration that could influence biopsy decisions, staging protocols and prognostic conversations with owners.

The first case involved an eight-year-old neutered male small crossbreed presented originally for a small, raised mass on the upper lip. Histopathology classified it as a grade II tumour under the traditional Patnaik system and low grade under the more prognostically stringent Kiupel system, with a low mitotic count of one mitosis per ten high-power fields. The mass was excised completely, albeit with a narrow deep margin. Seven months later, the right mandibular lymph node was enlarged and biopsy confirmed metastatic mast cell disease. Fine needle aspirates of the opposite lymph node, liver and spleen were reassuringly negative at that stage, and the dog was started on lomustine chemotherapy. When a subcutaneous nodule later appeared at the surgical site and cytology again confirmed metastasis, treatment was switched to toceranib phosphate before referral to a specialist oncology service.

At the referral hospital, computed tomography revealed enlargement of the right mandibular and bilateral medial retropharyngeal lymph nodes, and surgical removal of these nodes confirmed overt metastatic mast cell infiltration, graded HN3 under the Weishaar classification system for nodal mast cell metastasis. The dog then received vinblastine chemotherapy combined with prednisolone, followed by a five-day course of radiotherapy totalling 20 Gy to the surgical site. One week after radiotherapy ended, the dog became reluctant to exercise. Neurological examination revealed pain on palpation of the thoracolumbar region, and within another week the dog had developed a hunched spine and ambulatory paraparesis, with absent postural reactions in the pelvic limbs. Blood work showed elevated C-reactive protein alongside neutropenia, leukopenia and reduced platelets, consistent with both inflammatory disease and chemotherapy side effects.

The second case was a fifteen-year-old neutered female springer spaniel whose story began with removal of a two-centimetre subcutaneous mass from the right caudal mammary gland. That tumour carried a high mitotic count exceeding ten mitoses per ten high-power fields, and the regional lymph node was already invaded by sheets of hyperchromatic, intermediately differentiated mast cells, classified HN2. The mass tested negative for a c-KIT mutation. Seven months after surgery, a new groin mass and imaging findings of enlarged abdominal lymph nodes and liver nodules confirmed widespread metastasis, and vinblastine with prednisolone was initiated. Two months into chemotherapy, the dog developed ambulatory paraparesis that progressed to non-ambulatory paraparesis by the time of specialist assessment, with pain suspected on palpation of the cervical spine and neurological signs localising to the mid-thoracic spinal cord segments.

The third patient, a thirteen-year-old neutered male Nova Scotia Duck Tolling Retriever, had a long history of mast cell tumours, including a recurrent low-grade shoulder mass and, more recently, a twenty-millimetre high-grade Kiupel tumour on the mid back with narrow surgical margins. Abdominal ultrasound had already shown nodular changes in the liver and spleen. The dog completed a twelve-week course of vinblastine and prednisolone but skipped restaging, and seven months later returned with a one-week history of non-ambulatory paraparesis, a large thoracic wall mass in the armpit region, and pain on palpation of the cranial thoracic spine. Neurological deficits again localised to the T3-L3 spinal cord segments, while reduced withdrawal reflex in the right forelimb was attributed to the large mass itself.

Magnetic resonance imaging of the vertebral column in all three dogs revealed the series’ defining finding: multiple lesions across many vertebrae, ranging from well-defined nodules to ill-defined patches, accompanied by similar lesions in the iliac bones of all three dogs and, in some, the ribs, sternebrae and scapula. Technically, every vertebral lesion appeared mildly hyperintense to isointense relative to the spinal cord on both T2-weighted and T1-weighted sequences, hyperintense on short tau inversion recovery sequences, and showed moderate homogeneous enhancement after gadolinium contrast. Vertebral shape was preserved, but cortical osteolysis was present in all cases, and several lesions breached the cortical margins to invade the extradural space and perivertebral soft tissues, compressing the spinal cord from moderately to severely. All three dogs were humanely euthanised following imaging, at the request of their caregivers.

Post-mortem histopathology cemented the diagnosis. In the first two dogs, neoplastic round cells filled the intertrabecular spaces of affected vertebrae, effacing normal haematopoietic tissue and, in the first case, extending into adjacent skeletal muscle and the extradural space, with mitotic counts of 49 and 5 per ten high-power fields respectively. Immunohistochemistry proved decisive: the neoplastic cells stained positive for CD117, a marker of mast cells, with c-KIT staining patterns II and III, while negative CD3 and negative CD20 or CD79A staining excluded both T-cell and B-cell lymphoma. In the third dog, the vertebral body itself showed only inflammatory change, but the extradural mass at T5 displayed a neoplastic round cell population with a mitotic count of 30 per ten high-power fields and confirmatory CD117 positivity. Splenic and hepatic metastasis was confirmed in the first two dogs, underscoring that none of the three had isolated spinal disease.

The imaging signature carries practical weight. In a retrospective study of sixty dogs with vertebral column tumours, preservation of vertebral shape, homogeneous contrast enhancement and lesions centred on bone were features associated with round cell neoplasms, a group that includes mast cell tumours, lymphoma, multiple myeloma, plasma cell tumours and histiocytic sarcoma. The signal intensities reported here, iso- to mildly hyperintense on T1 and T2 weighting, resemble those described for vertebral multiple myeloma and lymphoma, meaning mast cell metastasis can mimic its more familiar round cell cousins. Notably, the authors highlight that their T1 and T2 findings differ from the only prior polyostotic case, in which lesions were T1 hypointense and T2 hyperintense, adding to the recognised variability of mast cell tumour metastases.

What distinguishes this series from earlier reports is the pattern of bone involvement. Previous descriptions of mast cell tumours invading bone have mostly involved local infiltration or lysis near the primary tumour, such as a subcutaneous tumour invading the stifle joint and adjacent tibial plateau, or a disseminated tumour eroding the sphenoid bone and causing blindness. Most reported spinal mast cell tumours have been extradural masses compressing the cord without touching the vertebrae at all. By contrast, the three dogs described here developed distant metastatic deposits as multiple focal lesions in separate vertebrae, a haematogenous spread pattern more reminiscent of carcinoma or multiple myeloma than of the typical mast cell tumour. The authors conclude that metastasis should be actively considered in any dog with a previously diagnosed mast cell tumour that develops spinal pain, and that mast cell disease belongs among the differentials for polyostotic, extradural vertebral lesions, a message that may prompt earlier biopsy and more complete staging in similar patients.

Subject of Research: Metastatic mast cell tumours causing polyostotic vertebral lesions in dogs

Article Title: Metastatic mast cell tumours causing polyostotic vertebral lesions in three dogs

Article References: Metastatic mast cell tumours causing polyostotic vertebral lesions in three dogs. (n.d.). https://doi.org/10.1186/s44356-025-00050-3

Image Credits: AI Generated

DOI: 10.1186/s44356-025-00050-3

Keywords: canine, mast cell tumour, metastasis, vertebral lesions, MRI, histopathology, veterinary oncology, spinal tumour, polyostotic, CD117, round cell tumour, paraparesis

Mast cell tumours are the most frequently diagnosed cutaneous malignancy in dogs, accounting for an estimated 16 to 21 percent of all skin neoplasms. They arise from mast cells, immune cells rich in inflammatory mediators such as histamine and heparin, and typically present as masses in the skin or the tissue beneath it. Their biological behaviour spans an extraordinary range: some are cured permanently by simple surgical excision, while others ulcerate, recur locally and spread to lymph nodes, liver and spleen. Paraneoplastic effects driven by the release of mast cell granules can produce itching, bruising, skin swelling and gastrointestinal signs, complicating the clinical picture. Two histological grading systems, the three-tier Patnaik scheme and the two-tier Kiupel scheme, are widely used to predict behaviour, and both have been shown to be consistently prognostic, particularly when applied together.

Golden Retrievers have repeatedly been identified as a breed at increased risk of MCTs, and germline genetic studies have pinpointed risk variants in genes including GNAI2 and a hyaluronidase gene in US Golden Retrievers. Yet until now, no epidemiological study had specifically characterised MCT frequency, clinical features and survival within the breed in the United States. The GRLS, a prospective cohort of 3,044 Golden Retrievers enrolled between June 2012 and April 2015 and balanced by sex across five geographic regions, offered a uniquely powerful opportunity. Dogs were followed annually with owner and veterinarian questionnaires, biological samples and a dedicated biopsy submission pathway, with histopathology reviewed by two blinded veterinary pathologists. The study’s primary cancer endpoints include haemangiosarcoma, lymphoma, osteosarcoma and high-grade MCT, with high grade defined as Patnaik grade 3 or Kiupel high.

The headline numbers are striking. Of the 3,044 dogs, 164, or 5.39 percent, were diagnosed with a total of 234 mast cell tumours, yielding an incidence rate of 5.58 per 1,000 dog years at risk. A lifetable analysis revealed that young dogs were rarely affected: 99.1 percent of the cohort reached five years of age without an MCT diagnosis. Annual incidence risk peaked at 1.39 percent in dogs aged greater than eight to nine years, before declining in the oldest age groups. The authors note that this decline mirrors patterns seen in other veterinary and even human cancers, where incidence falls in extreme old age, possibly reflecting cellular senescence, stem cell exhaustion or a cancer-resistant phenotype, though diagnostic bias in geriatric patients may also contribute.

Compared with incidence figures from a mixed-breed insured population in Sweden, the Golden Retriever rate appears up to tenfold higher, which the researchers interpret as evidence of a genuine and substantial breed predisposition rather than an artefact of geography or study design. The practical message for owners is clear: vigilance for skin masses, particularly as dogs enter middle and older age, is warranted, and any new lump should prompt veterinary investigation rather than a wait-and-see approach. The median age at first diagnosis in the cohort was just over eight years.

The tumours themselves were predominantly low grade. Cutaneous tumours accounted for 70.5 percent of events and subcutaneous tumours for 16.7 percent, with the remainder being metastatic entries, mucosal or visceral primaries, or digital masses. The most common anatomical locations were the torso, limbs and head and neck, consistent with distributions reported in multi-breed populations. Histopathological grading was available for nearly all cutaneous tumours, and the most frequent grade was the intermediate-low P2KL category. Overall, only 47 of the 234 tumours, or 20.1 percent, met the study’s high-grade definition, a proportion consistent with previous reports of 22 to 26 percent high-grade disease in broader populations. Notably, the findings do not support earlier suggestions that Golden Retrievers are disproportionately prone to high-grade tumours.

Recurrence and spread were comparatively uncommon. Most dogs, 84.2 percent, had a solitary tumour, while 15.9 percent developed new de novo masses at distinct sites, with a median interval of 368 days between the first and subsequent tumours. Local recurrence occurred in just under five percent of cases, and documented metastasis in 9.8 percent, most often to lymph nodes. Critically, every dog with metastatic disease had at least one high-grade tumour; no dog with only low-grade MCTs was found to have spread. The authors suggest this could influence clinical staging recommendations, since extensive staging appears to have low diagnostic yield in low-risk patients, although the absence of standardised staging protocols means some metastases may have gone undetected.

The survival analysis produced the study’s most reassuring result. Median lifespan was 11.68 years in dogs diagnosed with MCT and 11.75 years in the remaining cohort, a difference that was not statistically significant. Median survival time from first MCT diagnosis to death from any cause was 1,367 days, and only 19 dogs, or 11.6 percent, had MCT recorded as their cause of death. Overall survival probabilities after diagnosis were 81.7 percent at one year, 70.0 percent at two years and 40.6 percent at five years. When the analysis was stratified, however, the prognostic weight of tumour biology became evident: the presence of metastasis, a high histological grade, or local recurrence were each associated with statistically significantly reduced survival, while the development of additional de novo tumours was not. Nearly 90 percent of the dogs that died from their disease had at least one high-grade tumour.

The researchers acknowledge several limitations. Cohort recruitment relied on word-of-mouth and snowball sampling, dogs were required to have three-generation pedigrees, and participating owners were highly engaged, with subsidised histopathology likely boosting diagnostic rates relative to the wider population. Treatment details were largely unavailable, precluding analysis of therapeutic impact, and the number of MCT-related deaths was too small for multivariable modelling. Nevertheless, the study’s general-practice setting gives it a realism that insurance-claim and referral-based studies lack. Its overall message is one of measured optimism: for most Golden Retrievers, a mast cell tumour diagnosis is not life-limiting, low-grade disease carries an excellent prognosis with prompt and appropriate management, and the findings justify early investigation and treatment of skin masses rather than fatalism. As the GRLS cohort continues to yield data, it is cementing its role as one of the most valuable resources in comparative oncology, with implications that may ultimately extend to human mast cell disorders and cancer research more broadly.

Subject of Research: Epidemiology, clinical features and survival of mast cell tumours in Golden Retrievers enrolled in the Golden Retriever Lifetime Study

Article Title: Mast cell tumours in the Golden Retriever Lifetime Study: a cohort study assessing frequency, clinical features and survival

Article References: Stratton, Z. V., Brodbelt, D. C., Guillén, A., O’Neill, D. G., Labadie, J., Swafford, B., & Taylor, C. (2026). Mast cell tumours in the Golden Retriever Lifetime Study: a cohort study assessing frequency, clinical features and survival. Veterinary Oncology, 3(1), Article 10. https://doi.org/10.1186/s44356-026-00060-9

Image Credits: AI Generated

DOI: 10.1186/s44356-026-00060-9

Keywords: Golden Retriever, mast cell tumour, canine cancer, veterinary oncology, Golden Retriever Lifetime Study, dog lifespan, histological grading, Kiupel, Patnaik, metastasis, incidence, survival analysis