OBJECTIVE To compare percentages of mast cells in lymph node (LN) aspirate samples from clinically normal dogs, dogs with allergic dermatologic disease (ADD), and dogs with cutaneous mast cell tumors (MCTs). DESIGN Prospective cross-sectional study. ANIMALS 20 healthy dogs (group 1), 20 dogs with ADD (group 2), and 20 dogs with an MCT on the head or limbs (group 3). PROCEDURES LN aspirate samples were obtained from easily accessible LNs in group 1, affected skin regions in group 2, and the likely draining LN or LNs of the MCT in group 3; the percentage of mast cells was manually determined for each LN. For group 3, LNs were cytologically categorized with a modified version of a published metastasis categorization scheme. RESULTS Median (range) percentage of mast cells in aspirate samples was 0% (0% to 0.1%) for group 1, 0.05% (0% to 0.55%) for group 2, and 0.4% (0% to 77.4%) for group 3. In group 3, 16 LNs (13 dogs) were palpably normal in size; 6 of these had evidence of possible or certain metastasis. Seven LNs (7 dogs) in group 3 were palpably enlarged, and 5 of these had evidence of certain metastasis. CONCLUSIONS AND CLINICAL RELEVANCE This study provided evidence to support the use of a uniform cytologic grading system to further define nodal metastasis in dogs with MCTs as well as estimates of the percentage of mast cells in LN aspirate samples for healthy dogs and dogs with ADD. Palpably normal LNs in dogs with cutaneous MCT may contain metastasis.

The variability in cytologic findings and frequent presence of dysplastic spindloid cells suggest that cytology alone may not be a reliable tool to differentiate degenerate canine disk material from a mesenchymal neoplasm.

Companion dogs have recently been promoted as an animal model for the study of aging due to their similar disease profile to humans, the sophistication of health assessment and disease diagnosis, and the shared environments with their owners. In addition, dogs show an interesting life history trait pattern where smaller individuals are up to twofold longer lived than their larger counterparts. While some of the mechanisms underlying this size and longevity trade-off are strongly suspected (i.e., growth hormone/IGF-I), there are likely a number of undiscovered mechanisms as well. Accordingly, we have completed a large-scale global metabolomic profiling of dogs encompassing a range of sizes and ages from three cities across the USA. We found a surprisingly strong location signal in the metabolome, stronger in fact than any signal related to age, breed, or sex. However, after controlling for the effects of location, tryptophan metabolism emerged as significantly associated with weight of the dogs, with small dogs having significantly higher levels of tryptophan pathway metabolites. Overall, our results point toward novel, testable hypotheses about the underlying physiological mechanisms that influence size and longevity in the companion dog and suggest that dogs may be useful in sorting out the complexities of the tryptophan metabolic network.

An 11-year-old, Black and Tan Coonhound dog was presented with a history of lameness of the right hind leg for 2 months, osteolysis in the right distal femur, a pulmonary mass, and a presumptive diagnosis of osteosarcoma. By cytologic examination, neoplastic melanocytes were noted from fine needle aspirates of the femoral and pulmonary masses. Postmortem examination revealed a disseminated melanoma involving the right femoral bone marrow, lung, multiple lymph nodes, and adrenal gland, with diffuse infiltration of the leptomeninges of the brain and spinal cord. This case report describes a unique presentation of canine melanoma, which in some ways resembles leptomeningeal melanomatosis, a rare human melanoma variant.