Summary
Medical records of 117 dogs with digit masses were reviewed. Of 124 digit masses, 76 (61%) were malignant neoplasms, 25 (20%) were benign neoplasms, and 23 (19%) were pyogranulomatous inflammation. Of 29 digits with radiographic evidence of bone lysis, 24 (83%) were affected by malignant masses, whereas only 5 of 29 (17%) digits with radiographic evidence of bone lysis were affected by benign or pyogranulomatous masses. Only 1 of 19 (5%) dogs with melanoma had radiographic evidence of lysis, but 20 of 25 (80%) dogs with squamous cell carcinoma had radiographic evidence of bone lysis. Thoracic radiographs of 95 dogs were available. Six of 19 (32%) dogs with melanoma had radiographic evidence of pulmonary metastasis at the time of diagnosis, whereas 3 of 24 (13%) dogs with squamous cell carcinoma had radiographic evidence of pulmonary metastasis at the time of diagnosis. Twenty-nine digit neoplasms were squamous cell carcinoma, and 19 of 29 (66%) arose from the subungual epithelium. Of 19 dogs with squamous cell carcinoma originating from the subungual epithelium, 18 (95%) survived for at least 1 year, whereas only 6 of 10 (60%) dogs with squamous cell carcinoma originating in other parts of the digit survived for at least 1 year. Furthermore, of 19 dogs with squamous cell carcinoma originating from the subungual epithelium, 14 (74%) survived at least 2 years, whereas only 4 of 9 (44%) dogs with squamous cell carcinoma originating in other parts of the digit survived for 2 years. Dogs with melanoma of the digits had a median survival time of 12 months, with 10 of 24 (42%) alive at 1 year and 3 of 23 (13%) alive at 2 years. Dogs with mast cell tumor of the digits had a median survival time of 20 months, with 7 of 8 (88%) dogs alive at 1 year and 4 of 8 (50%) alive at 2 years.
Analysis of the results of the study reported here indicated that the prevalence of neoplasms in dogs with digit masses was high. Malignant neoplasms were more prevalent than benign neoplasms, with the most commonly identified types being squamous cell carcinoma and melanoma. Radiographic evidence of bone lysis was seen in dogs with all types of masses but was more commonly associated with squamous cell carcinoma than with melanoma. Dogs with melanoma of the digit had a higher prevalence of pulmonary metastasis and a poorer prognosis than dogs with squamous cell carcinoma.
