Subungual tumors of dogs are similar in many respects to tumors of skin, however by convention there are differences in terminology. There are great differences in prognosis.
There are several surveys of digital neoplasms Squamous Cell Carcinoma is usually the most common and melanoma a close second. Marino et al (1995) evaluated 101 neoplasms and included those that were not subungual and this was their list of diagnoses:
Malignant adnexal tumor 2
Adnexal tumor 5
intraosseous epidermoid cyst 3
infiltrating lipoma 2
Marino DJ, Matthiesen DT, Stefanacci JD, Moroff SD. Evaluation of dogs with digit masses: 117 cases (1981-1991). J Am Vet Med Assoc. 1995; 207: 726-728.
O'Brien MG, Berg J, Engler SJ Treatment by Digital Amputation of Subungual Squamous Cell Carcinoma in Dogs: 21 Cases (1987-1988). J Am Vet Med Assoc. 1992; 2015): 759-761.
Paw pad keratoma
These lesions are composed mostly of keratin of the type seen in the pad, but it is excessive and forms a well circumscribed mass.
Subungual epithelial inclusion cyst
These have the typical appearance of an infundibular cyst that increases in size and results in atrophy of the bone of phalynx III.
Squamous cell carcinoma
O'Brien et al (1992) reported on 21 cases all treated with amputation. There was bone invasion in 15, and 1 developed pulmonary metastasis.
Marino et al (1995) reported on 29 cases and reported metastasis in 29%, subungual - better survival 1 yr 95%, 2 yr 74%
Wobester et al (2007) reported on 109 cases and 11 of 42 developed metastatic disease.
Belluco et al (2013) reported on 154 cases. Giant breeds were 75% of 154, 94% had a dark coat. Lesions were mostly front limbs. 49 had followup and 6 died of disease, 2 because of reoccurrence, 4 had probable metastasis and survival <1 year. 11 cases developed new tumors, 14 were confirmed nail bed involvement and 4 had lymphatic emboli
There were no histological features of the primaries to suggest prognosis
Belluco S, Brisebard E, Watrelot D, Pillet E, Marchal T, Ponce F. Digital squamous cell carcinoma in dogs: epidemiological, histological, and immunohistochemical study. Vet Pathol. 2013; 50(6): 1078-1082.
O'Brien MG, Berg J, Engler SJ. Treatment by digital amputation of subungual squamous cell carcinoma in dogs: 21 cases (1987-1988). J Am Vet Med Assoc. 1992; 201: 759-761.
Marino DJ, Matthiesen DT, Stefanacci JD, Moroff SD. Evaluation of dogs with digit masses: 117 cases (1981-1991). J Am Vet Med Assoc 1995; 207: 726-728.
Wobester BK, Kidney BA, Powers BE, Withrow SJ, Mayer MN, Spinato MT, Allen AL. Diagnoses and clinical outcomes associated with surgically amputated canine digits submitted to multiple veterinary diagnostic laboratories Vet Pathol 2007; 44: 355-361
Squamous papilloma - inverted
There is a single case report of an 8 year old dog with a lesion of the distal phalynx and adjacent skin what was composed of variably sized cavernous vascular spaces lined by a single layer of endothelial cells - the typical changes of angiomatosis.
Kuroki K, Britt LG, Franklin SP, Henry CJ(2010) Skeletal–Extraskeletal Angiomatosis in a Dog. Vet Pathol 2010 47: 944-947,
Round Cell Tumors
Carpenter et al (1991) reported on a unique mesenchymal tumor of the digit of 4 dogs. It was a round cell tumor located proximal to the fat pad of a digit. It had multinucleated cells and marked anisokaryosis and was vimentin positive. Stains for histiocytes/macrophages were negative and it was negative for cytokeratins, desmin, S-100 protein, epithelial membrane antigen, alpha-lactalbumin, lysozyme, alpha-1-antichymotrypsin, alpha-lactalbumin, casein, and heavy and light chain immunoglobulins.
Carpenter JL, Dayal Y, King Jr NW, Moore FM. Distinctive Unclassified Mesenchymal Tumor of the Digit of Dogs. Vet Pathol 1991; 28: 396-402
Spangler and Kass (2006) reported on 384 dogs with malignant or benign melanomas and 9 were nailbed tumors.
no treatment differences were taken into account. There were 9 nailbed tumors and all were malignant by behaviour, 4 had mets and 5 died of ‘competing causes.
Nuclear atypia was the most predictive of outcome.
Schultheiss (2006) reported on 27 cases. All were malignant in appearance. Of 14 dogs with survival data, 6 were tumour free after 12 months, and the 8 that died lived for 3-9 months. Size or mitotic count did not correlate with survival.
Schultheiss PC.J Histologic features and clinical outcomes of melanomas of lip, haired skin, and nail bed locations of dogs. J Vet Diagn Invest. 2006; 18: 422-425.
Spangler WL, Kass PH. The histologic and epidemiologic bases for prognostic considerations in canine melanocytic neoplasia. Vet Pathol. 2006 Mar;43(2):136-49.