+ General Considerations

  • Rare in cats and common in dogs
  • Digit masses: 61% are malignant tumors, 20% are benign tumors, and 19% are pyogranulomatous inflammation
  • 12% of nail and nail bed diseases are tumors
  • Digit masses include SCC (33%-54%), malignant melanoma (11%), STS (9%), and OSA (6%)
  • Others digit masses include MCT, epidermoid cyst, plasmacytoma, HSA, and calcinosis circumscripta
  • Black the most common colour coat for dogs with digit masses

+ Survey Radiographs

  • Osteolysis is more commonly associated with tumors, but it is difficult to differentiate malignant tumors from pododermatitis and benign tumors
  • Bone lysis can be caused by malignant tumor (83%) or benign tumor or pyogranulomatous inflammation (17%)

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  • Benign tumors causing bone lysis include intraosseous epidermoid cyst and infiltrating lipoma
  • Tumors and non-neoplastic masses associated with soft tissue swelling and no bone involvement include MCT, solitary plasmacytoma, STS, sebaceous gland ADC, histiocytoma, papilloma, and calcinosis circumscripta
  • Inflammatory changes tend to be proliferative whereas neoplastic changes are usually destructive
  • Pressure erosion and infarcts common in adjacent bone

+ General Considerations

  • Single digit: solitary plasmacytoma, STS, OSA, and carcinoma
  • Digits and metatarsus: synovial cell sarcoma and ADC
  • Multiple digits: solitary plasmacytoma, synovial cell sarcoma, ADC and carcinoma

Squamous Cell Carcinoma

+ Survey Radiographs

  • Digit SCC arise from the subungual epithelium
  • Digit SCC are usually solitary, ulcerative, and expansile with occasional hemorrhage

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  • Multiple digit SCC have been reported in 3 related Giant Schnauzers
  • Biologic behaviour: locally invasive with low-to-moderate metastatic potential
  • Bone invasion detected in 80% of digit SCC

+ Clinical Features

  • Mean age: 9 years
  • No sex predilection
  • 75% are large breed dogs
  • 67%-71% occur in dogs with black coats (i.e., Labrador Retriever and Standard Poodle)
  • Treatment: digit amputation (to metacarpophalangeal, metatarsophalangeal, or proximal interphalangeal level)

+ Prognosis

  • Prognosis is guarded with reports on digit SCC varying widely
  • 5%-29% metastatic rate to regional lymph nodes and lungs, including 13% metastatic at presentation
  • 1-year survival rate 60%-95%
  • 2-year survival rate 20%-74%
  • However, tumor-related deaths are rare (4.7%, 1/21)
  • Prognostic factors include region of digit involved and surgical dose:
  • SCC arising from subungual has a significantly better survival rate than other areas of the digit (1-year survival rate 95% v 60%, and 2-year survival rate 74% v 44%)
  • Marginal resection is associated with an increased local tumor recurrence rate

+ Melanoma

  • 50% are benign melanocytic nevi and 50% malignant melanoma
  • Melanocytic nevi are not associated with local tumor recurrence or metastasis following surgical excision
  • Bone lysis is detected in 5% of digit melanoma
  • Prognosis is guarded because of a high distant metastatic rate
  • Local recurrence rate 14%-30%
  • Distant metastatic rate 58%-71% to regional lymph node and lungs, including 32% at diagnosis
  • MST 12 months with:
  • 1-year survival rate 42%-66%
  • 2-year survival rate 12%-22%

+ Soft Tissue Sarcoma

  • Biologic behaviour similar to other sites
  • Treatment: digit amputation

+ Mast Cell Tumor

  • Subungual MCT are usually grade III MCT with a similar prognosis to other mucocutaneous junction MCT
  • Digit sites other than subungual have a similar biologic behaviour to other cutaneous MCT
  • Prognosis: MST 20 months with 1-year survival rate 88% and 2-year survival rate 50%

+ Osteosarcoma Distal to the Carpus and Tarsus

  • Treatment: digit amputation and postoperative chemotherapy
  • MST 466 days with euthanasia because of metastatic disease
  • Prognosis better than OSA in other appendicular sites
  • However, digit OSA is still a malignant tumor with high metastatic potential
  • Surgical excision of OSA distal to the carpus or tarsus in humans usually results in an excellent prognosis


+ Feline Digit Tumors

  • Subungual tumors are rare
  • Acrometastasis is relatively common with multiple digit involvement with primary bronchoalveolar ADC or SCC ± cutaneous SCC

+ Footpad Tumors

  • Eccrine tumors are rare
  • Eccrine tumors are usually malignant in cats, but can be benign or malignant in dogs
  • Clinical signs: lameness and swelling of multiple digits
  • Gross appearance: poorly defined swelling of the footpad or digit with ulceration and may involve multiple digits
  • Survey radiographs: bone lysis is common
  • Eccrine ADC is aggressive with early metastasis to regional lymph node and lungs
  • DDx: SCC, keratoacanthoma, malignant melanoma, OSA, LSA, and HSA

+ Benign Tumors

  • Histiocytoma
  • Lipoma (infiltrative and non-infiltrative)
  • Osteochondroma
  • Papilloma

+ Non-Neoplastic Masses

  • Epidermal inclusion cyst
  • Calcinosis circumscripta
  • Pododermatitis