Veterinary Society of
Surgical Oncology

GENERAL CONSIDERATIONS

General Considerations

  • digit tumors are 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%)
  • 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

MALIGNANT TUMORS

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

General Considerations

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

OTHER DIGIT TUMORS

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, and papilloma

Non-Neoplastic Masses

  • epidermal inclusion cyst
  • calcinosis circumscripta
  • pododermatitis

DIGIT TUMORS

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