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
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
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
