Clinical Features and Outcome of 79 Dogs With Digital Squamous Cell Carcinoma Undergoing Treatment: A SIONCOV Observational Study

Abstract

In dogs, digit squamous cell carcinoma (SCC) is uncommon. Clinical signs are frequently underestimated, leading to a diagnostic delay. The purpose of this retrospective study was to report our experience regarding the clinical presentation, diagnostic work-up, treatment and outcome of 79 client-owned dogs with SCC of the digit. The greatest majority (84.8%) of dogs was dark-coated. Schnauzers represented approximately one third of the study population, and had a poorer outcome compared with other breeds. The majority of SCCs occurred in the front limbs (61%), and bone lysis was frequently observed (92.4%). Approximately 9% of dogs had involvement of multiple digits, and this was associated with a shorter time to progression (TTP; P = 0.047). Similarly, a duration of clinical signs >90 days was associated with a shorter TTP (P = 0.02). Regional lymph node metastases were documented in 17.7% of dogs at admission and were significantly associated with tumor-related death (P < 0.001). At presentation, none of the dogs had evidence of distant metastasis. Digit amputation achieved adequate local tumor control in the majority of cases. Adjuvant chemotherapy and radiation therapy were carried out in 21.5% of cases, with uncertain benefit. Due to the relatively non-aggressive clinical behavior of digit SCC, chemotherapy should only be offered in the case of metastatic disease. Approximately one fourth of dogs developed de novo SCCs during the follow-up. Careful examination of the digits should be encouraged in breeds considered at high risk and in dogs with a previous history of digital SCC.

Radiographic features of subungual keratoacanthomas in dogs

“…In dogs, digital osteolysis is commonly considered to be a characteristic of malignant neoplasms, such as SCC. 6,8 Digital osteolysis can also be present with SK and was identified in all of our cases. Phalangeal osteolysis in dogs with SK is considered to be secondary to pressure osteonecrosis from the adjacent tumor, leading to smooth osteolytic margins and a short area of transition with normal bone.…”

“…In dogs, digital osteolysis is commonly considered to be a characteristic of malignant neoplasms, such as SCC 6,8 . Digital osteolysis can also be present with SK and was identified in all of our cases.…”

“…2,3 SCC, by comparison, tends to be more commonly ulcerative, can affect multiple digits, and displays more aggressive local invasion (e.g., extending into the proximal phalanx), in addition to having metastatic potential. 1,3,6,8,9,11 Moreover, SCC can cause new bone formation, which was not a feature of SK in this study or previously published case reports. 3,6 Benign processes such as pododermatitis, folliculosebaceous hamartoma, and intraosseous epidermoid cysts should also not be completely ruled out when presented with radiographs of digital mass-forming lesions, as they can also cause osteolysis of the distal phalanx.…”

“…In cases of SK, ulceration of the adjacent epidermis and secondary infection are infrequently encountered 2,3 . SCC, by comparison, tends to be more commonly ulcerative, can affect multiple digits, and displays more aggressive local invasion (e.g., extending into the proximal phalanx), in addition to having metastatic potential 1,3,6,8,9,11 . Moreover, SCC can cause new bone formation, which was not a feature of SK in this study or previously published case reports 3,6 .…”

KITLG Copy Number Germline Variations in Schnauzer Breeds and Their Relevance in Digital Squamous Cell Carcinoma in Black Giant Schnauzers

“…There may be lameness, thickening of the toes, and ulceration of the digital tissue. The nail material often appears softened and frayed [ 5 ]. Most commonly, the forelimbs are affected, and the mean age of the canine patients is about 10 years [ 4 , 5 , 6 ].…”