Subungual Squamous Cell Carcinoma

Supported by the Savannah and Barry French Poodle Memorial Fund
University of Pennsylvania School of Veterinary Medicine
Last Modified: August 21, 2005

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Michael H. Goldschmidt, MSc, BVMS, MRCVS, Diplomate ACVP Professor and Head, Laboratory of Pathology and Toxicology Chief, Surgical Pathology Department of Pathobiology
Frances S. Shofer, PhD, Adjunct Associate Professor of Epidemiology and Biostatistics

Introduction

Definition: A malignant tumor of epidermal cells with varying degrees of keratinocyte (squamous cell) differentiation

Synonyms: digital squamous cell carcinoma

Subungual SCC involves the nailbed of the canine paw. These tumors are most often solitary neoplasms, although multiple tumors on different digits have been found on some dogs.

Etiology/Epidemiology

Whereas cutaneous squamous cell carcinoma is associated with ultraviolet light exposure, there is no such association with subungual squamous cell carcinomas. However, the relationship between previous papilloma virus infection and subsequent development of subungual squamous cell carcinomas awaits further investigation.

Sex N Percent
Female 251 17% (21%)
Female Spayed 523 36% (33%)
Male 378 26% (25%)
Male Castrated 306 21% (21%)
(Normal Population %)

Breeds at
Increased Risk
N Probability OR 95% Confidence
Interval
Giant Schnauzer 37 <0.0001 22.7 16.0 32.3
Gordon Setter 28 <0.0001 11.1 7.5 16.3
Briard 10 <0.0001 10.4 5.5 19.8
Kerry Blue Terrier 19 <0.0001 7.7 4.8 12.2
Standard Poodle 96 <0.0001 5.9 4.8 7.2
Rottweiler 166 <0.0001 5.7 4.8 6.7
Flat Coated Retriever 5 0.00530 4.6 1.9 11.3
Scottish Terrier 42 <0.0001 4.2 3.1 5.7
Standard Schnauzer 41 <0.0001 3.8 2.8 5.2
Afghan Hound 9 0.00190 3.4 1.7 6.5
Dachshund 40 <0.0001 2.2 1.6 3.0
Labrador Retriever 214 <0.0001 2.0 1.7 2.3

Breeds at
Decreased Risk
N Probability OR 95% Confidence
Interval
German Shepherd 41 0.01170 0.67 0.49 0.92
Husky 9 0.00550 0.42 0.22 0.81
Golden Retriever 43 <0.0001 0.40 0.30 0.54
Lhasa Apso 5 0.00750 0.37 0.17 0.83
Yorkshire Terrier 6 0.00250 0.33 0.15 0.74
English Springer Spaniel 9 0.00019 0.30 0.14 0.63
Basset Hound 4 0.00210 0.27 0.10 0.73
Boston Terrier 2 0.02940 0.25 0.06 1.01
Boxer 10 <0.0001 0.23 0.13 0.43
Shetland Sheepdog 5 <0.0001 0.18 0.07 0.42
Collie 2 0.00076 0.16 0.04 0.65
Maltese 1 0.01780 0.15 0.02 1.07
Samoyed 1 0.01830 0.15 0.02 1.03
Beagle 3 <0.0001 0.10 0.03 0.30

OncoLink Veterinary Cancer Resources

Clinical Presentation/Physical Exam Findings

  • Subungual SCC is frequently diagnosed in the advanced stages of disease.
  • A single digit or multiple digits on the same animal may be affected.
  • The dog may present with:
    • a nail deformity
    • paronychia (inflammation of the tissue surrounding the nail)
    • chronic fissuring
    • inflammation
  • In later stages of the disease, loss of the nail or growth of a mass from the nail bed may be seen.
  • Secondary infections may be seen at the site of nail loss.
  • Radiographic evaluation of the affected digit will often show lysis of part or all of P3.

Differential Diagnoses: keratoacanthoma, inverted papilloma, malignant melanoma, infectious (bacterial or fungal)

Tumor Pathology

Gross Findings

  • Bone destruction of P3
  • Tumor destruction may extend into the joint space between P3 and P2.
  • Tumor tissue is grey/yellow, soft, friable, and may be easily differentiated from the surrounding bone.
  • The nail and skin are pigmented, but the tumor is not.

Microscopic Findings

  • Histopathology is identical to that described for cutaneous squamous cell carcinomas.
  • Infiltrating islands of squamous epithelium extend from the nailbed and invade into the medullary and cortical bone of P3.

Clinical Behavior

These tumors usually require digital amputation at the proximal part of P1. If such tumors recur, it is probably due to tumor invasion into the bursa of the extensor and flexor tendons found on the metacarpus/metatarsus. Metastasis to regional lymph nodes and lungs via lymphatics is not common.

References

  • Goldschmidt, M.H., & Hendrick, M.J. (2002). Tumors of the skin and soft tissue. In D.J. Meuten (Ed.), Tumors in domestic animals 4 th ed (pp. 45-119). Iowa: Iowa State Press
  • Goldschmidt, M.H., & Shofer, F.S. (1998). Skin tumors of the dog and cat. Woburn, MA: Butterworth-Heinemann
  • Gross, T.L., Ihrke, P.J., & Walder, E.J. (1992). Veterinary dermatopathology: A macroscopic and microscopic evaluation of canine and feline skin disease. (pp. 327-485). St. Louis, Missouri: Mosby Year Book
  • World Health Organization (1998). Histological classification of epithelial and melanocytic tumors of the skin of domestic animals (2 nd series, vol 3). Washington, DC: Armed Forces Institute of Pathology
  • Yager, J.A. & Wilcock, B.P. (1994). Color atlas and text of surgical pathology of the dog and cat. Ontario, Canada: Mosby Year Book



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