+ General Considerations

  • Hair follicle tumors account for < 1% of skin tumors in cats and 5% of canine skin tumors
  • Types: trichoepithelioma, pilomatrixoma, tricholemmoma, and trichofolliculoma

+ Trichoepithelioma (Hair Matrixoma)

  • Trichoepithelioma accounts for 80% of hair follicle tumors (and up to 2%-3% of all feline skin tumors)
  • Benign tumor derived from primitive hair matrix cells that show differentiation to either mature or incompletely developed hair follicles
  • 17.5% have histologic features of malignancy
  • However, biologic behaviour is usually benign with local tumor recurrence and metastasis rare
  • Site: dorsal lumbar and lateral thoracic region
  • Gross appearance is similar to basal cell carcinoma but some are cystic and contain keratin
  • Intradermal mass with overlying epidermis atrophic, hairless and often ulcerated secondary to trauma
  • Treatment: surgery
  • Prognosis: excellent

+ Feline Trichoepithelioma

  • Breed predisposition: Siamese
  • In cats, trichoepithelioma is well-circumscribed, > 5 cm in diameter and usually occur over dorsal lumbar area although others report small, slow-growing tumors with a predilection for the head and back

+ Canine Trichoepithelioma

  • Mean age 9.3 years
  • Breed predisposition: Golden Retriever, GSD, and Bassett Hound
  • Histologically unique form with mucinous degeneration reported in the Golden Retriever

+ Pilomatricoma

  • Benign tumors arising from hair matrix cells and particularly pilar matrix cells
  • Mean age 8.2 years
  • Breed predisposition: Kerry Blue Terrier and Miniature Poodle
  • Sites: shoulder and lumbrosacral region
  • Slow growing, well-encapsulated, and often mineralized with 33% cystic and 33% hyperpigmented
  • Malignant pilomatricoma is rare (2 cases reported) with metastasis to neurologic structures
  • Treatment: surgery
  • Prognosis: excellent

+ Tricholemmoma and Trichofolliculoma