Page 91 - Differential Diagnosis in Small Animal Cytology, The Skin and Subcutis

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8.1 Tumours without Squamous or Adnexal Differentiation
VetBooks.ir Basal cell tumour and basal cell carcinoma

Tumours that originate from the basal cells of the epidermis and do not show squamous or
adnexal differentiation.

Clinical features
Following the 1998 World Health Organization (WHO) classification system, all tumours
that were previously diagnosed as basal cell tumours were reclassified as either trichoblasto-
mas or sweat gland adenomas. The new classification published by the David-Thompson
DVM Foundation (Goldschmidt et al., 2018) has reintroduced this tumour as a separate
entity. Due to this, little is known about the true incidence, presentation and clinical behav-
iour of this tumour nowadays. The clinical information described below goes back to the
studies performed before the 1998 WHO classification.
• Basal cell tumour (cats):
• Benign tumour that arises from the basal cells of the epidermis.
• Age: peak incidence between 6 and 13 years old.
• Lesions are well circumscribed, can be alopecic, ulcerated and pigmented.
• Most commonly reported on the head and neck.
• Incomplete excision may result in tumour recurrence.
• It is unknown if this tumour can progress to basal cell carcinoma.
• Basal cell carcinoma:
• Age: peak incidence between 12 and 16 years old.
• Usually appears as a thick plaque. It can be ulcerated and can infiltrate the dermis.
It can be pigmented or non-pigmented.
• Low-grade malignancy, thought to be rare in dogs and cats. Surgical excision is
generally curative and metastases are very rare but have been reported.
• Infiltrative forms may recur after surgical excision.
• Over-represented feline breed: Ragdoll cat.

Cytological features
• Cellularity is variable, generally moderate.
• Background: variably haemodiluted.
• The aspirates are composed of cuboidal epithelial cells in uniform and cohesive clusters,
both seen in benign and malignant forms.
• Nuclei are small to medium sized and round. The chromatin is clumped and nucleoli are
not seen.
• The cytoplasm is scant and moderately basophilic, often with indistinct borders. It often
contains dark granules (melanin pigment).
• Anisokaryosis and anisocytosis are minimal in benign forms and could become more prominent
in carcinomas. The N:C ratio is high.