Armed Forces Institute of Pathology (AFIP) - Department of Veterinary PathologyY

Histological Classification of Epithelial and Melanocytic Tumors of the Skin of Domestic Animals

1 Epithelial Tumors without Squamous or Adnexal Differentiation

1.1 Basal cell tumor (basal cell epithelioma)
1.2 Basal cell carcinoma

1.2.1 Infiltrative
1.2.2 Clear cell
2 Tumors of the Epidermis

2.1 Benign

2.1.1 Papilloma (papillomatosis)
2.1.2 Inverted papilloma

2.2 Malignant

2.2.1 Actinic keratosis (solar keratosis)
2.2.2 Multicentric squamous cell carcinoma in situ (Bowen-like disease)
2.2.3 Squamous cell carcinoma
2.2.4 Basosquamous carcinoma
3 Tumors with Adnexal Differentiation

3.1 Follicular tumors

3.1.1 Infundibular keratinizing acanthoma (intra-cutaneous cornifying epithelioma, keratoacanthoma)
3.1.2 Tricholemmoma

3.1.2.1 Inferior
3.1.2.2 Isthmic

3.1.3 Trichoblastoma

3.1.3.1 Ribbon
3.1.3.2 Trabecular
3.1.3.3 Granular cell
3.1.3.4 Spindle

3.1.4 Trichoepithelioma
3.1.5 Malignant trichoepithelioma (matrical carcinoma)
3.1.6 Pilomatricoma (pilomatrixoma, necrotizing and calcifying epithelioma of Malherbe)
3.1.7 Malignant pilomatricoma (pilomatrix carcinoma)

3.2 Nailbed tumors

3.2.1 Subungual keratoacanthoma (nailbed keratoacanthoma)
3.2.2 Subungual squamous cell carcinoma (nailbed squamous cell carcinoma)

3.3 Sebaceous and modified sebaceous gland tumors

3.3.1 Sebaceous adenoma
3.3.2 Sebaceous ductal adenoma
3.3.3 Sebaceous epithelioma
3.3.4 Sebaceous carcinoma
3.3.5 Meibomian adenoma
3.3.6 Meibomian ductal adenoma
3.3.7 Meibomian epithelioma
3.3.8 Meibomian carcinoma
3.3.9 Hepatoid gland adenoma (perianal gland adenoma, circumanal gland adenoma)
3.3.10 Hepatoid gland epithelioma (perianal gland epithelioma, circumanal gland epithelioma)
3.3.11 Hepatoid gland carcinoma (perianal gland carcinoma, circumanal gland carcinoma)

3.4 Apocrine and modified apocrine gland tumors

3.4.1 Apocrine adenoma
3.4.2 Complex and mixed apocrine adenoma
3.4.3 Apocrine ductal adenoma
3.4.4 Apocrine carcinoma
3.4.5 Complex and mixed apocrine carcinoma
3.4.6 Apocrine ductal carcinoma
3.4.7 Ceruminous adenoma
3.4.8 Complex and mixed ceruminous adenoma
3.4.9 Ceruminous gland carcinoma
3.4.10 Complex and mixed ceruminous carcinoma
3.4.11 Anal sac gland adenoma (adenoma of the apocrine glands of the anal sac)
3.4.12 Anal sac gland carcinoma (carcinoma of the apocrine glands of the anal sac)

3.5 Eccrine (atrichial) tumors

3.5.1 Eccrine adenoma
3.5.2 Eccrine carcinoma
4 Tumors Metastatic to the Skin
5 Cysts

5.1 Infundibular cyst (epidermoid cyst, epidermal cyst, epidermal inclusion cyst)
5.2 Dilated pore
5.3 Isthmus cyst
5.4 Panfollicular (trichoepitheliomatous) cyst
5.5 Dermoid cyst (dermoid sinus)
5.6 Sebaceous duct cyst
5.7 Apocrine cyst(s) (apocrine cystomatosis)
5.8 Ciliated cyst
5.9 Subungual epithelial inclusion cyst
6 Hamartomas

6.1 Epidermal hamartoma (pigmented epidermal nevus)
6.2 Follicular hamartoma
6.3 Sebaceous hamartoma
6.4 Apocrine hamartoma
6.5 Fibroadnexal hamartoma (adnexal nevus, focal adnexal dysplasia, folliculosebaceous hamartoma)
7 Tumor-like Lesions

7.1 Squamous papilloma
7.2 Pressure point comedones
7.3 Cutaneous horn
7.4 Warty dyskeratoma
7.5 Sebaceous hyperplasia (senile nodular sebaceous hyperplasia)
7.6 Fibroepithelial "polyp" (cutaneous tag, skin tag, acrochordon)
7.7 Fibropruritic nodule (acral lick granuloma)
8 Melanocytic Tumors

8.1 Melanocytoma (dermal melanoma, benign melanoma)
8.2 Melanoacanthoma
8.3 Malignant melanoma
8.4 Melanocytic hyperplasia (lentigo, lentigo simplex)