21b: Equine Skin Tumors

Second most common tumor in horses

SCC

General predilection sites for SCC

• Non-pigmented skin

• Mucocutaneous junctions

• Areas without hair

Common sites for SCC in horses

Eyes/conjunctiva and external genitals

Characteristics of SCC in horses

Locally malignant and invasive, but doesn’t tent do metastasize

Types of SCC

Ulcerative or proliferative

Predisposing factors for SCC in horses

• Genetics

• UV exposure

• Chronic irritation

• Virus

• Older horses

Breed predisposed to getting equine SCC

Paints

Virus associated with most equine genital SCC

Equus caballus papillomavirus-2

Treatment method that is used for SCC basically before any other method

Surgical excision/debulking

Treatment method that is considered the gold standard for carcinomas (esp. periocular)

Radiotherapy

Radiotherapy mechanism of action

Damages cell DNA → interrupts replication and mitosis

Types of radiotherapy

• Teletherapy/external beam radiation therapy

• Plesiotherapy (topical)

• Interstitial brachytherapy

Common intralesional chemotherapeutics for SCC

• Cisplatin + oil/water

• 5-FU

Common topical chemotherapeutics for equine SCC

• 5-FU

• Mitomycin C (specifically for ocular!)

Systemic chemotherapeutic that may be used for equine SCC

Piroxicam

T/F: piroxicam is used as a monotherapy for SCC

F, it is often an adjunct therapy

Types of horses more likely to get melanomas

Gray horses

Side predilections for equine melanoma

• Perineum

• Base of tai

• Head

• Parotid

Types of equine melanom

• Melanocytic nevi

• Dermal melanoma

• Dermal melanomatosis

• Malignant melanoma

Melanocytic nevi

Single or multiple discrete nodules

Dermal melanoma

Small single/multiple nodules in the deeper dermis

Dermal melanomatosis

Confluent, multiple large melanomas

Malignant melanoma

Rare, very invasive

Types of equine melanoma that are benign on histo with no visible mitosis

Dermal melanoma and dermal melanomatosis

Great first line of treatment for melanomas that are not affecting quality of life or intended use

Benign neglect

For which type of equine melanomas is surgery typically curative

Melanocytic nevi and dermal melanomas

Cimetidine MOA for treatment of melanoma

Histamine receptor antagonist → immune modulation and antitumor activity

Intralesional chemo used for equine melanoma

• Cisplatin

• 5-FU

Efficacy of melanoma vaccines

Variable

Melanoma vaccine MOA

Uses surface Ags from tumor tissue to stimulate an immune response directed against the melanoma

Less common skin tumors in horses

Mast cell tumors and lipomas

If a horse has a MCT, what is it likely to look like

Solitary, benign cutaneous nodule

Treatment for equine MCT

Surgery

Treatment for equine lipoma

Often we leave it, but you can do surgery if the owners really want it