Squamous Cell Carcinoma : Early Detection Makes a Difference

A pony presented with a non-healing ulcerated wound just next to and extending below her vulva. The pony was treated with systemic antibiotics and topical medication, but the wound did not completely resolve. After a thorough evaluation, I recommended immediate surgical removal and that instinct proved correct.

The mare was sedated and I carefully excised the mass, prioritizing clear surgical margins meaning the tumor was fully surrounded by healthy tissue on all sides at the time of removal. The excised tissue was then submitted for histopathology, and results confirmed what I had suspected: Squamous Cell Carcinoma (SCC).

Indicating the location of the suspected Squamous Cell Carcinoma

The suspected Squamous Cell Carcinoma prior to removal.

What Is Squamous Cell Carcinoma?

Squamous Cell Carcinoma is the second most common tumor in horses, behind sarcoids. It is a malignant cancer originating in squamous epithelial cells. The epithelial  cells line the skin surface and mucosal junctions throughout the body.

SCC has a particular affinity for areas where skin meets mucous membrane, which is why it so frequently appears around the genitalia, eyes, and mouth. In mares, the vulva and perineal region are among the most common sites.

SCC can present in two ways:

•       Proliferative: A raised, cauliflower-like or nodular mass growing outward from the tissue

•       Ulcerative: An open, eroded lesion — often bleeding, oozing, or with an unpleasant odor

Without treatment, SCC is locally invasive and can spread to regional lymph nodes and, in advanced cases, to other organs. Early diagnosis and intervention dramatically improve outcomes.

Ponies Are Not Exempt

During surgical removal

It's easy to assume that cancer is primarily a concern for older, full-sized sport horses. This case is a reminder that equine SCC does not discriminate by size or breed. Small ponies, backyard horses, and pleasure animals are just as vulnerable  and may actually go longer without routine veterinary evaluation, which can allow tumors to grow undetected.

What Horse Owners Should Watch For

Be proactive. Do a visual check of these areas during regular grooming:

•       Unexplained lumps, growths, or swelling near the vulva, perineum, or base of the tail

•       Sores or wounds in the genital area that fail to heal normally

•       Unexplained bleeding, discharge, or unusual odor

•       Pink, raised, or irritated tissue around the eyes or mouth

•       Any change in skin texture or color at skin-to-mucosa junctions

When in doubt, call your veterinarian. A lump that turns out to be benign costs you peace of mind. A lump left unchecked could cost your horse much more.

Treatment: Why Clear Margins Matter

Surgical excision with wide, clear margins is the gold standard treatment for SCC when the tumor's size and location allow for it. The objective is to remove all cancerous tissue  including a surrounding border of healthy cells with the goal of minimizing the risk of recurrence.

The suspected SCC after removal prior to being sent to a pathology laboratory for histopathologic evaluation.

Following removal, the tissue is sent to a pathology laboratory for histopathologic evaluation. This step confirms the diagnosis, identifies the tumor type, and critically  assesses whether the surgical margins are truly clear. It transforms a clinical suspicion into a confirmed diagnosis and gives the veterinary team and owner the information needed to plan next steps.

In some cases, additional treatment such as topical chemotherapy (5-fluorouracil), cryotherapy, or laser ablation may be recommended alongside or following surgery, particularly if margins are tight or recurrence occurs.

Cases like this one reinforce why routine veterinary exams and owner awareness are so essential.

30 Days Later: A Clean Bill of Health

This little mare's recovery was nothing short of excellent. At her 30-day post-operative

30 Days Post Surgery

recheck, she was healing beautifully with no complications, no signs of infection, and most importantly, histopathology confirmed clear surgical margins, meaning the tumor had been fully removed. She experienced no issues following surgery and bounced back remarkably well.