Penile and preputial neoplasia

Squamous cell carcinoma

SCC is a common tumor of the penis and prepuce in horses. The clitoris can also be affected. SCC is common in older geldings, particularly those with unpigmented preputial/penile skin (Appaloosas and Paints). SCC has been associated with chronic irritation due to smegma. Horses with ocular SCC should be checked for urogenital SCC as well and vice versa.

SCC can appear as several small lesions (papillomas), ulcers, plaques or granulomatous cauliflower-like lesions. The glans and urethral opening are often affected. Tumors tend to be locally invasive and, while slow to metastasize, can spread to regional lymph nodes. A rectal examination can be useful to detect spread to sublumbar lymph nodes. Deep palpation of the inguinal area can detect enlargement of those nodes (easiest when the horse is anesthetized).

Lymph node aspiration is recommended; enlarged nodes may be due to metastasis or inflammation.

Differential diagnoses should include papillomas and habronemiasis. Benign papillomas may progress into malignant SCC.

Treatment options are the same as for SCC at other sites. The most commonly used treatments include cryotherapy, CO2 laser resection, topical 5-fluorouracil, and resection.

Cryotherapy

Cryotherapy can be performed in the standing horse using sedation +/- local anesthesia. After the initial freeze, the area is relatively numb and local anesthesia is not commonly used. A double to triple freeze-thaw cycle is used at a minimum, with a quick freeze and a slow thaw preferred for the most cellular damage. When you have frozen it enough, the area stays “frozen” and doesn’t thaw rapidly anymore.

Because this is a mucous membrane, the probe can “stick”. Have water ready to apply if the probe is difficult to remove.

Do not freeze where scars may squeeze. Avoid freezing the urethral opening and be careful around the glans.

Cryotherapy is most useful for small lesions or following debulking. It is often used to control recurrence and may be combined with other treatments (eg 5 FU).

5-Fluorouracil

5-FU is a topical chemotherapeutic agent that interferes with the cell’s ability to synthesize DNA. Repeated application can lead to tumor remission. The drug is much less toxic when applied topically as opposed to systemic administration.

5-FU is applied after surgical debridement or to small lesions. In mares, daily application is necessary. Recheck mares every 2 weeks until remission and then every 6 months. In geldings/ stallions, the sheath maintains a higher drug concentration and 5FU is applied every 2 weeks. An inflammatory response is expected beginning at 5-7 days and continues through 2-4 weeks. The tumor sloughs at 6-12 weeks in many cases. Therapy often involves 3-6 treatments but should be continued until the tumor is under control.

5-FU can be obtained from most human pharmacies and comes in small tubes that aren’t cheap. If a tumor is debulked, you may want to wait until bleeding stops before applying 5FU to ensure that it isn’t washed away.

Many horses need continued treatment at least 1-2x a year. 5-FU can be used indefinitely but does eventually affect normal skin cells (since they are rapidly dividing). The irritation can lead to epithelial changes (and tumor formation?).

Cisplatin beads

A new treatment and relatively inexpensive. One bead implanted per cm.2

CO2 Laser

The CO2 laser is useful for removing skin tumors, including urogenital lesions. The shallow cutting action and limited lateral damage of this laser make it easy to “shave” tumors off until normal tissue is apparent with minimal inflammatory response. Laser treatment can be performed in the standing animal using local anesthetic and sedation. The laser also decreases nerve sensation and seems to have less postoperative pain associated than does cryotherapy. Tumor recurrence can be more difficult to detect as it may be covered by normal skin.

Tumor resection

Besides the option of removing a local lesion (can be done standing with local anesthesia and primary closure of the defect; get wide margins), tumor resection may involve removal of the prepuce or part/all of the penis or clitoris. With clitoral SCC, extensive dissection and wide margins are required.

Posthioplasty or Reefing

In this procedure, the superficial mucosal layer of the prepuce is removed (and hopefully the tumor along with it) and the remaining ends reanastomosed. The procedure is most commonly done under general anesthesia but is short enough to be done under injectable anesthesia.

Circumferential incisions are made in the prepuce on either side of the lesion and connected by a longitudinal incision. Marking sutures may be placed on the outside edges of the circumferential incisions to make sure the tissues aren’t twisted. A penrose drain placed proximally works well as a tourniquet. The mucosa between the circumferential incisions is peeled off underlying tissues with sharp and blunt dissection. The remaining mucosal edges of the prepuce are re-anastomosed with short continuous suture patterns, usually with absorbable 2-0 suture.

Postoperative care involves NSAIDs to minimize swelling +/- oral antibiotics (not the cleanest area).

Phallectomy (penile amputation)

There is a limit to how much penis can be physically removed.

This procedure should not be done in intact stallions as erection can result in wound dehiscence and hemorrhage. Stallions should be castrated at least 2 weeks prior to phallectomy.

Complications include urethral swelling and obstruction (maximum at 3-4 days); dehiscence (partial usually heals okay), and tumor recurrence or incomplete removal (25.6% recurrence rate; biopsy margins at surgery; apply 5FU, etc).

Budget cases: can amputate standing using a Callicrate bander; need to perform a PU so they can urinate. Penis undergoes ischemic necrosis. Might be difficult for some owners to handle.

En bloc resection and penile retroversion

Rarely done anymore due to extensive complications and aftercare required.

Amputation and sheath ablation

This is a newer procedure to retain more normal orientation of the penis. A new skin opening is made in the ventral abdomen and a urethrostomy performed at the new site. Pain occurs if too much traction is present (assess likely sx site when horse is standing), hemorrhage and dehiscence are possible. Urine scald is reportedly not as severe. Lymph nodes can be removed through separate incisions. Better owner acceptability? (most commonly recommended right now)

With all of these treatments, reevaluation and sheath cleaning is recommended at least every 6 months for cases of SCC.

 Sarcoids

Sarcoids can occur on the preputial skin. Treatment is the same as for treatment of sarcoids in other sites. Aldara, cryotherapy, cisplatin beads and/or laser removal are the most common recommendations at this time.

Other tumors

Melanomas are common in the sheath of gray horses. Treatment is not usually required.

Very rarely are these tumors malignant, however, malignancy and metastasis has been reported. Lymphosarcoma can also develop in the sheath. Systemic steroids can help control the disease. Hemangiosarcoma has been reported. Papillomatosis is usually self limiting but persistent cases have been reported. May be a precursor to SCC.