Bioabsorbable Cisplatin Beads for Skin Cancers

Skin cancers are seen in horses, and many methods and technologies have been used to treat them. One of the more recent strategies is intralesional chemotherapy, or placing a chemotherapeutic agent directly in the tumor to kill the abnormal cells. At the 2007 American Association of Equine Practitioners Convention, held Dec. 1-5 in Orlando, Fla., Christina Hewes, DVM, MS, Dipl. ACVS, a practitioner in Alamo, Calif., discussed the newest twist on this approach--placing bioabsorbable beads of the chemotherapeutic agent cisplatin in a tumor for a slow release of chemotherapy.

The advantages, she noted, include greater safety for the practitioner than reconstituting and injecting a liquid solution into the tumor (cisplatin + sesame oil emulsion) and the possibility that fewer treatments are required (two compared to four treatments recommended for the liquid approach).

Cisplatin Bead

Placing bioabsorbable beads of the chemotherapeutic agent cisplatin in a tumor allows for a slow release of chemotherapy.

The beads are 3 mm wide and contain 1.6 mg of cisplatin. Large tumors (more than 1.5 cm wide) are surgically removed (debulked) before bead placement. Beads are placed in the incision at 1.5-cm intervals in most tumors, and at 2.5-3-cm intervals for tumors around the eye. Hewes prefers bioabsorbable sutures when closing the wound to avoid skin disruption with suture removal.

Horses are treated every 30 days until the tumor does not regrow; most horses in this study received two treatments. Any wound drainage is cleaned by a veterinarian wearing chemotherapy gloves to minimize exposure to cisplatin, and materials are disposed of in biohazard containers.

At the Marion duPont Scott Equine Medical Center in Leesburg, Va., 40 of 48 horses (83%) treated with this approach were relapse-free two years later. Hewes reported the following success rates from an article published in the Nov. 15, 2006, issue of the Journal of the American Veterinary Medical Association:

  • 91% (20/22) of cases with spindle cell tumors (sarcoids and fibrosarcomas) were relapse-free after two years. Three cases with regrowth at one, two, and three years resolved after one additional treatment.
  • Squamous cell carcinomas had the greatest tendency to recur (60% success rate), likely due to the duration of these cases and the increased metastatic (spreading) potential of this tumor type.
  • 93% (13/14) of melanoma cases were relapse-free after two years, including all affected gray horses. The one failure was a bay horse with malignant melanoma.
  • The sole cases of basal cell sarcoma and adenocarcinoma were relapse-free after two years.
  • One horse with lymphosarcoma showed metastasis after nine months.
  • Flat sarcoids don't respond well to this treatment; growth stops, but the tumor doesn't regress.

Complications included swelling, erythema (capillary congestion), wound drainage, subtle scarring, and a corneal ulcer requiring eye removal in one horse (following treatment of an upper eyelid tumor).

“Cisplatin beads are a simple and effective cutaneous (skin) neoplasia treatment," Hewes concluded. The beads are affordable for the average horse owner and are sold in three-packs.

About the Author

Christy M. West

Christy West has a BS in Equine Science from the University of Kentucky, and an MS in Agricultural Journalism from the University of Wisconsin-Madison.

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