Absorbable chemotherapeutic beads combat cancer in horses

Editor's Note: This article was updated on July 14, 2024.

Absorbable chemotherapeutic beads containing cisplatin have been helpful in resolving equine cutaneous tumors as a standalone treatment or following laser debulking of the tumor prior to bead implantation. In a study, 83% of enrolled patients were tumor free at a 2-year follow-up. This included 20 of 22 horses with sarcoid or spindle cell tumors, 6 of 10 with squamous cell carcinomas, 13 of 14 with melanomas, and 2 of 3 with other tumor types.¹ Over the past few years, absorbable cisplatin beads have been only intermittently available for treatment of incompletely excised tumors. Because of these issues, an absorbable chemotherapeutic bead containing carboplatin using the Kerrier bead mold set has been developed.²

Preparation

The absorbable carboplatin beads are composed of a sterile mix 4 mL of (10 mg/mL) carboplatin and 15 g of calcium sulfate powder available from the Kerrier bead mold mixture (Figure 1). Sterile nitrile gloves should be used to effectively block the chemotherapy from being absorbed while handling the compound from the onset of making the chemotherapeutic beads to inserting them. Masks, goggles, and gowns are also typically worn as additional safety precautions.

Figure 1. (A) Absorbable chemotherapeutic bead in mold drying. (B) Removing 3 mm and 5 mm beads from mold. (C) Double packaging beads for gas sterilization.

After sterilely mixing the carboplatin liquid and calcium sulfate powder in a sterile bowl, the mixture is pressed into the silicone bead mold. Care is taken to remove air bubbles and fill the 3-mm bead molds first. The beads are left in the bead mold overnight to dry. Once dry, the absorbable beads are removed from the mold, double-packaged, labeled, and gas-sterilized for later use.

Administration

Figure 2. Cryotherapy after debulking the tumor, prior to insertion of chemotherapeutic beads.

Horses with cutaneous tumors in our clinic are typically treated with excisional biopsies whenever possible. If there is a chance the excision was incomplete, we perform cryotherapy at the surgical site (Figure 2). Following cryotherapy, we change gloves and instrument packs to prevent recontamination of our surgical site. Once the surgical site has been treated with 3 freeze-thaw cycles, the tissues are lavaged with sterile saline or saline containing 1:100 dilution of betadine solution. All significant sources of hemorrhage are ligated with 2-0 polyglactin 910 absorbable suture (Vicryl; Ethicon).

The surgical site is embedded with cisplatin absorbable beads in a grid pattern, starting ventrally and working proximally. Starting ventrally helps prevent bleeding from obscuring the surgical site as you work proximally. Beads are extended to 1-cm margins of the tumor whenever possible. Fresh 15 scalpel blades are used to make each new stab incision. The subcutaneous space is widened with mosquito hemostats, and a bead is placed in the tissue bed. The stab incision can be closed with 2-0 poliglecaprone 25 (Monocryl; Ethicon) or tissue glue. Finally, the wound bed is closed with 2-0 polyglactin 910 absorbable suture in the depths in a cruciate pattern oversewn by a simple continuous pattern. The skin is closed with a cruciate pattern of 2-0 poliglecaprone 25.

If excisional biopsy is not possible because of anatomic location (this often occurs around eyes), a punch biopsy is performed, and absorbable chemotherapeutic beads are used as a standalone treatment. Absorbable chemotherapeutic beads are placed in a grid pattern throughout the mass, including 1-cm margins.

Post treatment

Figure 3. (A) Erosive rapidly expanding squamous cell carcinoma at day 0. (B) 5 days after treatment (C) 14 days after treatment (D) 2 months after treatment with absorbable Carboplatin beads.

Since June 2021, at least 18 cutaneous tumors in horses have been treated at Tennessee Equine Hospital in Thompson’s Station using absorbable cisplatin or carboplatin absorbable beads. As practitioners, we treated 12 squamous cell carcinomas, 4 sarcoid tumors, and 2 other masses. Fourteen of 18 tumors completely resolved with 1 or 2 reapplications. (Figure 3). The 4 tumors that did not respond were squamous cell carcinoma with evidence of progression for over 1 year. In 14 cases, absorbable chemotherapeutic beads were used in conjunction with surgical debulking or excision and cryotherapy. In 4 cases, only the absorbable chemotherapeutic bead was used.

In our internal study at Tennessee Equine Hospital, the resolution rate was 88% with absorbable chemotherapeutic beads. In smaller or erosive tumors, the absorbable chemotherapeutic bead may offer a stand-alone treatment option for areas in which surgical excision may be detrimental, like the medial canthus of the eye. Insertion of 3-mm beads appears safe and easy to perform. Based on other studies, the chemotherapy is eluted from the bead for a minimum of 3 weeks.^2-4 Practitioners should base repeat absorbable chemotherapeutic bead placement on response of the tumor.

Allison A. Stewart, DVM, MS, DACVS, is a board-certified equine surgeon at Tennessee Equine Hospital, based in West Thompson’s Station. She enjoys furthering her knowledge in equine surgery. Retrospective evaluation of her cases has helped contribute to this knowledge base. Where her findings have contributed to a change or advancement in a procedure, she has felt it important to present the information. She has done this in abstracts, publications, and speaking when she feels it is a relevant contribution to veterinary medicine and surgery.

References

1. Hewes CA, Sullins KE. Use of cisplatin-containing biodegradable beads for treatment of cutaneous neoplasia in Equidae: 59 cases (2000- 2004). J Am Vet Med Assoc. 2006;229(10):1617-1622. doi:10.2460/javma.229.10.1617
2. Worth DB, Risselada M, Cooper BR, Moore GE. Repeatability of in vitro carboplatin elution from carboplatin-impregnated calcium sulfate hemihydrate beads made in a clinic setting. Vet Surg. 2020;49(8):1609-1617. doi:10.1111/vsu.13511
3. Belda B, Ramos-Vara J, Messenger KM, Risselada M. Pharmacokinetic and safety assessment of carboplatin-impregnated calcium sulfate hemihydrate beads in eight rats. Vet Surg. 2021;50(8):1650-1661. doi:10.1111/vsu.13712
4. Traverson M, Stewart CE, Papich MG. Evaluation of bioabsorbable calcium sulfate hemihydrate beads for local delivery of carboplatin. PLoS One. 2020;15(11):e0241718. doi:10.1371/journal.pone.0241718