Images of the treatment. Horses were treated in general anesthesia (A and B). Calcium chloride solution was injected in the sarcoid (C), followed by electroporation using needle electrodes (D). Photos: Frandsen et al.

A new treatment being used for cancer shows promise in treating sarcoids in horses, resulting in some cases in complete elimination.

Sarcoids are the most common equine skin tumors where the risk of recurrence after treatment is high, and better treatment options are warranted.

They are normally not lethal by themselves, but their size and distribution can severely compromise the use and value of the affected horse and lead to euthanasia

Stine Frandsen and her colleagues, writing in the journal Animals, have described their use of a procedure called calcium electroporation.

Calcium electroporation is a novel anti-cancer treatment in which calcium chloride solution is injected into the tumor, followed by brief high-voltage electric pulses (electroporation).

These pulses temporarily open the cell membranes and allow uptake of a high enough dose of calcium to kill the cancer cells.

The study, carried out in Denmark, centered on sarcoids in eight horses. The tumors were treated once or twice with calcium electroporation. The tumors were then monitored for 12 to 38 weeks.

Six of 27 sarcoids (22%) were completely eliminated through the treatment, and six further sarcoids (22%) decreased in size by more than 30%.

Another seven sarcoids showed limited changes in size (either getting a bit smaller or a bit bigger), while the remaining eight showed progressive disease, increasing in size by more than 20%.

The researchers were unable to find any relationship between the response and the location, type, or size of the sarcoids.

The study showed that calcium electroporation is a safe and feasible treatment for sarcoids, especially those considered inoperable.

Larger studies are needed to further investigate the effect of the treatment, they said.

The treatment was given under general anesthesia, but the horses were able to leave the clinic just a few hours after.

The researchers said the procedure was well tolerated by all horses, with no complications during anesthesia nor calcium electroporation treatment.

However, two horses developed a fever for 24 to 48 hours and were found to have an infection under the skin. These infections were successfully treated for five days with antibiotics.

The remaining horses were clinically unaffected except for local minor to moderate swelling of the treated area, but this subsided within a few days.

Discussing their findings, the study team said calcium electroporation proved to be a simple and inexpensive local tumor treatment. It was a technique that had already proven safe and efficient in human clinical trials.

They noted that a better response rate was seen in non-biopsied lesions, indicating that trauma induced by the treatment itself did not exacerbate the sarcoids. Indeed, in all four non-biopsied lesions in the study, complete elimination was achieved.

“It would be very interesting to investigate the response rate of calcium electroporation on sarcoids without concurrent biopsies in future studies.”

The researchers said that while the treatment method is feasible, it can be difficult to disperse calcium in the tough sarcoid tissue. They had therefore injected calcium in a grid pattern all over each sarcoid to ensure the presence of calcium throughout the tissue.

They pointed out that although electroporation equipment for veterinary use is reasonably priced, the cost of the treatment is higher than surgical removal.

“Furthermore, calcium electroporation may not be the first treatment choice for sarcoids based on these few cases since the response rate is slightly lower than after surgical removal.”

However, a  great advantage of calcium electroporation is that it can be used in areas where surgical removal is challenging, such as sarcoids on the eyelid.

In this study, sarcoids located around the eye of one horse that could not be surgically removed without removing the eye were treated with calcium electroporation with complete response.

“Thus, calcium electroporation may be a suitable treatment option for inoperable sarcoids.”

The full study team comprised Frandsen and Julie Gehl, both with Zealand University Hospital; Trine Tramm, with Aarhus University Hospital; and Martin Thoefner, with Hørsholm Hestepraksis.

Frandsen, S.K.; Gehl, J.; Tramm, T.; Thoefner, M.S. Calcium Electroporation of Equine Sarcoids. Animals 2020, 10, 517.

The study, published under a Creative Commons License, can be read here

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