Cutaneous tumors are frequent in equidae. Sarcoids represent more than 50% of those tumors. Available treatments of equine cutaneous tumors include invasive techniques like surgery, cryosurgery or laser photovaporization and conservative techniques like brachytherapy, immunotherapy (BCG), intratumoral chemotherapy with cisplatin. However, there is no universal treatment especially against sarcoids. Surgical treatment leads to frequent relapses. BCG has an interest only on periocular sarcoids and could be life-threatening.
One of the most efficient treatments is intratumoral chemotherapy with cisplatin which combines easy use, low cost and high response rate (up to 96% on sarcoids and 88% on SCC) with a broad spectrum on the more prevalent equine skin neoplasms. Nevertheless, the main disadvantage is the poor diffusion of the hydrophilic drug into tumor cells. Cisplatin is therefore mixed with sesame oil in order to increase its tissue retention. However, some technical difficulties inherent to emulsion preparation or intratumoral injection may lead to cisplatin leakage and subsequently to a decrease of effectiveness.More recently the implantation of cisplatin-containing biodegradable beads has been demonstrated to be safe and effective for treating cutaneous neoplasms in horses. Both techniques are aimed at increasing cisplatin remanence at injection or implantation site
It has been shown that in vitro electropermeabilization of cells potentiates cytotoxicity of bleomycin by several hundred times and cytotoxicity of cisplatin up to 70 times. In vivo, electropermeabilization of cells potentiates antitumor effectiveness of cisplatin by a factor 20. This method, called electrochemotherapy (ECT), introduced in the 90's, has already been successfully applied to mice and rats for a large variety of tumors. Clinical trials have been performed in humans including small nodes of head and neck SCC, melanoma, basal cell carcinoma and adenocarcinoma. To date, very few data are available on domestic animals.
Increasing cisplatin concentration in sarcoids and other equine tumors by using ECT would therefore enhance the cytotoxic effect, thereby increasing treatment effectiveness.
Materials and Methods
All animals were treated under short term general anesthesia with intravenous agents. The tumor site was surgically prepared.
Cisplatin (Sigma-Aldrich laboratory, St-Quentin-Fallavier, France) was dissolved in phosphate buffer saline to obtain 1mg/mL solution. It was then administered with automatic or insulin syringes by injections (0.2-0.3 mL 6mm apart in the 3 dimensions) into the tumor mass and 1 cm of apparently healthy margin to reach a concentration of approximately 1 mg/cm3 of target tissue.
The generator was an electropulsator PS15 (Jouan, St Herblaine, France), which produced square waves electric pulses. Electric pulses were delivered using two stainless steel flat parallel electrodes (9 mm wide, 2 mm thick, 9 mm apart). Electric field intensity (E=U/d in V/cm) was taken as the ratio of voltage (U in Volts) on the distance between the electrodes (d in cm). The electric pulses were checked by an oscilloscope (Metrix, Annecy, France).
Within 5 minutes after cisplatin injection, the electrodes were put into contact with the skin on the tumor surface and the margins. The contact was ensured by application of an ultrasonic gel. Two runs of 8 electric pulses (duration 100 μs with 1300 V/cm electric field intensity which corresponds to a current voltage of 1170 V) were delivered at a frequency of 1 Hz in two orthogonal directions per site. When the tumor diameter exceeded 9 mm the procedure was repeated in order to cover the entire tumor surface and 1.5 cm of cutaneous margin.
When ECT was used in combination with surgery, the first ECT session was performed either at the time of surgery or 2-3 weeks post-operatively after wound healing completion.
Assessment of Tolerance
Animals were hospitalized for a minimum of two days. Blood hematology and biochemistry analyses were performed before each ECT session. Adverse effects were carefully monitored during and following treatment to the end hospitalization period.
Assessment of Therapeutic Efficacy
Tumors were staged by use of a modified tumor/node/metastasis (TNM) classification system according to their maximum diameter (T category: <2cm =T1; [2-5cm] =T2; [5-10cm] =T3; >10cm =T4).
The number of session was then adjusted to the tumor response observed: ECT treatment was repeated every 2 weeks until obtaining a sufficient response with a rest month after the first 4 sessions.
According to the WHO's guidelines, tumor response to ECT was considered as complete when there was no palpable or measurable tumor detected (CR)--partial when it showed greater than 50% decrease in tumor volume (PR)--no response in case of decrease of 50% or less in tumor volume or growth (NOR). The objective responses (OR) designates the compilation of complete and partial responses. Response per animal was the worst response on the per tumor basis.
Follow-up After Treatment
The two first control visits were done one and 6 months after the last ECT session. Tumor response was assessed at these occasions and further ECT sessions could be performed if necessary (in the case of incomplete treatment or partial response). The follow-up time is the observation time elapsed since the last ECT session. A third control visit was wished 12 months after the last ECT session in order to confirm a long-term response. Afterwards annual information's were collected by telephone with the referring veterinarians or directly with the owners and digital photographs were collected via internet mail.
Animals and Tumor Characteristics
57 equidae with cutaneous tumors presented at the Equine Teaching Hospital of Toulouse Veterinary School between October 1999 and December 2004 were included in the study. The 57 animals showed a total of 295 tumors whose 248 were treated by ECT.
Histological diagnosis showed 233 sarcoids of all forms and localizations (52 cases), 10 neurofibrosarcoma (3 cases), 1SCC (1 case) and 4 anaplastic sarcoma (1 case). Among the 233 sarcoids, 20 flats or occults, 93 verrucous, 78 nodular or fibroblastic and 42 mixed forms were treated by ECT.
Tumor stages included T1 (N=67), T2 (N=117), T3 (N=43) and T4 (N=21) before ECT 102 tumors were treated by ECT in combination with surgery (28 peri-operatively and 74 post-operatively).
All animals tolerated the treatment well. Muscular contractions were observed in response to each electric pulse. They were mostly limited to the skin muscles in the treated area. Local edema was the most frequent side-effect. It appeared within 24-48 hours after ECT and persisted one to 5 days. It was more marked in thin skin regions (facial or genital). These reactions were prevented by systematic NSAIDs premedication (phenylbutazone 2 mg/kg BID or flunixin meglumine 1.1 mg/kg SID). Esthetic and functional results were satisfactory with minimal healing contraction. There were no depilation and no change in hair color. When ECT was associated with surgery either perioperatively or postoperatively, it did not delay wound healing.
No systemic toxicity was noticed even in case of numerous treatments: 13 sessions (1 case). No effect was noticed on the reproductive function of 12 mares and 7 stallions treated by ECT.
A total of 248 tumors from 57 animals were treated. Five cases were withdrawn from the study upon owners' request after one to 5 sessions in spite of objective responses (41 tumors). Treatment was completed for 52 of the 57 animals and 207 of the 248 tumors.
On a per tumor basis and after one course of treatment (mean ECT sessions: 2.6 ± 1.1; range: 1-7), OR was 97.1%, CR was 92.8%, PR was 4.3% and NOR was 2.9%. 11 horses showing either PR (8) or limited regrowth (3) due to incomplete treatment (only 2 or 3 ECT sessions) were retreated upon owner's request 1 to 11 months later (mean 3.7 ± 2 months) through 1 to 5 additional sessions leading to a CR in all cases.
After this second course of treatment, final results on a per tumor basis were 98.6% OR with 98.1% CR, 0.5% PR and 1.4% NOR after a mean of 2.7 ± 1.3 ECT sessions (range: 1-8) and 47.5 ± 17.9 months follow-up (range: 16-90).
Final results on a per animal basis were 98.1% OR with 96.2% CR, 1.9% PR and 1.9% NOR after a mean of 3.6 ± 2.1 ECT sessions and 47.5 ± 17.9 months follow-up (range: 16-90).
Electrical treatment in a conscious horse can induce panic reactions, even under heavy sedation and local or loco-regional anesthesia, due to electric pulse perception by the animal. Therefore, each ECT session was conducted under general anesthesia as it is the case for conventional chemotherapy with uncooperative animals or when tumors are located in unfavorable locations. Acute local reactions were frequent but minor and no systemic toxicity was noticed in the course of ECT treatment or later even in reproductive animals.
Final results after the second course of treatment were 98.6% OR and 98.1% CR after a mean follow-up time of 47.5 months.
These results in equidae confirmed the usefulness of ECT as new antitumor treatment previously enlightened by clinical trials in human and veterinary oncology.
As suggested in our preliminary reports, this study demonstrates the high efficiency of ECT with cisplatin in the treatment of equine sarcoids (98%CR). It has been also equally effective at all body locations. The satisfactory functional and esthetic results (minimal scar, no depigmentation, no permanent depilation) would suggest to consider ECT as a treatment of choice of sarcoids located in delicate areas in order to preserve integrity of healthy tissue and also when esthetic considerations prevail.
The other tumor types present in this study (SCC, anaplastic sarcoma, neurofibrosarcoma) were also sensitive to ECT with cisplatin but not in sufficient number to conclude about the influence of this factor on tumor response. Electropermeabilization is in theory applicable to all histological cell types and in this study the results were significantly independent from the evolutive type of sarcoids.
ECT is a local treatment which could be performed in the case of numerous lesions on the same animal but could be limited by the time of anesthesia. In that cases the more aggressive tumors (fibroblastic or mixed large sarcoids) were given the priority and less aggressive or smaller tumors were delayed for treatment. During the treatment period of the prioritized tumors, no antitumor effect was observed on the non treated tumors which were treated as well in the following weeks.
This study demonstrates that ECT with cisplatin by intralesional route is a safe and efficient method for treatment of equine cutaneous tumors. It was easy to perform and didn't require special skills or specific rooms. The investment for equipment which is available now on the market for clinical use is affordable and should be cost-effective in specialized equine structures.
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