Successful treatment of equine sarcoids with cisplatin electrochemotherapy: a retrospective study of 48 cases

Reasons for performing study: Sarcoids are the commonest form of equine skin tumour. Several therapeutic measures have been described but none is considered to be universally effective. Electrochemotherapy (ECT) is a new anticancer therapy that utilises electrical field pulses to induce increased cell membrane permeability to antitumour hydrophilic drugs, such as cisplatin. The increased intracellular concentration of the drugs has a significant therapeutic benefit. The procedure has not been previously reported in a large number of horses. Objective: To validate ECT as a novel alternative treatment for equine sarcoids. Methods: A retrospective study evaluating the efficacy of cisplatin ECT in the treatment of equine sarcoids was performed. Electrochemotherapy treatments were applied under general anaesthesia at 2 week intervals with or without prior excision or debulking. Electric pulses were directly applied to the lesions following intra‐tumoural injections of an aqueous solution of cisplatin. Results: One‐hundred‐and‐ninety‐four sarcoids on 34 horses, 2 ponies, 11 donkeys and one mule were treated with ECT. The 4 year nonrecurrence rate was 97.9% for animals (47/48) and 99.5% (193/194) for tumours. When ECT was used as a single treatment, a significant influence of tumour size (ρ= 0.55) on the number of treatments required for cure was shown. When prior surgery was performed, there was a significant influence (P<0.001) of the excision quality (complete or incomplete) and the healing mode (closed or open wound) on the number of treatments. The most common adverse effect was a slight oedematous reaction for lesions located on thin skin regions. Conclusion and clinical relevance: Results demonstrate that ECT, with or without concurrent tumour debulking, is an effective alternative for treatment of equine sarcoids.     

Molecular approaches to equine sarcoids

Sarcoids are the most commonly diagnosed skin tumours in equines. Bovine papillomaviruses (BPVs) are the primary causative agent of sarcoids. There has been intensive research to discover the molecular mechanisms that may contribute to the aetiopathogenesis of this disease and tumour suppressors and proto-oncogenes known to play a role in human neoplastic conditions have been investigated in equine sarcoids. Current approaches include the identification of gene expression profiles, characterising sarcoid and normal skin tissues, and an assessment of epigenetic alterations such as microRNA differential expression and DNA methylation status. This review focuses on selected groups of genes that contribute to the molecular mechanisms of sarcoid formation. These genes have the potential to complement current clinical examinations of equine sarcoid disease in diagnosis, prognosis, therapeutic response and screening.     

Sequences of papillomavirus DNA in equine sarcoids

DNA was extracted from 14 equine sarcoids, electrophoresed and hybridised with a radioactively labelled probe of bovine papillomavirus type I (BPV 1) DNA under conditions of low stringency. Twelve sarcoids contained sequences of DNA that hybridised with the probe and that comigrated with BPV 2 DNA. The viral DNAs in four of these sarcoids differed from BPV 1 and BPV 2 DNA on restriction endonuclease analysis. One of four cell lines derived from sarcoids also contained BPV 1 related DNA. The results confirm the frequent presence in equine sarcoids of unintegrated papillomaviral DNA and suggest a role for papillomavirus infection in this disease.     

The efficacy of intratumoural 5-fluorouracil for the treatment of equine sarcoids

OBJECTIVE: To document the efficacy of intratumoural injections of 5-fluorouracil for the treatment of equine sarcoids. DESIGN: A prospective study that included 13 horses and one donkey. PROCEDURE: Sarcoids were confirmed by histological examination and treated with intratumoural 5-fluorouracil every 2 weeks. If the sarcoids did not resolve after seven treatments, treatment was considered a failure. All cases were re-examined 6 months after treatment commenced and owners were telephoned 3 years after commencement of treatment to report on tumour recurrence. Outcome comparisons were performed to determine the effect of previous treatment, tumour size and tumour location on sarcoid resolution. The efficacy of intratumoural 5-fluorouracil was compared with other previously documented treatments of equine sarcoids. RESULTS: Sarcoids smaller than 13.5 cm3 were significantly (P = 0.032) more likely to resolve with treatment than larger sarcoids. Sarcoids that were not responsive to previous therapies were significantly (P = 0.007) more likely to recur after 3 years than sarcoids that had not been treated prior to this study. In this study, there were similar rates of resolution in cases with mutiple tumours (66.6%) when compared to cases with single tumours (60%). The numbers in this study were too small to properly evaluate the effect of tumour location on the success of treatment. Intratumoural 5-fluorouracil appeared to have resolved sarcoids in 9 of 13 cases (61.5%) as determined by follow up conversation with the owners 3 years after the initial treatment. CONCLUSION: The use of intratumoural 5-fluorouracil compares favourably with other treatment modalities for sarcoids, with a long term successful resolution rate of 61.5%. Owners should be warned that resistant sarcoids and sarcoids larger than 13.5 cm3 have a poorer prognosis for resolution and more aggressive therapeutic options should be considered.     

Management of equine sarcoids: 1975-93

Treatment options for equine sarcoids are briefly reviewed and the results of a retrospective study of 63 cases of equine sarcoid (66 lesions) treated by clinicians from the Rural Veterinary Centre, Camden, Australia from 1975 to 1993 presented. Five different treatments were employed in the management of these 66 lesions, including surgical excision alone or in combination with cryotherapy, radiotherapy, immunotherapy and tumour transfer to a subcutaneous site on the neck. The majority of cases were treated with surgical excision alone (18/66), excision followed by cryotherapy (31/66) and immunotherapy (16/66), with success rates of 28%, 42% and 81% respectively. Success was defined as no sign of recurrence of the lesion at the time of follow-up, at least 6 months later.     

Evaluation of excision, cryosurgery and local BCG vaccination for the treatment of equine sarcoids.

Ninety-five horses with sarcoids were subjected to three types of treatment: surgical excision (conventional or carbon dioxide laser), cryotherapy or local BCG vaccination. The type of treatment was selected on the basis of the size, location and clinical appearance of the tumours. The choice between conventional and laser excision was empirical. A successful outcome was obtained in 11 of 14 (79 per cent) of the horses treated by cryosurgery, 18 of 27 (67 per cent) treated by BCG vaccination, 18 of 22 (82 per cent) treated by conventional excision, and 20 of 28 (71 per cent) treated with a carbon dioxide laser. For both excision methods, rigorous measures were taken to avoid autoinoculation and to ensure a wide margin of normal skin. The probability of local recurrence after excision was significantly higher for large sarcoids and sarcoids which had previously failed to respond to treatment. In 10 of the 31 horses with remaining sarcoids, some or all of the untreated sarcoids were observed to regress spontaneously.     

Efficacy of imiquimod 5% cream in the treatment of equine sarcoids: a pilot study

Imiquimod is an immune response modifier with potent antiviral and antitumour activity. The objective of this pilot study was to evaluate the efficacy of an imiquimod 5% cream (Aldaratrade mark: 3M, Saint Paul, MN, USA) as a topical treatment for equine sarcoids. Fifteen horses with a total of 19 tumours were enrolled, including mixed (7), fibroblastic (5), flat (3), verrucous (2), and nodular (2) types. Baseline data included history, physical examination, tumour location, measurement and digital photography. Imiquimod was applied by the owners three times a week until complete resolution of the tumour or 32 weeks, whichever occurred first. Tumours were measured and photographed every 4 weeks. Treatment efficacy was defined as 75% or greater reduction of tumour size by the end of the trial. Four sarcoids were withdrawn from the study. Twelve of the remaining 15 tumours (80%) showed more than 75% reduction in size and nine (60%) totally resolved between 8 and 32 weeks. The most common adverse effects of exudation, erythema, erosions, depigmentation and alopecia were limited to the tumour and adjacent areas. The results suggest that topical imiquimod is a therapeutic option for the treatment of equine sarcoids, although more detailed studies are required to corroborate these initial findings.     

Glycolysis inhibition improves photodynamic therapy response rates for equine sarcoids

Photodynamic therapy (PDT) holds great promise in treating veterinary and human dermatological neoplasms, including equine sarcoids, but is currently hindered by the amount of photosensitiser and light that can be delivered to lesions thicker than around 2 mm, and by the intrinsic antioxidant defences of tumour cells. We have developed a new PDT technique that combines an efficient transdermal penetration enhancer solution, for topical delivery of 5‐aminolevulinic acid (ALA) photosensitiser, with acute topical post‐PDT application of the glycolysis inhibitor lonidamine. We show that the new PDT combination treatment selectively kills sarcoid cells in vitro, with repeated rounds of treatment increasing sarcoid sensitisation to PDT. In vivo, ALA PDT followed by 600 μM lonidamine substantially improves treatment outcomes for occult, verrucous, nodular and fibroblastic sarcoids after 1 month (93% treatment response in 27 sarcoids), compared with PDT using only ALA (14% treatment response in 7 sarcoids).     

Bovine papillomavirus infection in equine sarcoids and in bovine bladder cancers

Bovine papillomavirus (BPV) type 2 is involved in carcinogenesis of the urinary bladder in cattle, while BPV-1 is commonly associated with equine sarcoid tumours. In both cases the early viral proteins are expressed, but virion is not produced. Given the similarities in BPV biology between the tumours in cattle and horses, bovine bladder cancers and equine sarcoids were compared with respect to physical status, load of viral DNA and variability of the E5 open reading frame (ORF). Rolling circle amplification demonstrated that BPV-1 and BPV-2 genomes exist as double stranded, episomal, circular forms in the two tumours. Realtime quantitative PCR revealed that equine sarcoids contained higher viral DNA loads compared to bovine bladder cancers. The BPV-1 E5 ORF showed sequence variation but BPV-2 ORF did not. The presence of BPV-1 E5 variations or their absence in the BPV-2 E5 ORF does not appear to have an effect on viral DNA load in either tumour type.     

Clinical observations on the use of BCG cell wall fraction for treatment of periocular and other equine sarcoids

Clinical observations on the use of BCG cell wall fraction in oil for treating seven horses with periocular sarcoids and five horses with sarcoids in other regions are described. Therapy was successful when used for periocular or solitary and smaller sarcoids. For sarcoids previously treated with cryosurgery, therapy appeared to be less efficient. A horse with a sarcoid on the stifle developed a septic gonitis due to necrosis of the sarcoid tissue adjacent to the joint. Sarcoids of the axilla appeared to be more aggressive than sarcoids at other locations and did not respond favourably to this form of therapy.     

Whole genome scan identifies several chromosomal regions linked to equine sarcoids

Despite the evidence for a genetic predisposition to develop equine sarcoids (ES), no whole genome scan for ES has been performed to date. The objective of this explorative study was to identify chromosome regions associated with ES. The studied population was comprised of two half-sibling sire families, involving a total of 222 horses. Twenty-six of these horses were affected with ES. All horses had been previously genotyped with 315 microsatellite markers. Quantitative trait locus (QTL) signals were suggested where the F statistic exceeded chromosome-wide significance at P < 0.05. The QTL analyses revealed significant signals reaching P < 0.05 on equine chromosome (ECA) 20, 23 and 25, suggesting a polygenic character for this trait. The candidate regions identified on ECA 20, 23 and 25 include genes regulating virus replication and host immune response. Further investigation of the chromosome regions associated with ES and of genes potentially responsible for the development of ES could form the basis for early identification of susceptible animals, breeding selection or the development of new therapeutic targets.     

Phylogenetic analysis of bovine papillomavirus E5 detected in equine sarcoids in Poland

The aim of the study was to analyse a part of the sequence of the E5 gene of bovine papillomaviruses (BPV) associated with equine sarcoids in Polish horses. Samples of 40 skin lesions obtained from 29 horses were collected for molecular examination. The PCR amplicons of BPV DNA were detected in 38 specimens. After phylogenetic analysis 37 specimens were recognized as BPV-1 and one as BPV-2. Phylogenetic analysis has allowed the classification of the amplicons into two phylogenetic groups (A1,) and four separate isolates (2, 10, 16, 17).     

Pathomorphological and immunohistochemical study of selected markers of tumour cell proliferation in equine sarcoids

The purpose of the study was a pathomorphological and immunohistochemical analysis of tumour cells and connective tissue in equine sarcoids. Investigations were performed using histopathological, ultrastructural, immunohistochemical (PCNA, p53, cytokeratin, vimentin) and histochemical (Ag-NORs) methods. The study was conducted on 50 sarcoids originating from 36 horses and classified as occult, verrucous, fibroblastic and a mixed type of sarcoid based on their clinical appearance. Most of the tumours were located on the girth (30%), neck (24%), head (12%), and legs (12%). The average age of the horses at the first clinical examination was 5.7 years. The sarcoids occurred on the skin of mares (61%), geldings (31%) and stallions (8%), the predominant was Wielkopolska breed (41%) and mixed breeds with Wielkopolska breed (41%). The predominant colour was bay (80%). The data showed that the presence of characteristic, microscopic features was variable but it was not consistent enough to allow differentiation of the clinical types based on histopathology. PCNA expression was not characteristic for the clinical type of sarcoid but it appeared to be a useful tool for the determination of the biological activity of the tumour and the probability of its recurrence. No relationship was found between AgNORs and cell proliferation. The study demonstrated the presence of p53 positive cells in the epidermal and fibroblastic portions. Numerous p53-positive cells were observed in the sarcoids and tended to recurrence. The staining for cytokeratin and vimentin makes the diagnosis of tumour easier. The immunohistochemical studies of PCNA, and p53 are of great significance to the prognosis.