Equine Sarcoids: What the Research Says
Evidence from 21 peer-reviewed studies
What Professionals Should Know
- •FNA is a superior diagnostic tool to superficial swabs for confirming sarcoid diagnosis, especially for lesions with intact skin, improving diagnostic consistency in your clinical workup
- •Using FNA instead of swabs will reduce false negatives and the need for repeat sampling, allowing faster treatment decisions and better client communication
- •FNA can be incorporated into routine sarcoid diagnosis protocols to provide more reliable confirmation before committing to treatment, particularly for early-stage or non-ulcerated lesions
- •A novel sarcoid vaccine candidate has demonstrated safety and strong immunogenic response in a small equine trial, offering potential future protection against the most common equine skin tumor
- •The vaccine induced consistent antibody responses across all vaccinated horses with a simple two-dose protocol (3-week interval), suggesting feasible practical implementation if field efficacy is confirmed
- •While promising, this is early-stage work; practitioners should await larger field trials and regulatory approval before expecting this vaccine to become available for clinical use
- •Request histopathology with mitotic count assessment on all surgically excised sarcoids to identify high-risk cases (MC ≥20) requiring closer monitoring or alternative treatment approaches
- •Fibroblastic sarcoids carry substantially higher recurrence risk (75%) and may warrant more aggressive surgical margins, adjunctive therapies, or owner counselling about recurrence likelihood
- •For low-risk sarcoids (non-fibroblastic type, MC <20), standard surgical excision appears adequate with 82% success rate, though long-term monitoring remains important
- •BPV13 does not appear to be a significant cause of sarcoids in European horses and donkeys, so current vaccine strategies targeting BPV1/2 remain appropriate for these populations
- •Practitioners should be aware that BPV13 distribution may be geographically limited (Brazil) and not routinely screened for in European equids at this time
- •Larger multinational screening studies are needed to establish accurate BPV13 prevalence across Europe before revising diagnostic or preventive protocols
- •FAP-α immunohistochemistry may offer a new diagnostic tool for confirming sarcoid diagnosis in equine cases, potentially improving diagnostic accuracy
- •BPV appears uniformly present across different clinical sarcoid subtypes, suggesting viral activity alone does not determine clinical appearance—other factors likely influence phenotype
- •Verrucous sarcoids show a distinct subepithelial viral distribution pattern that may warrant consideration in histopathological assessment and tumor classification
- •PD-L1 checkpoint inhibitor immunotherapy is unlikely to be an effective treatment approach for equine sarcoids based on current evidence of minimal PD-L1 expression
- •Veterinarians should continue to rely on established sarcoid treatment modalities rather than anticipating checkpoint inhibitor therapies
- •Further investigation into alternative immune evasion mechanisms in equine sarcoids may be warranted to identify more promising immunotherapeutic targets
- •Understanding how BPV manipulates cellular autophagy may inform future targeted therapeutic approaches for treating equine sarcoids
- •Autophagy marker expression could potentially be used as a diagnostic or prognostic tool for equine sarcoid assessment
- •Recognition of viral strategies to evade immune response through autophagy modulation supports the need for mechanism-based rather than purely symptomatic treatment approaches
- •Equine sarcoids in your practice may be caused by BPV variants that have adapted for cross-species infection, suggesting the infection mechanism differs from bovine papillomavirus in cattle
- •Understanding that sarcoid-associated BPV variants exist globally (now documented in Japan) highlights the need for region-specific surveillance and potential implications for quarantine protocols when moving horses internationally
- •Genomic characterization of sarcoid lesions could potentially support diagnosis and treatment decisions, though clinical application remains to be determined
- •BPV PCR and S100 immunohistochemistry alone cannot reliably differentiate equine sarcoids from other spindle cell tumors; histomorphologic classification combined with molecular testing is needed for accurate diagnosis
- •When submitting skin tumors for pathology, expect that sarcoids and nerve sheath tumors may have overlapping molecular and immunologic profiles and require careful integrated interpretation
- •Many equine skin tumors carry BPV DNA regardless of traditional classification, so treatment decisions should rely on complete histopathologic evaluation rather than single diagnostic markers
- •PNL2 is a reliable immunohistochemical marker for confirming equine melanoma diagnosis with better specificity than conventional S100 staining
- •Melan A antibody should not be used for equine melanoma diagnosis as it does not cross-react with equine melanomas, despite effectiveness in human pathology
- •Pathologists should request PNL2 immunostaining when diagnosing suspected equine melanocytic tumors for improved diagnostic accuracy
- •Sarcoid development involves disruption of tumour suppressor genes similar to human papillomavirus-associated cancers, suggesting potential therapeutic targets
- •Understanding the molecular basis of BPV-associated transformation may inform future prevention or treatment strategies for equine sarcoids
- •Equine sarcoids harbour substantially more BPV-1 DNA than bovine bladder cancers harbour BPV-2, which may influence treatment approaches and viral shedding potential
- •The consistent lack of variation in BPV-2 E5 (unlike BPV-1) suggests different viral evolutionary pressures in cattle versus horses that may have implications for cross-species transmission risk
- •Understanding the episomal nature of BPV genomes in sarcoids supports investigation of therapies targeting viral DNA maintenance rather than integration
- •Hypericin-based photodynamic therapy shows promising early results for equine sarcoid treatment with substantial tumor volume reduction, though more clinical trials are needed before practice adoption
- •Treatment protocol involved four intratumoural injections followed by daily illumination over 25 days, suggesting this is a time-intensive procedure requiring commitment
- •As a non-invasive approach, this technique could offer an alternative to traditional surgical or other invasive sarcoid treatments, potentially reducing complications and recovery time
- •Early recognition and management of sarcoids is important as they are locally aggressive lesions that can interfere with tack fit and athletic performance
- •Treatment selection should be individualized based on sarcoid type, location, and available evidence, as no single approach works universally
- •Affected horses may experience reduced market value, so discuss realistic treatment expectations and prognosis with owners early in management
- •If sarcoid vaccines are developed for New Zealand horses, ensure they provide robust protection against BPV2, the causative agent in approximately 88% of cases
- •BPV1 and BPV2 co-infections occur in roughly 1 in 10 sarcoids, suggesting some horses may be exposed to multiple bovine papillomavirus types through cattle contact
- •About 10% of sarcoids lack detectable papillomavirus DNA, indicating either undetected PV types, integration patterns missed by current PCR methods, or alternative non-viral causes
- •Do not rely on clinical judgment alone for equine sarcoid diagnosis—even experienced clinicians misdiagnose ~17% of cases; always obtain histopathology for lesions where treatment is planned
- •High diagnostic confidence does not correlate with accuracy, particularly in less experienced practitioners; when uncertain, biopsy rather than treat empirically to avoid unnecessary morbidity
- •The high positive predictive value (88.4%) means if you think it's a sarcoid you're likely right, but the lower negative predictive value (72.0%) means a clinical 'not sarcoid' diagnosis is less reliable and should prompt biopsy if clinical doubt exists
- •Implementing a structured diagnostic protocol can significantly improve your accuracy in diagnosing equine sarcoids and reduce misdiagnosis rates, particularly valuable if you lack extensive experience with this condition
- •Use of a protocol-guided approach increases diagnostic confidence while simultaneously improving accuracy—allowing you to make more informed decisions about which lesions require biopsy confirmation
- •The DP can help identify diagnostically challenging cases and guide when specialist referral or tissue sampling is appropriate rather than relying on clinical impression alone
- •PDT represents a non-invasive alternative for managing equine sarcoids and other superficial neoplasias with minimal scarring and rapid tissue healing
- •The dual diagnostic and therapeutic capability of photosensitiser dyes could improve surgical planning by allowing better tumor visualization before treatment
- •PDT's mechanism of action through immune stimulation and vascular disruption offers advantages over traditional therapies, though further veterinary research is needed to establish optimal protocols
- •Equine sarcoids represent a failure of local cell-mediated immunity to clear BPV infection, unlike the spontaneous regression seen in cattle, explaining why equine sarcoids persist and recur frequently
- •The immunological deficiency in equine sarcoids involves both reduced pro-inflammatory T cell responses and altered regulatory T cell populations, which may inform future immunotherapeutic approaches
- •Understanding that equids lack effective anti-BPV immunity helps explain variable treatment outcomes and supports the need for novel therapeutic strategies beyond current surgical and topical management
- •Electrochemotherapy with cisplatin offers a new treatment option for equine sarcoids when conventional therapies have failed or are unsuitable.
- •The technique has demonstrated efficacy in a substantial case series and warrants consideration as part of the diagnostic and treatment toolkit for skin tumours in horses.
- •Practitioners should be aware that this technology requires specialized equipment and training, but may provide better outcomes than traditional approaches for this common condition.
- •Superficial swabs and scrapings are practical, non-invasive sampling methods for BPV detection in sarcoids, with scrapings showing slightly higher success rates (93%) than swabs (88%)
- •BPV DNA detection via PCR on superficial samples could help confirm sarcoid diagnosis without requiring tissue biopsy
- •The high specificity (100% in controls) suggests this PCR method is reliable for differentiating sarcoids from other skin lesions in horses
Key Research Findings
Fine-needle aspiration (FNA) detected BPV in 98% of sarcoid lesions compared to 70% with superficial swabs (P = 0.0001)
FNA detected BPV in 98% of non-ulcerated lesions versus 63% with swabs (P = 0.0001), demonstrating superior performance on intact epithelium
FNA demonstrated 23-52% higher sensitivity, negative predictive value, and accuracy compared to superficial swabbing across different lesion types
FNA reduces risk of false positives from superficial contamination and latent BPV detection while improving adequacy of sampling
A recombinant baculovirus vector vaccine expressing BPV1 L1 protein was safe with no clinically relevant adverse reactions observed in 10 vaccinated horses
All 10 vaccinated horses developed neutralizing antibody titers ranging from 40 to >1280 after two intramuscular doses at 3-week intervals
Control group horses (n=5) and pre-vaccination sera showed no detectable virus-neutralizing antibodies
Robust neutralizing antibody response indicates potential protective efficacy against equine sarcoids, pending field efficacy studies
Overall recurrence rate was 24% (12 of 49 cases) following surgical excision
Sarcoids with mitotic count ≥20 per 2.37 mm² had 80% recurrence rate versus 18% for those with mitotic count <20 (P=0.0051)
Fibroblastic clinical type showed 75% recurrence rate compared to 18% for other types (P<0.001)
Mitotic count ≥20 and fibroblastic type were significant independent predictors of recurrence on Cox regression analysis
BPV13 DNA was not detected in any of 135 tumor DNA samples from sarcoid-affected horses and donkeys across Austria, Northern Italy, and the UK
All positive, negative, and no-template PCR controls yielded expected results, confirming assay reliability
The study suggests low occurrence of BPV13 in tested European equids with sarcoid disease, contrasting with recent Brazilian findings
Evidence Base
Cross-sectional comparison of superficial swab and fine-needle aspiration: Improving the diagnostic workup of horses with sarcoids.
Gysens Lien, Martens Ann, Haspeslagh Maarten (2022) — Veterinary journal (London, England : 1997)
Safety and immunogenicity of a sarcoid vaccine in horses.
Jacob O, Hause B, Peters-Smith K et al. (2025) — Journal of equine veterinary science
Equine sarcoids: A clinicopathologic study of 49 cases, with mitotic count and clinical type predictive of recurrence.
Karalus Wilson, Subharat Supatsak, Orbell Geoff et al. (2024) — Veterinary pathology
Screening for bovine papillomavirus type 13 (BPV13) in a European population of sarcoid-bearing equids.
Jindra Christoph, Kamjunke Ann-Kristin, Jones Sarah et al. (2021) — Equine veterinary journal
Fibroblast-associated protein-α expression and BPV nucleic acid distribution in equine sarcoids.
Tura Giorgia, Savini Federica, Gallina Laura et al. (2021) — Veterinary pathology
Immunohistochemical Analysis of Programmed Death-Ligand 1 Expression in Equine Sarcoids.
Benvegnen Jennifer, De Breuyn Bettina, Gerber Vinzenz et al. (2021) — Journal of equine veterinary science
Beclin 1, LC3 and P62 Expression in Equine Sarcoids.
Martano Manuela, Altamura Gennaro, Power Karen et al. (2021) — Animals : an open access journal from MDPI
Genomic characterisation of bovine papillomavirus types 1 and 2 identified in equine sarcoids in Japan.
Yamashita-Kawanishi Nanako, Chambers James K, Uchida Kazuyuki et al. (2021) — Equine veterinary journal
Bovine Papillomavirus DNA and S100 Profiles in Sarcoids and Other Cutaneous Spindle Cell Tumors in Horses.
Epperson E D, Castleman W L (2017) — Veterinary pathology
Immunohistochemical expression of melanocytic antigen PNL2, Melan A, S100, and PGP 9.5 in equine melanocytic neoplasms.
Ramos-Vara J A, Frank C B, DuSold D et al. (2014) — Veterinary pathology
Molecular and epigenetic analysis of the fragile histidine triad tumour suppressor gene in equine sarcoids.
Strazzullo Maria, Corteggio Annunziata, Altamura Gennaro et al. (2012) — BMC veterinary research
Bovine papillomavirus infection in equine sarcoids and in bovine bladder cancers.
Yuan Zhengqiang, Gallagher Alice, Gault Elizabeth A et al. (2007) — Veterinary journal (London, England : 1997)
In vitro and in vivo evaluation of hypericin for photodynamic therapy of equine sarcoids.
Martens A, de Moor A, Waelkens E et al. (2000) — Veterinary journal (London, England : 1997)
Management of equine sarcoids.
Hollis Anna R (2023) — Veterinary journal (London, England : 1997)
Evidence from a Series of 104 Equine Sarcoids Suggests That Most Sarcoids in New Zealand Are Caused by Bovine Papillomavirus Type 2, although Both BPV1 and BPV2 DNA Are Detectable in around 10% of Sarcoids.
Munday John S, Orbell Geoff, Fairley Rob A et al. (2021) — Animals : an open access journal from MDPI
The clinical diagnosis of equine sarcoids - Part 1: Assessment of sensitivity and specificity using a multicentre case-based online examination.
Koch C, Martens A, Hainisch E K et al. (2018) — Veterinary journal (London, England : 1997)
The clinical diagnosis of equine sarcoids-Part 2: Assessment of case features typical of equine sarcoids and validation of a diagnostic protocol to guide equine clinicians in the diagnosis of equine sarcoids.
Haspeslagh M, Gerber V, Knottenbelt D C et al. (2018) — Veterinary journal (London, England : 1997)
Photodynamic therapy and diagnosis: Principles and comparative aspects.
Dobson Jane, de Queiroz Genilson Fernandes, Golding Jon P (2018) — Veterinary journal (London, England : 1997)
Quantitative analysis of infiltrating immune cells and bovine papillomavirus type 1 E2-positive cells in equine sarcoids.
Geisshüsler H, Marti E, Stoffel M H et al. (2016) — Veterinary journal (London, England : 1997)
Successful treatment of equine sarcoids with cisplatin electrochemotherapy: a retrospective study of 48 cases.
Tamzali Y, Borde L, Rols M P et al. (2012) — Equine veterinary journal