Bovine Papillomavirus DNA and S100 Profiles in Sarcoids and Other Cutaneous Spindle Cell Tumors in Horses.
Authors: Epperson E D, Castleman W L
Journal: Veterinary pathology
Summary
# Editorial Summary Distinguishing equine sarcoids from other dermal and subcutaneous spindle cell tumours, particularly peripheral nerve sheath tumours (PNSTs), relies heavily on histomorphological assessment, which can be unreliable; this study evaluated whether bovine papillomavirus (BPV) PCR testing and S100 immunohistochemistry could serve as reliable diagnostic adjuncts to differentiate these lesions. Researchers analysed 197 archived skin spindle cell tumours (including sarcoids, PNSTs, fibrosarcomas, and other soft tissue sarcomas) using both BPV DNA detection and S100 immunostaining to determine their diagnostic utility. BPV DNA presence was common across multiple tumour types—detected in 70% of sarcoids but also in 59% of PNSTs, 37% of fibrosarcomas, and 22% of other tumours—whilst S100 positivity was rare overall (6% of cases), appearing inconsistently across all tumour categories including both sarcoids and PNSTs. These findings significantly challenge the use of BPV and S100 as reliable standalone diagnostic markers, suggesting that many lesions historically classified as PNSTs based on morphology may represent soft tissue sarcomas with nerve sheath-like features rather than true nerve sheath tumours, and indicating that histopathological diagnosis remains essential alongside molecular testing rather than as a replacement for it. Practitioners should recognise that neither BPV positivity nor S100 negativity alone can confidently exclude sarcoid diagnosis, and that accurate tumour classification requires integration of morphological, molecular, and immunohistochemical data to guide appropriate management and prognostic counselling.
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Practical Takeaways
- •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
Key Findings
- •BPV DNA was present in 70% of sarcoids, 59% of PNSTs, 37% of fibrosarcomas, and 22% of other tumors, indicating BPV association extends beyond sarcoids to multiple soft tissue tumor types
- •S100 immunohistochemistry was positive in only 12 of 197 tumors (6%), including 3 sarcoids, 2 PNSTs, 5 fibrosarcomas, and 2 other sarcomas, making it a poor discriminator
- •41% of histomorphologically-classified PNSTs were BPV-negative and 94% were S100-negative, suggesting morphologic classification alone is unreliable for differentiating these tumor types