Supplementary Material for: Multiple Bowen’s Disease in a Patient Treated with Ruxolitinib: A Case Report and Extended Review of the Literature

Introduction: Ruxolitinib, a Janus kinase (JAK) 1/2 inhibitor approved for the treatment of myelofibrosis and polycythemia vera, has been associated with an increased risk of non-melanoma skin cancer (NMSC). While squamous cell carcinoma (SCC), basal cell carcinoma (BCC), and keratoacanthomas (KA) are commonly reported, Bowen’s disease (BD), the in situ form of SCC, has been only rarely described. Case Presentation: We report the case of a 53-year-old woman with polycythemia vera, treated with ruxolitinib for over nine years. Six months after a dose escalation, she developed multiple erythematous, hyperkeratotic plaques on the trunk and limbs. Histopathological examination confirmed the diagnosis of BD. Over the years, she continued to develop new lesions approximately once per year. All lesions were managed successfully with cryotherapy or surgical excision, and no invasive SCC was observed. She has been under close dermatologic surveillance with full-body skin examinations every six months. Conclusion: This is the first fully documented case of eruptive, multiple Bowen’s disease associated with long-term ruxolitinib therapy. The distinctive chronic pattern, histologically confirmed and followed prospectively for nearly a decade, highlights a potentially underrecognized cutaneous adverse effect of JAK inhibition, warranting further research and awareness among prescribing clinicians.