Mesenchymal tumor-induced Fanconi syndrome: A novel classification of Fanconi syndrome

Rationale: Fanconi syndrome (FS) caused by mesenchymal tumors is rarely reported, and these tumors are usually small and difficult to detect. However, if found and removed, the FS can be cured. Patient concerns: Five patients were included in this study, and their clinical features, treatments, and prognoses of tumor-induced FS were reviewed and summarized. Diagnoses: Mesenchymal tumor-induced FS was diagnosed based on laboratory, imaging, and pathological examinations. Interventions: We performed tumor resection surgery and administered a symptomatic treatment regimen that included neutral phosphorus solution, calcitriol, calcium, and potassium supplementation, and acidosis correction. Outcomes: Two patients were cured, while 3 other patients showed transient symptomatic improvement postoperatively but still required symptomatic treatment due to tumor recurrence. Lessons: Our case report and literature review demonstrate that mesenchymal tumors should be included in the spectrum of disorders associated with FS and that FS may represent end-stage tumor-induced osteomalacia (TIO) in certain individuals. The diagnosis of FS requires consideration of tumor-induced causes, with early detection and complete resection being crucial for a cure.