Percutaneous microwave ablation of an acetabular phosphaturic mesenchymal tumor causing tumor-induced osteomalacia: a case report

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome caused by phosphaturic mesenchymal tumors (PMTs) that secrete fibroblast growth factor-23 (FGF23). These tumors are often small and anatomically challenging to localize, and surgical resection may be unfeasible in deep or complex locations. We report a 48-year-old woman presenting with progressive bone pain, lower limb weakness, and severe hypophosphatemia. 68 Ga-DOTATATE PET/CT identified multiple DOTATATE-avid lesions, of which three were most prominent: left acetabulum (SUVmax 13.16), left femoral head (SUVmax 7.71), and right femur lesser trochanter (SUVmax 7.09). Biopsy of the acetabular lesion confirmed PMT with strong SSTR2 immunohistochemical positivity and a Ki-67 index of 2%. Given the complex acetabular anatomy precluding safe surgical resection, the patient underwent CT-guided microwave ablation (MWA) of the acetabular lesion alone, with pre-procedural planning based on 68 Ga-DOTATATE PET/CT. Notably, while only the acetabular tumor was ablated, post-treatment PET/CT demonstrated a marked reduction in SUVmax not only in the treated site (to 1.08) but also in the untreated lesions (femoral head: to 4.04; lesser trochanter: to 5.21). Serum phosphate normalized by day 13. Transient exacerbation of bone pain occurred during the first week after ablation, while a surge in bone turnover markers (P1NP and β-CrossLaps) peaked at 2.7 months; both resolved by 8.7 months with sustained biochemical improvement. This case suggests that MWA may be a feasible and potentially effective minimally invasive alternative in selected patients with acetabular PMTs for whom surgical resection is associated with substantial morbidity. Because untreated DOTATATE-avid lesions were not histologically confirmed and sustained biochemical remission followed ablation of the single proven tumor, not all such lesions should be assumed to be true PMT metastases; biopsy confirmation is essential before treating additional sites.