Malignant Phosphaturic Mesenchymal Tumor, a Case Report
Poster #: 035
Session/Time: B
Author:
Madison Baldauf, BS
Mentor:
Shannon Lorimer, DO
Research Type: Case Report
Abstract
INTRODUCTION:
Phosphaturic mesenchymal tumors (PMTs) are rare neoplasms arising from bone or soft tissue. With less than 500 cases reported, approximately 35 are defined as malignant versus polyostotic. We present the case of a 44-year-old male with a pathologic fracture of the right femoral neck secondary to a malignant PMT with evidence of a metastatic lesion at the right proximal radius.
CASE INFORMATION:
The 44 year old male initially presented in October 2023 for right knee pain that progressed over nine months to include groin pain. There were no gross deformities, masses, swelling, or erythema. The patient, previously very active, had limited motion secondary to pain but was distally neurovascularly intact. Radiographs of the knee were unremarkable, however, hip films revealed a lucent lesion at the femoral neck with a pathologic fracture. Further imaging, biopsy, and a gene fusion panel were obtained, revealing a diagnosis consistent with PMT. Further PET-CT imaging revealed a secondary lesion at the right proximal radius, and several satellite lesions at the ribs. Biopsy at the radius was also consistent with PMT. The patient underwent surgical management with wide excision of the femoral tumor and proximal femoral replacement. Final pathology confirmed the diagnosis of malignant phosphaturic mesenchymal tumor. The patient has had an unremarkable postoperative course; currently he is scheduled for a proximal radius resection with subsequent radial head replacement and reconstruction with fibular-strut autograft to manage the secondary lesion.
DISCUSSION:
Phosphaturic Mesenchymal Tumors often present as tumor-induced-osteomalacia due to production of Fibroblast growth factor 23 (FGF-23). Diagnostic factors that may suggest malignancy are progressive increase in serum FGF-23, change in tumor size, and presence of multiple tumors, though multiplicity has been reported in benign cases as well. This benign multiplicity along with the vague symptoms such as generalized weakness make diagnosis very difficult. In this case, the patient's diagnosis was only delayed a few months after initial presentation, compared to an average delay of 5-7 years. The standard treatment of PMTs is complete surgical resection with wide margins. Based on previous case studies, resection alone has a 90% curative rate for benign and malignant PMTs. If the procedure is successful, serum values of FGF-23 and phosphate will normalize within one week and symptoms will resolve within 3-6 months. Post-operative phosphate and FGF-23 levels correlate with recurrence and should be used to monitor the patient.
CONCLUSION:
If a malignant or benign PMT is suspected, an extensive history and physical along with whole-body PET-CT is essential for making a diagnosis. A gene fusion panel should also be considered as approximately 42% of phosphaturic mesenchymal tumors harbor a fibronectin 1-fibroblast growth factor receptor 1 (FN1-FGFR1) fusion. This may, in the future, be an avenue for targeted therapy. Continued documentation of these rare cases is vital in order to understand the behavior and optimal management of malignant PMTs.
Phosphaturic mesenchymal tumors (PMTs) are rare neoplasms arising from bone or soft tissue. With less than 500 cases reported, approximately 35 are defined as malignant versus polyostotic. We present the case of a 44-year-old male with a pathologic fracture of the right femoral neck secondary to a malignant PMT with evidence of a metastatic lesion at the right proximal radius.
CASE INFORMATION:
The 44 year old male initially presented in October 2023 for right knee pain that progressed over nine months to include groin pain. There were no gross deformities, masses, swelling, or erythema. The patient, previously very active, had limited motion secondary to pain but was distally neurovascularly intact. Radiographs of the knee were unremarkable, however, hip films revealed a lucent lesion at the femoral neck with a pathologic fracture. Further imaging, biopsy, and a gene fusion panel were obtained, revealing a diagnosis consistent with PMT. Further PET-CT imaging revealed a secondary lesion at the right proximal radius, and several satellite lesions at the ribs. Biopsy at the radius was also consistent with PMT. The patient underwent surgical management with wide excision of the femoral tumor and proximal femoral replacement. Final pathology confirmed the diagnosis of malignant phosphaturic mesenchymal tumor. The patient has had an unremarkable postoperative course; currently he is scheduled for a proximal radius resection with subsequent radial head replacement and reconstruction with fibular-strut autograft to manage the secondary lesion.
DISCUSSION:
Phosphaturic Mesenchymal Tumors often present as tumor-induced-osteomalacia due to production of Fibroblast growth factor 23 (FGF-23). Diagnostic factors that may suggest malignancy are progressive increase in serum FGF-23, change in tumor size, and presence of multiple tumors, though multiplicity has been reported in benign cases as well. This benign multiplicity along with the vague symptoms such as generalized weakness make diagnosis very difficult. In this case, the patient's diagnosis was only delayed a few months after initial presentation, compared to an average delay of 5-7 years. The standard treatment of PMTs is complete surgical resection with wide margins. Based on previous case studies, resection alone has a 90% curative rate for benign and malignant PMTs. If the procedure is successful, serum values of FGF-23 and phosphate will normalize within one week and symptoms will resolve within 3-6 months. Post-operative phosphate and FGF-23 levels correlate with recurrence and should be used to monitor the patient.
CONCLUSION:
If a malignant or benign PMT is suspected, an extensive history and physical along with whole-body PET-CT is essential for making a diagnosis. A gene fusion panel should also be considered as approximately 42% of phosphaturic mesenchymal tumors harbor a fibronectin 1-fibroblast growth factor receptor 1 (FN1-FGFR1) fusion. This may, in the future, be an avenue for targeted therapy. Continued documentation of these rare cases is vital in order to understand the behavior and optimal management of malignant PMTs.