Catheterization to Locate Mesenchymal Tumors in Patients With Tumor-Induced Osteomalacia or Oncogenic Osteomalacia
Condition: Osteomalacia; Neoplasms
MeSH terms: Osteomalacia
Study type: Observational

Summary: 
      This study will use a procedure called selective venous catheterization in patients with
      tumor-induced osteomalacia (TIO) or oncogenic osteomalacia (OOM) to try to locate very small
      tumors that produce proteins called phosphatonins. Too much phosphatonin in the blood causes
      the kidneys to allow large amounts of phosphorus to be excreted in the urine, leading to low
      blood levels of phosphorus and, in turn, to osteomalacia (a condition of soft bones).
      Osteomalacia can cause bone fractures requiring many surgical procedures that can leave
      patients in pain. Patients may also feel weak and can lose height from massive bone loss.
      Selective venous catheterization is a way to measure the amount of phosphatonin in the blood
      and may be used as a way to locate phosphatonin-producing tumors that cannot be found using
      standard imaging techniques.

      Patients with TIO or OOM are screened under NIDR Protocol 01-D-0184 with a medical history,
      review of medical records and routine physical examination. Other procedures may include
      blood tests, urine tests, and imaging tests, such as x-rays, bone densitometry, bone scan,
      computed tomography (CT) and magnetic resonance imaging (MRI). This study will include mostly
      patients whose tumors were not able to be located through imaging procedures, but also a few
      patients whose tumors were located.

      All participants, regardless of whether or not their tumor was located, undergo selective
      venous catheterization. For this procedure, a radiologist inserts a catheter (thin flexible
      tube) into the body and uses fluoroscopy (a type of x-ray) to guide the tip of the catheter
      to different places in the body to collect small amounts of blood from the different areas.
      After the procedure, the patient lies flat for 2 hours and avoids moving his or her leg on
      the side where the catheter was placed.

      The blood is analyzed to measure the amount phosphatonin is in each sample, and the amounts
      are compared to the average amount of phosphatonin in the general blood circulation. If a
      higher level of phosphatonin is found in one area and the location of the tumor is unknown,
      the patient undergoes imaging in that area. If a tumor is found and it is in an area where it
      can be removed surgically, the patient is given the option to have the surgery. If the tumor
      is not found by imaging done after the first catheterization procedure, the patient has the
      option to have a second catheterization, taking samples of blood only from the area where the
      phosphatonin was found to be the highest during the sampling procedure.
    

Detailed description: 
      Phosphaturic mesenchymal tumors elaborate phosphate lowering factors (phosphatonins) which
      lead to tumor induced osteomalacia/osteogenic osteomalacia (TIO/OOM). Patients with TIO/OOM
      suffer years of significant morbidity and debilitation unless their tumors, which are
      notoriously difficult to locate, are removed.

      Selective venous catheterization has been used to localize hormonally active neoplasms by
      demonstrating a gradient in the concentration of the hormone of interest between the vessel
      immediately draining the tumor site and the peripheral circulation. The primary objective of
      this protocol is to evaluate the utility of combining selective venous catheterization with
      biochemical assays that identify phosphatonins in the serum as a way to identify phosphatonin
      gradients and thereby localize phosphaturic tumors.

      Our study population will consist of TIO/OOM patients with non-localized phosphaturic tumors
      as well as five patients whose lesions have been identified with some certainty by
      conventional imaging techniques. These individuals will undergo selective venous
      catheterization during which blood samples will be obtained and processed for the presence of
      phosphatonins. The primary endpoint will be met if a gradient indicating a possible tumor is
      found, focused clinical imaging in the appropriate anatomical sub-region identifies a lesion,
      and the lesion is confirmed to be a phosphaturic mesenchymal tumor upon surgical removal.
    

Keywords: Tumor Induced Osteomalacia; FGF-23; Phosphatonin; Hypophosphatemia; Oncogenic Osteomalacia; Phosphaturic Mesenchymal Tumor; TIO; Osteogenic Osteomalacia; OOM