Oncology, bone metastases

Metastatic disease is the most common malignancy of the bone and the skeleton is one of the preferential sites for metastases of solid tumor. Osteotropic radiopharmaceuticals are bone seeking agents which target skeleton due to their osteoblastic activity. The most common in clinical use is Sodium-18 fluoride (Na18F). 18F-NaF PET/CT plays essential role in initial staging, detection of suspected metastases, suspected progression of osseous metastases or treatment monitoring in many types of cancer, such as prostate, breast and lung cancer. Additionally, the role18F-NaF PET/CT in the diagnostics of thyroid cancer, renal cell cancer, multiple myeloma and metastatic primary bone tumors is discussed. Specific oncotropic PET agents are tumor targeting compounds, such as Iodine-124 for metastatic thyroid cancer, and somatostatin analogs (Ga-68DOTA-octreotide/octreotate) for neuroendocrine neoplasms. These tracers disclose bone metastases in the malignancies. Multiple tracers for prostate cancer are presented with varying ability to target malignant skeletal disease. Hormone receptor imaging is presented, FES PET is a prime example to demonstrate estrogen receptor positive skeletal disease. Non-specific oncotropic Agents are important in the detection of skeletal metastases. Actually, the most common PET tracer, F-18 fluorodeoxyglucose (18F-FDG), plays an important role in the diagnosis of many malignancies. However, the differential diagnosis and sensitivity may sometimes cause problems which should be identified. F-18 (C-11) Choline is associated with lipid synthesis and more sensitive than conventional bone scintigraphy in the diagnosis of bone metastases of prostate cancer. On the contrary, fluorothymidine (18F-FLT) which targets DNA and cellular proliferation, is not sensitive at all the in the follow-up of skeletal metastases. This article provides an overview about the diagnostics of bone metastases. Additionally, practical pitfalls are presented as well as new ideas how to improve diagnostics, such as quantitation methods and double-tracer techniques.