Presentations

Abstract

Introduction: Cancer is one of the leading causes of death worldwide, currently rated the first or second most common contributor to premature mortality in most countries. The global number of patients with cancer is expected to rise over the next 50 years, with some models predicting a doubling of incidence of all cancers combined by 2070 relative to 2020. Therefore, accurate diagnosis, staging, and restaging are essential for the optimal therapeutic management of cancer patients. Positron Emission Tomography (PET) continues to emerge as an imaging modality with reliable clinical value in the management of cancer patients. PET imaging utilizes radioactive molecules called radiotracers that can provide a higher level of detail of specific physiological processes over more conventional cross-sectional imaging. In many tumor types, the rate of glucose utilization is significantly enhanced compared to normal tissues. The altered metabolism of tumor cells can be detected by using radiotracers. Different types of tumors display varying affinity for different radiotracers; thus a range is available depending on the type of cancer being investigated. Facing the increasing worldwide prevalence of cancer, clinicians of all specialties should be familiar with commonly used radiotracers. The following is a literature review and educational symposium of three major PET radiotracers - FDG, PSMA, and Dotatate.

Main Body: A comprehensive literature review was conducted using PubMed. The review included articles reporting FDG, PSMA, and Dotatate, summarizing the mechanism of action, indications, pathologic distribution, and unique areas of activity for each radiotracer. FDG is the most commonly used radiotracer for oncologic indications. It has high sensitivity for a wide variety of tumors but is not tumor-specific. It is used in the following cancers: lung, lymphoma, head and neck tumors, breast, esophageal, colorectal, pancreatic, gynecological, GU, and melanoma. Prostate specific membrane antigen (PSMA) is specific to prostate cancer. It is a protein found in normal prostate tissue but significantly over expressed in prostate cancer tissue. PSMA expression can also be found in the salivary and lacrimal glands, nasopharynx and larynx, liver, spleen, bowel, the kidneys and the sympathetic ganglia. PSMA uptake is also found in other tumors including glioblastoma, thyroid, breast, lung, colon and renal carcinomas. PSMA uptake is also seen in benign tumors, e.g., hemangiomas, thyroid and adrenal adenomas, schwannomas and desmoid tumors. It is also seen in some reactive/inflammatory conditions and Paget's disease. Dotatate is used for the assessment of well-differentiated neuroendocrine tumors (NETs). Dotatate is a somatostatin analog. It is beneficial for molecular imaging of NETs as most types demonstrate high levels of somatostatin receptor expression. Normal tissues with high physiological uptake of Dotatate include spleen, kidneys, liver, pituitary gland, thyroid gland, and adrenals. High uptake is also seen in the pancreas uncinate process.

Conclusion: The increasing incidence of cancers of all types places growing importance on utilizing accurate methods for diagnosis and staging. PET-CT continues to emerge as a promising modality in the management of cancer patients. This presentation focused on a review of three commonly used radiotracers: FDG, PSMA, and Dotatate. FDG is the most commonly used radiotracer for oncologic indications. It functions as a marker of cellular metabolic activity and is sensitive for a wide variety of tumors, though not-tumor specific. PSMA and Dotatate function more as cellular markers and are more specific for prostate cancer and neuroendocrine tumors, respectively.