Month: December 2016
An Excellent Review of Current Imaging and Positron Emission Tomography (PET) Scanning and Their Use in Managing Recurrent and Advanced Disease
This website initially posted a review of positron emission tomography (PET) scanning on March 9th, 2015.
More recently, the Prostate Cancer Research Institute (PCRI) November Insights contained an updated and very informative review of the latest PET imaging techniques for managing recurrent and advanced prostate cancer. Their major utilities, advantages and their limitations are discussed clearly. The review was written by Dr. Fabio Almeida, Medical Director of Phoenix Molecular Imaging in Arizona. Rather than summarize the entire readable review, I will merely mention the various sections herein and provide the following link to the entire review.
In the November article, conventional types of imaging such as ultrasound, CT scans and prostate MRI and their uses are discussed initially. A section describing detection of bone metastases using Technetium-99 and sodium fluoride PET/CT scans follows. Carbon-11 acetate (available at Phoenix Molecular Imaging, Arizona) and C-11 choline (available at the Mayo Clinic, MN) are lipid metabolism PET agents both of which are useful for detecting recurrent disease and PSA relapse. In both cases, detection rates were dependent upon PSA values and doubling times.
Axumin (18F-FACBC) is a fluorine-18 radiolabeled synthetic leucine amino acid was has been recently approved by the FDA for detection of recurrent cancer in men with rising PSA after previous surgery or radiation. Amino acids are absorbed into cancer cells because of the increased metabolic demands of the growing cancer. In cited studies, optimal detection rates were seen when PSA levels were above 1.78. Direct comparison with C-11 choline scans indicated better performance for Axumin. For additional information on Axumin, see the website blog dated May 30, 2016.
The prostate-specific membrane antigen (PSMA) is a transmembrane glycoprotein that occurs much more commonly in prostate cancer cells compared to benign prostate tissue. One of the PSMA agents under development is 68-gallium-PS-MA-11, which has demonstrated a higher diagnostic efficiency compared to C-11 choline. Detection rates were dependent on PSA values. For example, a 93% detection rate was observed when the PSA was over 2.0 but only 50% when the PSA was 0.2-0.5. There are limitations to PSMA-targeting agents. Not all prostate cancers exhibit PSMA overexpression. In one study, about 8% of prostate cancer patients did not show PSMA overexpression. Benign lesions and several other types of cancers may also exhibit increased PSMA expression. False positive celiac lymph nodes have frequently been noted in the upper abdomen and detection of small locally-recurrent lesions and lymph nodes in the lower pelvis is challenging.
There is still no perfect imaging methodology with 100% accuracy. However, PSMA-targeted agents are becoming the major focus of future attention and development. “Despite some limitations, PSMA-targeted imaging appears to provide high sensitivity and specificity and is likely to become part of the routine evaluation and management of men with prostate cancer in the near future.”
For an initial review of PET imaging, see this website post dated October 9th, 2012.