What is Prostate specific membrane antigen (PSMA)?
Prostate specific membrane antigen (PSMA) is a kind of cell surface receptor. It is especially highly expressed in prostate cancer cells, particularly in its metastatic form – additionally expressed in various tissues like salivary glands, kidneys, liver, small intestine. Its membrane-bound feature makes PSMA an ideal target for drug delivery for both diagnostic and therapeutic purposes.
Thanks to newly developed ligands which bind to the extracellular part of PSMA so that we can scan living prostatic cells much better way.
Why use PSMA?
Prostate cancer is the most common type of cancer in men. As it is the case for most cancer types, it can metastasize to various tissues and organs.
Every cancer, incl. prostate cancer should be detected before it metastases. It is very important to detect the primary tumor and their metastases and treat properly if there are metastases.
In the treatment of prostate cancer, androgen deprivation therapy is applied to reduce testosterone levels since testosterone is the cause of prostate cancer cell growth and proliferation. But in some cases, the tumor cells are resistant to androgen deprivation therapy (mCRPC).
It is very important properly to monitor the treatment. Prostate cancer may occur again, and this recurrence may not be detected because technical limitations of medical imaging modalities (MRI, CT) or doctors may not be suspected of recurrence because the PSA level is low.
The treatment and follow up methods may not be adequate in some cases. Therefore, new methods are required to treat patients who do not respond to conventional therapy. If only PSA based screening or imaging is used, some recurrent cases may be missed.
According to recent studies, Gallium-68 (Ga-68) Lutetium-177 (Lu-177) agents are more sensitive for screening and more effective for treatment in mCRPC cases.
In this case, it is observed that theranostic agents can reduce the activity of prostate cancer in mCRPC and it is found that Gallium-68 (Ga-68) Lutetium-177 (Lu-177) PSMA are reliable to detect metastases and monitoring treatment.
Where is it used? In which medical applications?
PSMA-labeled Gallium(Ga)-68 PET scan is used for staging to detect primary tumors and its metastases with high accuracy. According to studies, Gallium-68 PSMA PET scan can detect very small metastases which are not detected by other scanning techniques like computed tomography (CT) and magnetic resonance imaging (MRI).
In addition, it is very successful – 88.1% sensitivity- in detecting recurrence in early periods.
Gallium-68 PSMA PET scan can also help us to evaluate the response of cancer to treatments.
With PSMA PET scanning, it is much easier to determine the stage of prostate cancer and whether it has spread to surrounding organs or tissues!
Who can benefit from use of PSMA?
- Patients with a Gleason score of 7 or more,
- In recurrent cases
When to use?
- before radiotherapy or
- 2 weeks after chemotherapy and hormone therapy or
- 6 weeks after radiotherapy
Does PSMA have any use in the treatment of prostate cancer? Is it safe to use PSMA?
In addition to diagnostic purpose, Lutetium (Lu)-177 PSMA can act as a therapeutic agent in metastatic castration-resistant prostate cancer (mCRPC). According to studies*, Lu-177 PSMA is very effective and safe in treatment; 28 months following Lu-177 PSMA therapy, the survival rate was 78.6%.
* Emmett L, Willowson K, Violet J et al. Lutetium 177 PSMA radionuclide therapy for men with prostate cancer: a review of the current