Prostate Diagnostic and Assessment Tests
By Michael Downey
1. Transrectal Ultrasound
Transrectal ultrasound creates an image of the organs in the pelvis, and the most common indication is for the evaluation of the prostate gland in men with elevated PSA levels, or with prostatic nodules on a digital rectal exam.28 Ultrasound clarifies the size of the prostate gland and aids in the distinction between benign prostate conditions and prostate cancer.28 This type of imaging can also be used to help guide a biopsy of the prostate.28
2. Color Doppler Ultrasound
Color Doppler ultrasound is a medical imaging technique that is used to provide visualization of blood flow, using computer processing to add color to the image to greatly clarify what is happening inside the body.29 An ultrasound transducer is used to beam sound into the area of interest, and it reads the returning sound. When the sound bounces off a moving target such as a blood vessel, the pitch changes as a result of the Doppler effect. The transducer can detect very subtle pitch changes, record them visually, and generate an image showing where blood is flowing, and in what direction. Because a simple grayscale image can be a bit difficult to read, the ultrasound machine assigns different color values, depending on whether blood is moving towards or away from the transducer. In addition to showing the direction of flow, the colors also vary in intensity depending on the velocity of the flow, allowing doctors to also see how quickly the blood is moving.28
A color Doppler ultrasound of a patient with a suspected tumor will reveal the precise areas where the velocity of blood flow is changing, mapping out the problem in full color.30 This type of imaging can map out the tumor’s blood supply to clarify exactly how far the growth has spread. 31 This can have an impact on what treatments are selected, and how surgery and other measures are approached. While color Doppler ultrasound can be done using a transducer on the outside of the body, it can also be used for transrectal procedures, in which the probe is inserted to get a better view.
3. MRI (Magnetic Resonance Imaging)
The MRI has been used for over 30 years for prostate cancer detection and evaluation.32 In contrast to ultrasound imaging, prostate MRI has superior soft tissue resolution.33 Magnetic fields are used to locate and characterize prostate cancer. To do so, radiologists use multi-parametric MRI, which includes four different types of MRI sequences.32 Currently, MRI is used to identify targets for prostate biopsy, and to make a surgical plan for men undergoing robotic prostatectomy. MRI imaging also helps surgeons decide whether to resect or spare the neurovascular bundle and assess surgical difficulty.32
4. (Nuclear) Bone Scan
Prostate cancer can cause “hot spots” to appear on a bone scan if the cancer has metastasized to the bone.34,35 A bone scan for cancer uses nuclear technology and involves administering a radioactive substance called a tracer to produce gamma radiation that can be picked up by a special camera.34 The tracer consists of radionuclides that bind to the bone and show up as dark or light spots. After the technician injects the tracer, it usually takes between one and four hours for the radioactive substance to move throughout the skeleton. During this time, patients will be asked to drink up to six glasses of water to flush any tracer material not absorbed by bone. Then, the patient must remain still on a padded table while a large camera passes over the body.
A dark spot, also called a cold spot, might indicate lack of absorption of the tracer.34 This may also indicate that cancer has spread to the bone from the prostate gland. A normal scan shows evenly distributed tracer throughout the body. Risks associated with a bone scan are considered low, with a very small level of radiation exposure.34 The radionuclides injected into the bloodstream are excreted through the urine and have a low risk of toxicity.34
5. Quantitative Computed Tomography (QCT)
Osteoporosis, or bone thinning, is associated with prostate cancer and can be a side effect of prostate cancer treatment.36 Quantitative computed tomography (QCT) is a highly sensitive test that is better able to determine bone density changes than common methods such as DEXA testing.37 Studies have shown that DEXA testing can often read degenerative changes involving bone and joint tissues and calcium deposits within blood vessels as bone density thus not suggesting osteoporosis when in fact bone loss is present.38-41 Quantitative computed tomography QCT is similar to other forms of computed tomography (CT). As with any CT scan, an X-ray tube and sensor rotate around the body area in a circular or spiral pattern, and a series of pictures are transmitted to a computer.42 The primary difference with QCT is the special analysis performed by special QCT software. While most computed tomography (CT) software produces a composite visual image to detect fractures or other symptoms in the scanned bone or soft tissue, QCT uses the data provided by the scanner to generate numerical values for the volume, mass, and density of bone.42 This allows QCT to distinguish between cortical bone, which lines the outside of the bones, and trabecular bone, the softer tissue that makes up the center of the bone.43 Trabecular bone is much more metabolically active than cortical bone—meaning, the two types of bone are replaced at different rates.43 As a result, these two bone types can show different rates of change in bone mineral density.
About half of US men diagnosed with prostate cancer are classified as low-risk by use of conventional measures such as Gleason Score (a form of tumor grading), the prostate-specific antigen test (PSA), and a physical exam.44 Nonetheless, nearly 90% of these low-risk patients will choose to undergo immediate aggressive treatment such as radical prostatectomy or radiation even though there is less than a 3% chance of deadly progression.44
A new test called Oncotype DX is now available to physicians and their patients. It measures the level of expression of 17 genes across four biological pathways to predict prostate cancer aggressiveness.44
Test results are reported as a Genomic Prostate Score (GPS) ranging from 0 to 100; this score is assessed along with other clinical factors to clarify a man’s risk prior to treatment intervention.44 This multi-gene test has been validated using the prostate needle biopsy sample taken before the prostate is removed, thereby providing the opportunity for low risk patients to avoid invasive treatments. According to the principle investigator of the validation study, individual biological information from the Oncotype DX prostate cancer test almost tripled the number of patients who can more confidently consider active surveillance and avoid unnecessary treatment and its potential side effects.44
The advantage of this test for those who choose the comprehensive surveillance program utilized by Life Extension members (which involves the use of several drugs, targeted nutrients, and adherence to healthy dietary patterns) is to provide greater assurance the right course of action is being followed.
For information about the Oncotype DX test, log on to www.genomichealth.com
Prolaris® is another genomic test developed to aid physicians in predicting prostate cancer aggressiveness in conjunction with clinical parameters such as Gleason score and PSA.45
Prolaris® measures prostate cancer tumor biology at the molecular level. By measuring and analyzing the level of expression of genes directly involved with cancer replication, Prolaris may be able to more accurately predict disease progression.45
Prolaris® is a tool designed to measure the aggressiveness of a patient’s cancers to better predict and stratify an individual’s relative risk of disease progression within ten years.45 It may enable physicians to better define a treatment/monitoring strategy for their patients.
Prolaris® claims to be significantly more prognostic than currently used variables and provides unique additional information that can be combined with other clinical factors in an attempt to make a more accurate prediction of a patient’s cancer aggressiveness and therefore disease progression.45
Prolaris® has been shown to predict clinical progression in four different clinical cohorts, in both pre and post-treatment scenarios.
In the treatment of prostate cancer, Prolaris® is prognostic at the point of diagnosis and in the post-surgery setting.45
At diagnosis, Prolaris® can help to identify patients with less aggressive cancer who may be candidates for active surveillance. In addition, Prolaris® can define patients who appear clinically low-risk but have a more aggressive disease that requires more aggressive treatment.
Prolaris® testing is also well suited for use in post-prostatectomy patients that have higher risk features after surgery to better estimate their risk of disease recurrence and therefore adjust the level of monitoring or add additional therapy.
For more information about Prolaris®, log on to www.myriad.com