The prostate is an exocrine gland of the male reproductive system, and exists directly under the bladder, in front of the rectum. An exocrine gland is one whose secretions end up outside the body e.g. prostate gland and sweat glands. It is approximately the size of a walnut. The urethra – a tube that goes from the bladder to the end of the penis and carries urine and semen out of the body – goes through the prostate.
There are thousands of tiny glands in the prostate – they all produce a fluid that forms part of the semen. This fluid also protects and nourishes the sperm. When a male has an orgasm the seminal-vesicles secrete a milky liquid in which the semen travels. The liquid is produced in the prostate gland, while the sperm is kept and produced in the testicles. When a male climaxes (has an orgasm) contractions force the prostate to secrete this fluid into the urethra and leave the body through the penis.
As the urethra goes through the prostate: the prostate gland is also involved in urine control (continence) with the use of prostate muscle fibers. These muscle fibers in the prostate contract and release, controlling the flow of urine flowing through the urethra.
The Prostate Produces Prostate-specific antigen (PSA)
The epithelial cells in the prostate gland produce a protein called PSA (prostate-specific antigen). The PSA helps keep the semen in its liquid state. Some of the PSA escapes into the bloodstream. We can measure a man’s PSA levels by checking his blood. If a man’s levels of PSA are high, it might be an indication of either prostate cancer or some kind of prostate condition.
It is a myth to think that a high blood-PSA level is harmful to you – it is not. High blood PSA levels are however an indication that something may be wrong in the prostate.
Male hormones affect the growth of the prostate, and also how much PSA the prostate produces. Medications aimed at altering male hormone levels may affect PSA blood levels. If male hormones are low during a male’s growth and during his adulthood, his prostate gland will not grow to full size.
In some older men the prostate may continue to grow, especially the part that is around the urethra. This can make it more difficult for the man to pass urine as the growing prostate gland may be causing the urethra to collapse. When the prostate gland becomes too big in this way, the condition is called Benign Prostatic Hyperplasia (BPH). BPH is not cancer, but must be treated.
In the vast majority of cases, the prostate cancer starts in the gland cells – this is called adenocarcinoma.
Prostate cancer is mostly a very slow progressing disease. In fact, many men die of old age, without ever knowing they had prostate cancer – it is only when an autopsy is done that doctors know it was there. Several studies have indicated that perhaps about 80% of all men in their eighties had prostate cancer when they died, but nobody knew, not even the doctor.
Experts say that prostate cancer starts with tiny alterations in the shape and size of the prostate gland cells – Prostatic intraepithelial neoplasia (PIN).
Doctors say that nearly 50% of all 50-year-old men have PIN. The cells are still in place – they do not seem to have moved elsewhere – but the changes can be seen under a microscope. Cancer cells would have moved into other parts of the prostate. Doctors describe these prostate gland cell changes as low-grade or high-grade; high grade is abnormal while low-grade is more-or-less normal.
Any patient who was found to have high-grade PIN after a prostate biopsy is at a significantly greater risk of having cancer cells in his prostate. Because of this, doctors will monitor him carefully and possibly carry out another biopsy later on.
Classification of prostate cancer
It is important to know the stage of the cancer, or how far it has spread. Knowing the cancer stage helps the doctor define prognosis – it also helps when selecting which therapies to use. The most common system today for determining this is the TNM (Tumor/Nodes/Metastases). This involves defining the size of the tumor, how many lymph nodes are involved, and whether there are any other metastases.
When defining with the TNM system, it is crucial to distinguish between cancers that are still restricted just to the prostate, and those that have spread elsewhere. Clinical T1 and T2 cancers are found only in the prostate, and nowhere else, while T3 and T4 have spread outside the prostate.
There are many ways to find out whether the cancer has spread. Computer tomography will check for spread inside the pelvis, bone scans will decide whether the cancer has spread to the bones, and endorectal coil magnetic resonance imaging will evaluate the prostatic capsule and the seminal vesicles.
The Gleason Score
A pathologist will look at the biopsy samples under a microscope. If cancer tissue is detected, the pathologist then grades the tumor. The Gleason System of grading goes from 2 to 10. The higher the number, the more abnormal the tissues are compared to normal prostate tissue.
Two numbers are added up to get a Gleason score:
- A number from 1 to 5 for the most common pattern observed under the microscope. This is the predominant grade and must be more than 51% of the sample.
- A number from 1 to 5 for the second most common pattern. This is the secondary grade and must make up more than 5% but less than 50% of the sample.
A Gleason score of 7 can have two meanings. Look at these two examples below:
- If the predominant grade is 3 and the secondary grade is 4, the Gleason score is 7.
- If the predominant grade is 4 and the secondary grade is 3, the Gleason score is also 7.
However, the first example, with a predominant score of 3, has a less aggressive cancer than the second example, with a predominant score of 4.
It is crucial that the tumor is graded properly, as this decides what treatments should be recommended.