What is prostate cancer?
To understand prostate cancer, it helps to know something about the prostate and nearby structures in the body.
About the prostate
The prostate is a gland found only in males. It is located in front of the rectum and below the urinary bladder. The size of the prostate varies with age. In younger men, it is about the size of a walnut, but it can be much larger in older men.
The prostate's job is to make some of the fluid that protects and nourishes sperm cells in semen, making the semen more liquid. Just behind the prostate are glands called seminal vesicles that make most of the fluid for semen. Theurethra, which is the tube that carries urine and semen out of the body through the penis, goes through the center of the prostate.
The prostate starts to develop before birth. It grows rapidly during puberty, fueled by male hormones (calledandrogens) in the body. The main androgen, testosterone, is made in the testicles. The enzyme 5-alpha reductaseconverts testosterone into dihydrotestosterone (DHT). DHT is the main hormone that signals the prostate to grow.
The prostate usually stays at about the same size or grows slowly in adults, as long as male hormones are present.
Benign prostatic hyperplasia
The inner part of the prostate (around the urethra) often keeps growing as men get older, which can lead to a common condition called benign prostatic hyperplasia (BPH). In BPH, the prostate tissue can press on the urethra, leading to problems passing urine.
BPH is not cancer and does not develop into cancer. But it can be a serious medical problem for some men. If it requires treatment, medicines can often be used to shrink the size of the prostate or to relax the muscles in it, which usually helps with urine flow. If medicines aren't helpful, some type of surgery, such as a transurethral resection of the prostate (TURP) may be needed. (See the "Surgery for prostate cancer" section for a description of this procedure.)
Prostate cancer
Several types of cells are found in the prostate, but almost all prostate cancers develop from the gland cells. Gland cells make the prostate fluid that is added to the semen. The medical term for a cancer that starts in gland cells isadenocarcinoma.
Other types of cancer can also start in the prostate gland, including sarcomas, small cell carcinomas, and transitional cell carcinomas. But these types of prostate cancer are so rare that if you have prostate cancer it is almost certain to be an adenocarcinoma. The rest of this document refers only to prostate adenocarcinoma.
Some prostate cancers can grow and spread quickly, but most grow slowly. In fact, autopsy studies show that many older men (and even some younger men) who died of other diseases also had prostate cancer that never affected them during their lives. In many cases neither they nor their doctors even knew they had it.
Possible pre-cancerous conditions of the prostate
Some doctors believe that prostate cancer starts out as a pre-cancerous condition, although this is not yet known for sure.
Prostatic intraepithelial neoplasia (PIN)
In this condition, there are changes in how the prostate gland cells look under the microscope, but the abnormal cells don't look like they are growing into other parts of the prostate (like cancer cells would). Based on how abnormal the patterns of cells look, they are classified as:
PIN begins to appear in the prostates of some men as early as their 20s. Almost half of all men have PIN by the time they reach 50. Many men begin to develop low-grade PIN at an early age but do not necessarily develop prostate cancer. The importance of low-grade PIN in relation to prostate cancer is still unclear. If a finding of low-grade PIN is reported on a prostate biopsy, the follow-up for patients is usually the same as if nothing abnormal was seen.
If high-grade PIN has been found on your prostate biopsy, there is about a 20% to 30% chance that you also have cancer in another area of your prostate. This is why doctors often watch men with high-grade PIN carefully and may advise them to have a repeat prostate biopsy, especially if the original biopsy did not take samples from all parts of the prostate.
Proliferative inflammatory atrophy (PIA)
This is another finding that may be noted on a prostate biopsy. In PIA, the prostate cells look smaller than normal, and there are signs of inflammation in the area. PIA is not cancer, but researchers believe that PIA may sometimes lead to high-grade PIN, or perhaps to prostate cancer directly.
What are the key statistics about prostate cancer?
Other than skin cancer, prostate cancer is the most common cancer in American men. The American Cancer Society’s estimates for prostate cancer in the United States for 2013 are:
About 1 man in 6 will be diagnosed with prostate cancer during his lifetime.
Prostate cancer occurs mainly in older men. About 6 cases in 10 are diagnosed in men aged 65 or older, and it is rare before age 40. The average age at the time of diagnosis is about 67.
Prostate cancer is the second leading cause of cancer death in American men, behind only lung cancer. About 1 man in 36 will die of prostate cancer.
Prostate cancer can be a serious disease, but most men diagnosed with prostate cancer do not die from it. In fact, more than 2.5 million men in the United States who have been diagnosed with prostate cancer at some point are still alive today.
What are the risk factors for prostate cancer?
A risk factor is anything that affects your chance of getting a disease such as cancer. Different cancers have different risk factors. Some risk factors, like smoking, can be changed. Others, like a person's age or family history, can't be changed.
But risk factors don't tell us everything. Many people with one or more risk factors never get cancer, while others who get cancer may have had few or no known risk factors.
We don't yet completely understand the causes of prostate cancer, but researchers have found several factors that might change the risk of getting it. For some of these factors, the link to prostate cancer risk is not yet clear.
Age
Prostate cancer is very rare in men younger than 40, but the chance of having prostate cancer rises rapidly after age 50. About 6 in 10 cases of prostate cancer are found in men over the age of 65.
Race/ethnicity
Prostate cancer occurs more often in African-American men and Jamaican men of African ancestry than in men of other races. African-American men are also more likely to be diagnosed at an advanced stage, and are more than twice as likely to die of prostate cancer as white men. Prostate cancer occurs less often in Asian-American and Hispanic/Latino men than in non-Hispanic whites. The reasons for these racial and ethnic differences are not clear.
Nationality
Prostate cancer is most common in North America, northwestern Europe, Australia, and on Caribbean islands. It is less common in Asia, Africa, Central America, and South America.
The reasons for this are not clear. More intensive screening in some developed countries probably accounts for at least part of this difference, but other factors such as lifestyle differences (diet, etc.) are likely to be important as well. For example, men of Asian descent living in the United States have a lower risk of prostate cancer than white Americans, but their risk is higher than that of men of similar backgrounds living in Asia.
Family history
Prostate cancer seems to run in some families, which suggests that in some cases there may be an inherited or genetic factor. Having a father or brother with prostate cancer more than doubles a man's risk of developing this disease. (The risk is higher for men who have a brother with the disease than for those with an affected father.) The risk is much higher for men with several affected relatives, particularly if their relatives were young at the time the cancer was found.
Genes
Scientists have found several inherited gene changes that seem to raise prostate cancer risk, but they probably account for only a small number of cases overall. Genetic testing for most of these gene changes is not yet available.
Some inherited gene changes raise the risk for more than one type of cancer. For example, inherited mutations of theBRCA1 or BRCA2 genes are the reason that breast and ovarian cancers are much more common in some families. Mutations in these genes may also increase prostate cancer risk in some men, but they account for a very small percentage of prostate cancer cases.
Recently, some common gene variations have been linked to a higher risk of prostate cancer. Studies to confirm this are needed to see if testing for the gene variants will be useful in predicting prostate cancer risk.
For more on some of the gene changes linked to prostate cancer, see “Do we know what causes prostate cancer?”
Diet
The exact role of diet in prostate cancer is not clear, but several factors have been studied.
Men who eat a lot of red meat or high-fat dairy products appear to have a slightly higher chance of getting prostate cancer. These men also tend to eat fewer fruits and vegetables. Doctors are not sure which of these factors is responsible for raising the risk.
Some studies have suggested that men who consume a lot of calcium (through food or supplements) may have a higher risk of developing prostate cancer. Dairy foods (which are often high in calcium) might also increase risk. Most studies have not found such a link with the levels of calcium found in the average diet, and it's important to note that calcium is known to have other important health benefits.
Obesity
Most studies have not found that being obese (very overweight) is linked with a higher risk of getting prostate cancer overall.
Some studies have found that obese men have a lower risk of getting a low-grade (less dangerous) form of the disease, but a higher risk of getting more aggressive prostate cancer. The reasons for this are not clear.
Some studies have also found that obese men may be at greater risk for having more advanced prostate cancer and of dying from prostate cancer, but not all studies have found this.
Smoking
Most studies have not found a link between smoking and the risk of developing prostate cancer. Some recent research has linked smoking to a possible small increase in the risk of death from prostate cancer, but this is a new finding that will need to be confirmed by other studies.
Workplace exposures
There is some evidence that firefighters are exposed to substances that may increase risk.
Inflammation of the prostate
Some studies have suggested that prostatitis (inflammation of the prostate gland) may be linked to an increased risk of prostate cancer, but other studies have not found such a link. Inflammation is often seen in samples of prostate tissue that also contain cancer. The link between the two is not yet clear, but this is an active area of research.
Sexually transmitted infections
Researchers have looked to see if sexually transmitted infections (like gonorrhea or chlamydia) might increase the risk of prostate cancer, possibly because they may lead to inflammation of the prostate. So far, studies have not agreed, and no firm conclusions have been reached.
Vasectomy
Some earlier studies had suggested that men who have had a vasectomy (minor surgery to make men infertile) – especially those younger than 35 at the time of the procedure – may have a slightly increased risk for prostate cancer. But most recent studies have not found any increased risk among men who have had this operation. Fear of an increased risk of prostate cancer should not be a reason to avoid a vasectomy.
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