The prostate is a walnut-sized gland located in front of the rectum and underneath the urinary bladder. It is found only in men. The prostate's job is to make some of the fluid that protects and nourishes sperm cells in semen. Just behind the prostate gland are the seminal vesicles that make most of the fluid for semen. The urethra, which is the tube that carries urine and semen out of the body through the penis, runs through the prostate.
The prostate starts to develop before birth and continues to grow until a man reaches adulthood. This growth is fueled by male hormones (called androgens) in the body. The main androgen, testosterone, is made in the testicles. The enzyme 5 alpha-reductase converts testosterone into dihydrotestosterone (DHT). DHT signals the prostate to grow. The prostate stays at adult size in adults as long as male hormones are present. In older men, the inner part of the prostate (around the urethra) often keeps growing, leading to a common condition called benign prostatic hyperplasia (BPH). In BPH, the prostate tissue can press on the urethra, leading to problems passing urine. Although BPH can be a serious medical problem, it is not cancer.
Prostate cancer
Several types of cells are found in the prostate, but over 99% of 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 is adenocarcinoma.
Other types of cancer can also start in the prostate gland, including sarcomas, small cell carcinomas, and transitional cell carcinomas. But because these other types of prostate cancer are so rare, 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 of them 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 these studies, 70% to 90% of the men had cancer in their prostate by age 80, but in many cases neither they nor their doctors even knew they had it.
Pre-cancerous conditions of the prostate
Many doctors believe that prostate cancer begins with a pre-cancerous condition called prostatic intraepithelial neoplasia (PIN). 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. 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). The cell changes are classified as either low-grade, meaning the patterns of prostate cells appear almost normal, or high-grade, meaning they look more abnormal.
If you have had high-grade PIN found on a 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 a repeat prostate biopsy, especially if the original biopsy did not take samples from all parts of the prostate.
Another finding that may be reported on a prostate biopsy is atypical small acinar proliferation (ASAP), which is sometimes just called atypia. In ASAP, the cells look like they might be cancerous when viewed under the microscope, but there are too few of them on the slide to be sure. If ASAP is found, there's about a 40% to 50% chance that cancer is also present in the prostate. This is why many doctors advise getting a repeat biopsy within a few months.
Another finding that may be reported on a prostate biopsy is proliferative inflammatory atrophy (PIA). In PIA, the cells look abnormal when viewed under the microscope. PIA is not cancer, but researchers believe that some PIA cells can turn into prostate cancer directly or by first changing into high-grade PIN.
What are the key statistics about prostate cancer?
Other than skin cancer, prostate cancer is the most common cancer in American men. The latest American Cancer Society estimates for prostate cancer in the United States are for 2010:
- About 217, 730 new cases of prostate cancer will be diagnosed
- About 32,050 men will die of prostate cancer
About 1 man in 6 will be diagnosed with prostate cancer during his lifetime. More than 2 million men in the United States who have been diagnosed with prostate cancer at some point are still alive today.
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 accounts for about 11% of cancer-related deaths in men.
The 5-year survival rate refers to the percentage of patients who live at least 5 years after their cancer is diagnosed. These rates are used to create a standard way of discussing prognosis (outlook). Of course, many of these patients live much longer than 5 years after diagnosis. Five-year survival rates are based on patients diagnosed and first treated more than 5 years ago. Improvements in treatment since then may result in a better outlook for recently diagnosed patients. Five-year relative survival rates compare the observed survival with that expected for people without the cancer. That means that relative survival only talks about deaths from the cancer in question. This is a more accurate way to describe the outlook for patients with a certain cancer.
According to the most recent data, for all men with prostate cancer, the relative 5-year survival rate is nearly100% and the relative 10-year survival rate is 91%. The 15-year relative survival rate is 76%. Keep in mind that 5-year survival rates are based on patients diagnosed and first treated more than 5 years ago, and 10-year survival rates are based on patients diagnosed more than 10 years ago. Modern methods of detection and treatment mean that many prostate cancers are now found earlier and can be treated more effectively. If you are diagnosed this year, your outlook is likely to be better than the numbers reported above.
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. For example, exposing skin to strong sunlight is a risk factor for skin cancer. Smoking is a risk factor for many cancers.
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 no known risk factors.
We don't yet completely understand the causes of prostate cancer, but researchers have found several factors that may change the risk of getting it. For some of these factors, the link to prostate cancer risk is not yet clear.
Age
Age is the strongest risk factor for prostate cancer. Prostate cancer is very rare before the age of 40, but the chance of having prostate cancer rises rapidly after age 50. Almost 2 out of 3 prostate cancers are found in men over the age of 65.
Race/ethnicity
Prostate cancer occurs more often in African-American men 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 likely accounts for at least part of this difference, but other factors are likely to be important as well. For example, lifestyle differences (diet, etc.) may be important: 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 with an affected brother 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 genes 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 genes is not yet available. Recently, some common gene variations have been linked to the risk of prostate cancer. Studies to confirm these results are needed to see if testing for the gene variants will be useful in predicting prostate cancer risk.
Some inherited genes raise the risk for more than one type of cancer. For example, inherited mutations of the BRCA1 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.
Diet
The exact role of diet in prostate cancer is not clear, but several different 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 advanced prostate cancer. 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 (having a high amount of extra body fat) is linked with a higher risk of getting prostate cancer. 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. 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 this was not seen in other studies.
Exercise
Exercise has not been shown to reduce prostate cancer risk in most studies. But some studies have found that high levels of physical activity, particularly in older men, may lower the risk of advanced prostate cancer. More research in this area is needed.
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.
Infection
Researchers have also looked to see if sexually transmitted infections (like gonorrhea or chlamydia) might increase the risk of prostate cancer, possibly by leading 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 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.