What is prostate cancer?
Table of Contents:
Prostate cancer is a malignant growth of the glandular cells of the prostate. Our body is composed of billions of cells; they are the smallest unit in the body. Normally, each cell functions for a while, then dies and is replaced in an organized manner. This results in the appropriate number of cells being present to carry out necessary cell functions. Sometimes there can be an uncontrolled replacement of cells, leaving the cells unable to organize as they did before. Such abnormal growth of cells is called a tumor. Tumors may be benign (noncancerous)
or malignant (cancerous). Cancer is abnormal cell growth and disorder such that the cancer cells can grow without the normal controls and limits. A malignancy is a cancerous growth that has the potential to spread and cause damage to other tissues of the body or even lead to death. Cancers can spread locally into surrounding tissues, or cancer cells can break away from the tumor and enter body fluids, such as the blood and lymph, and spread to other parts of the body. Lymph is an almost clear fluid that drains waste from cells. This fluid travels in vessels to the lymph nodes, small bean-shaped structures that filter unwanted substances, such as cancer cells and bacteria, out of the fluid. Lymph nodes may become filled with cancer cells.
As with most cancers, prostate cancer is not contagious.
How common is prostate cancer?
There are more than 100 different types of cancer. In the United States, a man has a 50% chance of developing some type of cancer in his lifetime. In American men, (excluding skin cancer) prostate cancer is the most common cancer. Prostate cancer accounts for about 33% (234,460) of cases of cancer (Table 2). More than 75% of the cases of prostate cancer are diagnosed in men older than 65 years. Based on cases diagnosed between 1995 and 2001, it is estimated that 91% of the new cases of prostate cancer are expected to be diagnosed at local or regional stages (see staging of prostate cancer), for which 5-year survival is nearly 100%. It is estimated that prostate cancer will be the cause of death in 9% of men, 27,350 prostate cancer related deaths. In the United States, deaths from prostate cancer have decreased significantly by 4.1% per year from 1994 to 2004. Most notably, the death rate for African American men in the United States has decreased by 6%.
Table 2. Cancer Statistics for Men in the United States—2006
Reprinted with permission from Ahnedub GM, Suegek RM, Ward E et al. Cancer Statistics, 2006. CA Cancer J Clin 2006;56:106-130 [published erratum appears in CA Cancer J Clin 2006;56:109].
What are the risk factors for prostate cancer, and who is at risk? Is there anything that decreases the risk of developing prostate cancer?
Theoretically, all men are at risk for developing prostate cancer. The prevalence of prostate cancer increases with age, and the increase with age is greater for prostate cancer than for any other cancer.
<39 years of age 1:103
40-59 years of age 1:8
60-79 years of age
Basically, every 10 years after the age of 40 years, the incidence of prostate cancer nearly doubles, with a risk of 10% for men in their 50s increasing to 70% for those in their 80s. However, in most older men, the prostate cancer does not grow and many die of other causes and are not identified as having prostate cancer before their death.
Prostate cancer is 66% more common among African Americans, and it is twice as likely to be fatal in African Americans as in Caucasians. However, blacks in Africa have one of the lowest rates of prostate cancer in the world. Males of Asian descent living in the United States have lower rates of prostate cancer than Caucasians, but higher rates than Asian males in their native countries. Japan appears to have the lowest prostate cancer death rate, compared with Switzerland, which has the highest (Figure 4).
Figure 4. International prostate cancer incidence rates—1998.
Standford J.L, Stephenson RA, Coyle LM et al. Prostate Cancer Trends 1973—1995. Bethesda, MD. Cancer Surveillence, Epidemiology, and End Results (SEER) Program, National Cancer Institute 1998.
Prostate cancer is related to sex hormones. Prostate cancer rarely develops in men who had their testicles removed (castration) at an early age. There is a correlation between prostate cancer and high levels of testosterone. There does not appear to be any clear correlation between body size and risk of prostate cancer but men with prostate cancer who had weight gain in early adulthood tend to have more aggressive cancers. Smoking does not appear to increase your risk of cancer, though smokers tend to have more aggressive cancer than non-smokers. Physical activity appears to decrease the risk of prostate cancer.
The effects of vasectomy on the risk of prostate cancer are unclear. Some studies have demonstrated an increased risk of prostate cancer with vasectomy, but these individuals tended to have a lower grade, lower stage prostate cancer that is associated with a better prognosis. Other studies have failed to confirm an increased risk of prostate cancer after vasectomy. Vasectomy is the minor surgical sterilization procedure in which the vas deferens (the sperm duct) is cut and either clipped, tied, or cauterized to prevent it from reattaching itself. Vasectomy does not affect testosterone production or release of testosterone from the testicles into the bloodstream; it only prevents sperm from leaving the testis. Current medical wisdom holds that vasectomy does not increase your risk of prostate cancer.
The Cancer Risk Calculator for Prostate Cancer has been developed as a tool to help identify one's risk of having prostate cancer. The calculator may be applied to men age 50 years or older, with no previous diagnosis of prostate cancer and DRE and PSA results less than 1 year old. The calculator may also be applied to men undergoing prostate cancer screening with PSA and
DRE, as it was developed from the Prostate Cancer Prevention Trial. The calculator is designed to provide a preliminary assessment of risk of prostate cancer if a prostate biopsy is performed. One can find the prostate cancer risk calculator online, either by searching for "cancer risk calculator for prostate cancer" or by going to the National Cancer Institute website and looking under early detection research network.
A recent study called the "Prostate Cancer Prevention Trial" (PCPT) demonstrated that finasteride (Proscar) at a dose of 5mg/day decreases the likelihood of developing prostate cancer by 26% when compared to placebo (sugar pill). In addition, finasteride decreased the risk of high grade PIN (which may be a precursor of prostate cancer) by about the same rate. In this study, finasteride lowered the PSA by 50% after 2 months of treatment.
Results of the "Reduction by Dutasteride of Prostate Cancer" (REDUCE) trial showed that the 5-alpha-reductase inhibitor dutasteride at doses of 0.5 mg/day decreased the relative risk of prostate cancer by 23% compared to placebo. Furthermore, the risk was markedly decreased in the number of high-grade tumors, with no absolute increase in incidence compared to placebo.
Dietary and genetic (hereditary) factors may also play a role in the risk of developing cancer.
In certain cases, it appears that the risk for prostate cancer is passed on to males in the family. The younger the family member is when he is diagnosed with prostate cancer, the higher the risk is for male relatives to have prostate cancer at a younger age. The risk also increases with the number of relatives affected with prostate cancer (Table 3).
It is thought that 9% of all prostate cancers, and more than 40% of prostate cancers occurring in younger males,
Table 3. Relative Risk for Prostate Cancer with Affected Relatives
Reprinted with permission from Carter BS, Bovea GS, Beaty TH et al. J Uroi 1993;150:797-802.
are related to genetic causes. Abnormalities of genes of chromosomes 1 and the X chromosome are associated with an increased risk of prostate cancer. One such gene, the HPC1 gene, appears to cause about one third of all inherited cases of prostate cancer. There also appears to be a gene that is carried on the X chromosome (the chromosome passed on to the male by his mother) that may increase the risk of prostate cancer. This X chromosome related increased risk of prostate cancer might somehow play a part in the identification of a higher incidence of prostate cancer in male relatives of women with breast cancer.
Black men are more likely to get prostate cancer at a younger age, and they often have a more aggressive cancer. Of all population groups in the world, African American men have the highest rate of prostate cancer. The reason for this is not known. Because they are at higher risk, African American men should start prostate cancer screening at a younger age than Caucasian men.
A variety of dietary risk factors exist for prostate cancer. Several studies suggest that a high-fat diet stimulates prostate cancer to grow. In particular, beef and high-fat dairy products appear to be stimulators of prostate cancer. Conversely, a low-fat diet rich in fruits and vegetables may help decrease the risk of prostate cancer. Such healthful foods include soy (tofu and soy milk), tomatoes, green tea, red grapes, strawberries, raspberries, blueberries, peas, watermelon, rosemary, garlic, and citrus. Soy contains substances called phytoestrogens, which resemble the female sex hormone estrogen. In dietary-doses—that is, amounts normally found in foods, not the amounts in supplements—phytoestrogens can decrease the risk of prostate cancer. Green tea contains antioxidants, which are chemicals that help prevent changes in cells and reduce damage that can cause the cells to become cancerous.
Vitamin E is a free radical scavenger and is also associated with a decreased risk of prostate cancer, but men with a history of bleeding problems or who take blood thinners should discuss the use of vitamin E with their doctor before taking it.
A high intake of dairy products has also been associated with an increased risk of prostate cancer.
Vitamin D deficiency has been associated with an increased risk of prostate cancer.
High levels of fructose, a form of sugar, have been associated with a lower risk of prostate cancer. Selenium has been associated with a decreased risk of prostate cancer. Lycopene, a carotenoid (chemicals that give orange, red, or yellow coloring to plants), is associated with a decreased risk of prostate cancer. Lycopene is found in high levels in tomatoes and is beneficial only if one eats cooked tomatoes, such as tomato sauce, not tomato juice. Many studies are in the process of looking at the effects of such dietary risks.