Prostate cancer is a disease in which cancer develops in the prostate, a gland in the male reproductive system. It occurs when cells of the prostate mutate and begin to multiply out of control. These cells may spread (metastasize) from the prostate to other parts of the body, especially the bones and lymph nodes. Prostate cancer may cause pain, difficulty in urinating, erectile dysfunction and other symptoms.
Rates of prostate cancer vary widely across the world. Although the rates vary widely between countries, it is least common in South and East Asia, more common in Europe, and most common in the United States. According to the American Cancer Society, prostate cancer is least common among Asian men and most common among black men, with figures for white men in-between. However, these high rates may be affected by increasing rates of detection.
Prostate cancer develops most frequently in men over fifty. This cancer can occur only in men, as the prostate is exclusively of the male reproductive tract. It is the most common type of cancer in men in the United States, where it is responsible for more male deaths than any other cancer, except lung cancer. In the UK it is also the second most common cause of cancer death after lung cancer. Around 35,000 men in the UK are diagnosed per year; where around 10,000 die of it. However, many men who develop prostate cancer never have symptoms, undergo no therapy, and eventually die of other causes. That is because malignant neoplasms of the prostate are, in most cases, slow-growing, and because most of those affected are very old. Hence they often die of causes unrelated to the prostate cancer, such as heart/circulatory disease, pneumonia, other unconnected cancers or old age. Many factors, including genetics and diet, have been implicated in the development of prostate cancer.
Prostate cancer is most often discovered by physical examination or by screening blood tests, such as the PSA (prostate specific antigen) test. There is some current concern about the accuracy of the PSA test and its usefulness. Suspected prostate cancer is typically confirmed by removing a piece of the prostate (biopsy) and examining it under a microscope. Further tests, such as X-rays and bone scans, may be performed to determine whether prostate cancer has spread.
Prostate cancer can be treated with surgery, radiation therapy, hormonal therapy, occasionally chemotherapy, proton therapy, or some combination of these. The age and underlying health of the man as well as the extent of spread, appearance under the microscope, and response of the cancer to initial treatment are important in determining the outcome of the disease. Since prostate cancer is a disease of older men, many will die of other causes before a slowly advancing prostate cancer can spread or cause symptoms. This makes treatment selection difficult. The decision whether or not to treat localized prostate cancer (a tumor that is contained within the prostate) with curative intent is a patient trade-off between the expected beneficial and harmful effects in terms of patient survival and quality of life.
The prostate is a part of the male reproductive organ which helps make and store seminal fluid. In adult men a typical prostate is about three centimeters long and weighs about twenty grams. It is located in the pelvis, under the urinary bladder and in front of the rectum. The prostate surrounds part of the urethra, the tube that carries urine from the bladder during urination and semen during ejaculation. Because of its location, prostate diseases often affect urination, ejaculation, and rarely defecation. The prostate contains many small glands which make about twenty percent of the fluid constituting semen. In prostate cancer the cells of these prostate glands mutate into cancer cells. The prostate glands require male hormones, known as androgens, to work properly. Androgens include testosterone, which is made in the testes; dehydroepiandrosterone, made in the adrenal glands; and dihydrotestosterone, which is converted from testosterone within the prostate itself. Androgens are also responsible for secondary sex characteristics such as facial hair and increased muscle mass.
Early prostate cancer usually causes no symptoms. Often it is diagnosed during the workup for an elevated PSA noticed during a routine checkup. Sometimes, however, prostate cancer does cause symptoms, often similar to those of diseases such as benign prostatic hypertrophy. These include frequent urination, increased urination at night, difficulty starting and maintaining a steady stream of urine, blood in the urine, and painful urination. Prostate cancer is associated with urinary disfunction as the prostate gland surrounds the prostatic urethra. Changes within the gland therefore directly affect urinary function. Prostate cancer may also cause problems with sexual function, such as difficulty achieving erection or painful ejaculation. The Vas deferens deposits seminal fluid into the prostatic urethra and secretions from the prostate gland itself are included in semen content, which is why Prosate Cancer can affect sexual performance and cause painful ejaculation.
Advanced prostate cancer can spread to other parts of the body and this may cause additional symptoms. The most common symptom being bone pain, often in vertebrae (bones of the spine), pelvis or ribs. Spread of Cancer into other bones such as the femur is usually to the proximal part of the bone. Prostate cancer in the spine can also compress the spinal cord, causing leg weakness and urinary and fecal incontinence.
Prostate cancer is classified as an adenocarcinoma, or glandular cancer, that begins when normal semen-secreting prostate gland cells mutate into cancer cells. The region of prostate gland where the adenocarcinoma is most common is the peripheral zone. Initially, small clumps of cancer cells remain confined to otherwise normal prostate glands, a condition known as carcinoma in situ or prostatic intraepithelial neoplasia (PIN). Although there is no proof that PIN is a cancer precursor, it is closely associated with cancer. Over time these cancer cells begin to multiply and spread to the surrounding prostate tissue (the stroma) forming a tumor. Eventually, the tumor may grow large enough to invade nearby organs such as the seminal vesicles or the rectum, or the tumor cells may develop the ability to travel in the bloodstream and lymphatic system. Prostate cancer is considered a malignant tumor because it is a mass of cells which can invade other parts of the body. This invasion of other organs is called metastasis. Prostate cancer most commonly metastasizes to the bones, lymph nodes, rectum, and bladder.
The specific causes of prostate cancer remain unknown. A man's risk of developing prostate cancer is related to his age, genetics, race, diet, lifestyle, medications, and other factors. The primary risk factor is age. Prostate cancer is uncommon in men less than 45, but becomes more common with advancing age. The average age at the time of diagnosis is 70. However, many men never know they have prostate cancer. Autopsy studies of Chinese, German, Israeli, Jamaican, Swedish, and Ugandan men who died of other causes have found prostate cancer in thirty percent of men in their 50s, and in eighty percent of men in their 70s.In the year 2005 in the United States, there were an estimated 230,000 new cases of prostate cancer and 30,000 deaths due to prostate cancer.
A man's genetic background contributes to his risk of developing prostate cancer. This is suggested by an increased incidence of prostate cancer found in certain racial groups, in identical twins of men with prostate cancer, and in men with certain genes. In the United States, prostate cancer more commonly affects black men than white or Hispanic men, and is also more deadly in black men. Men who have a brother or father with prostate cancer have twice the usual risk of developing prostate cancer. Studies of twins in Scandinavia suggest that forty percent of prostate cancer risk can be explained by inherited factors. However, no single gene is responsible for prostate cancer; many different genes have been implicated. Two genes (BRCA1 and BRCA2) that are important risk factors for ovarian cancer and breast cancer in women have also been implicated in prostate cancer.
Dietary amounts of certain foods, vitamins, and minerals can contribute to prostate cancer risk. Men with higher serum levels of the short-chain ?-6 fatty acid linoleic acid have higher rates of prostate cancer. However, the same series of studies showed that men with elevated levels of long-chain ?-3 (EPA and DHA) had lowered incidence. A long-term study reports that "blood levels of trans fatty acids, in particular trans fats resulting from the hydrogenation of vegetable oils, are associated with an increased prostate cancer risk." Other dietary factors that may increase prostate cancer risk include low intake of vitamin E (Vitamin E is found in green, leafy vegetables), omega-3 fatty acids (found in fatty fishes like salmon), and the mineral selenium. A study in 2007 cast doubt on the effectiveness of lycopene (found in tomatoes) in reducing the risk of prostate cancer. Lower blood levels of vitamin D also may increase the risk of developing prostate cancer. This may be linked to lower exposure to ultraviolet (UV) light, since UV light exposure can increase vitamin D in the body.
There are also some links between prostate cancer and medications, medical procedures, and medical conditions. Daily use of anti-inflammatory medicines such as aspirin, ibuprofen, or naproxen may decrease prostate cancer risk. Use of the cholesterol-lowering drugs known as the statins may also decrease prostate cancer risk. More frequent ejaculation also may decrease a man's risk of prostate cancer. One study showed that men who ejaculated five times a week in their 20s had a decreased rate of prostate cancer, though others have shown no benefit. Infection or inflammation of the prostate (prostatitis) may increase the chance for prostate cancer. In particular, infection with the sexually transmitted infections chlamydia, gonorrhea, or syphilis seems to increase risk. Finally, obesity and elevated blood levels of testosterone may increase the risk for prostate cancer.
Research released in May 2007, found that US war veterans who had been exposed to Agent Orange had a 48% increased risk of prostate cancer recurrence following surgery.
Prostate cancer risk can be decreased by modifying known risk factors for prostate cancer, such as decreasing intake of animal fat.
One research study, by the Cancer Council Victoria, has shown that men who report that they regularly ("more than five times per week") masturbate have up to one third fewer occurrences of prostate cancer. The researchers hypothesize that this could be because regular ejaculation reduces the buildup of carcinogenic deposits such as 3-methylcholanthrene is produced from the breakdown of cholesterol, which could damage the cells lining the prostate. The researchers also speculated that frequent ejaculation may cause the prostate to mature fully, making it less susceptible to carcinogens. It is also possible that there is another factor (such as hormone levels) that is a common cause of both a reduced susceptibility to prostate cancer and a tendency toward frequent masturbation. There is also some evidence that frequent sexual intercourse is associated with reduced risk of prostate cancer, although contrarily the risks associated with STDs have been shown to increase the risk of prostate cancer. Once the lining of the prostate is affected with cancer, the only known treatments are surgery and radiation therapy. Both may limit the ability to have erections afterward.
Several medications and vitamins may also help prevent prostate cancer. Two dietary supplements, vitamin E and selenium, may help prevent prostate cancer when taken daily. Estrogens from fermented soybeans and other plant sources (called phytoestrogens) may also help prevent prostate cancer. The selective estrogen receptor modulator drug toremifene has shown promise in early trials. Two medications which block the conversion of testosterone to dihydrotestosterone, finasteride and dutasteride, have also shown some promise. The use of these medications for primary prevention is still in the testing phase, and they are not widely used for this purpose. The problem with these medications is that they may preferentially block the development of lower-grade prostate tumors, leading to a relatively greater chance of higher grade cancers, and negating any overall survival improvement. Green tea may be protective (due to its polyphenol content), though the data is mixed. A 2006 study of green tea derivatives demonstrated promising prostate cancer prevention in patients at high risk for the disease. In 2003, an Australian research team led by Graham Giles of The Cancer Council Australia concluded that frequent masturbation by males appears to help prevent the development of prostate cancer. Recent research published in the Journal of the National Cancer Institute suggests that taking multivitamins more than seven times a week can increase the risks of contracting the disease. This research was unable to highlight the exact vitamins responsible for this increase (almost double), although they suggest that vitamin A, vitamin E and beta-carotene may lie at its heart. It is advised that those taking multivitamins never exceed the stated daily dose on the label. Scientists recommend a healthy, well balanced diet rich in fiber, and to reduce intake of meat. A 2007 study published in the Journal of the National Cancer Institute found that men eating cauliflower, broccoli, or one of the other cruciferous vegetables, more than once a week were 40% less likely to develop prostate cancer than men who rarely ate those vegetables. Scientists believe the reason for this phenomenon has to do with a phytochemical called Diindolylmethane in these vegetables that has Anti-Androgenic and immune modulating properties. This compound is currently under investigation by the National Cancer Institute as a natural therapeutic for prostate cancer. Australian research concluded that the more men ejaculate between the ages of 20 and 50, the less likely they are to develop prostate cancer. The protective effect is greatest while men are in their twenties: those who had ejaculated more than five times per week in their twenties, for instance, were one-third less likely to develop aggressive prostate cancer later in life. The results contradict those of previous studies, which have suggested that having had many sexual partners, or a high frequency of sexual activity, increases the risk of prostate cancer by up to 40 per cent. The key difference is that these earlier studies defined sexual activity as sexual intercourse, whereas the latest study focused on the number of ejaculations, whether or not intercourse was involved.
Prostate cancer screening is an attempt to find unsuspected cancers. Screening tests may lead to more specific follow-up tests such as a biopsy, where small pieces of the prostate are removed for closer study. Prostate cancer screening options include the digital rectal exam and the prostate specific antigen (PSA) blood test. Screening for prostate cancer is controversial because it is not clear if the benefits of screening outweigh the risks of follow-up diagnostic tests and cancer treatments.
Prostate cancer is usually a slow-growing cancer, very common among older men. In fact, most prostate cancers never grow to the point where they cause symptoms, and most men with prostate cancer die of other causes before prostate cancer has an impact on their lives. The PSA screening test may detect these small cancers that would never become life threatening. Doing the PSA test in these men may lead to overdiagnosis, including additional testing and treatment. Follow-up tests, such as prostate biopsy, may cause pain, bleeding and infection. Prostate cancer treatments may cause urinary incontinence and erectile dysfunction. Therefore, it is essential that the risks and benefits of diagnostic procedures and treatment be carefully considered before PSA screening.
No major scientific or medical organizations currently support routine screening for prostate cancer.
* In 2002, the U.S. Preventive Services Task Force (USPSTF) concluded that the evidence was insufficient to recommend for or against routine screening for prostate cancer using PSA testing or digital rectal examination (DRE). The previous 1995 USPSTF recommendation was against routine screening.
* In 1997, American Cancer Society (ACS) guidelines began recommending that beginning at age 50 (age 45 for African-American men and men with a family history of prostate cancer, and since 2001, age 40 for men with a very strong family history of prostate cancer), PSA testing and DRE be offered annually to men who have a life-expectancy of 10 or more years (average life expectancy is 10 years or more for U.S. men under age 76) along with information on the risks and benefits of screening. The previous ACS recommendations since 1980 had been for routine screening for prostate cancer with DRE annually beginning at age 40, and since 1992 had been for routine screening with DRE and PSA testing annually beginning at age 50.
* The 2007 National Comprehensive Cancer Network (NCCN) guideline recommends offering a baseline PSA test and DRE at ages 40 and 45 and annual PSA testing and DRE beginning at age 50 (with annual PSA testing and DRE beginning at age 40 for African-American men, men with a family history of prostate cancer, and men with a PSA = 0.6 ng/mL at age 40 or PSA > 0.6 ng/mL at age 45) through age 80, along with information on the risks and benefits of screening. Biopsy is recommended if DRE is positive or PSA = 4 ng/mL, and biopsy considered if PSA > 2.5 ng/mL or PSA velocity = 0.35 ng/mL/year when PSA = 2.5 ng/mL.
* Some U.S. radiation oncologists and medical oncologists who specialize in treating prostate cancer recommend obtaining a baseline PSA in all men at age 35 or beginning annual PSA testing in high risk men at age 35.
Since there is no firm evidence or general agreement that the benefits of PSA screening outweigh the harms, major scientific and medical organizations recommend that clinicians use a process of shared decision-making that includes discussing with patients the risks of prostate cancer, the potential benefits and harms of screening, and involving the patients in the decision.[54]
However, because PSA screening is widespread in the United States, following the recommendations of major scientific and medical organizations to use shared decision-making is legally perilous in some U.S. states.[55] In 2003, a Virginia jury found a family practice residency program guilty of malpractice and liable for $1 million for following national guidelines and using shared decision-making, thereby allowing a patient (subsequently found to have a high PSA and incurable advanced prostate cancer) to decline a screening PSA test, instead of routinely ordering without discussion PSA tests in all men = 50 years of age as four local physicians testified was their practice, and was accepted by the jury as the local standard of care.[56]
An estimated 20 million PSA tests are done per year in North America and possibly 20 million more outside of North America.[57]
* In 2000, 34.1% of all U.S. men age = 50 had a screening PSA test within the past year and 56.8% reported ever having a PSA test.[54]
* In 2000, 33.6% of all U.S. men age 50–64 and 51.3% of men age = 65 had a PSA test within the past year.[58]
* In 2005, 33.5% of all U.S. men age 50–64 had a PSA test in the past year.
o 37.5% of men with private health insurance, 20.8% of men with Medicaid insurance, 14.0% of currently uninsured men, and 11.5% of men uninsured for > 12 months.[59]
* In 2000–2001, 34.1% of all Canadian men age = 50 had a screening PSA test within the past year and 47.5% reported ever having a screening PSA test.[60]
* Canadian men in Ontario were most likely to have had a PSA test within the past year and men in Alberta were least likely to have had a PSA test with the past year or ever.[61]
Digital rectal examination (DRE) is a procedure where the examiner inserts a gloved, lubricated finger into the rectum to check the size, shape, and texture of the prostate. Areas which are irregular, hard or lumpy need further evaluation, since they may contain cancer. Although the DRE only evaluates the back of the prostate, 85% of prostate cancers arise in this part of the prostate. Prostate cancer which can be felt on DRE is generally more advanced.[62] The use of DRE has never been shown to prevent prostate cancer deaths when used as the only screening test.[63]
The PSA test measures the blood level of prostate-specific antigen, an enzyme produced by the prostate. Specifically, PSA is a serine protease similar to kallikrein. Its normal function is to liquify gelatinous semen after ejaculation, allowing spermatozoa to more easily navigate through the uterine cervix.
The risk of prostate cancer increases with increasing PSA levels.[64] 4 ng/mL was chosen arbitrarily as a decision level for biopsies in the clinical trial upon which the FDA in 1994 based adding prostate cancer detection in men age 50 and over as an approved indication for the first commercially available PSA test.[65] 4 ng/mL was used as the biopsy decision level in the PLCO trial, 3 ng/mL was used in the ERSPC and ProtecT trials, and 2.5 ng/mL is used in the 2007 NCCN guideline.
PSA levels can change for many reasons other than cancer. Two common causes of high PSA levels are enlargement of the prostate (benign prostatic hypertrophy (BPH)) and infection in the prostate (prostatitis). It can also be raised for 24 hours after ejaculation and several days after catheterization. PSA levels are lowered in men who use medications used to treat BPH or baldness. These medications, finasteride (marketed as Proscar or Propecia) and dutasteride (marketed as Avodart), may decrease the PSA levels by 50% or more.
Several other ways of evaluating the PSA have been developed to avoid the shortcomings of simple PSA screening. The use of age-specific reference ranges improves the sensitivity and specificity of the test. The rate of rise of the PSA over time, called the PSA velocity, has been used to evaluate men with PSA levels between 4 and 10 ng/ml, but it has not proven to be an effective screening test.[66] Comparing the PSA level with the size of the prostate, as measured by ultrasound or magnetic resonance imaging, has also been studied. This comparison, called PSA density, is both costly and has not proven to be an effective screening test.[67] PSA in the blood may either be free or bound to other proteins. Measuring the amount of PSA which is free or bound may provide additional screening information, but questions regarding the usefulness of these measurements limit their widespread use.[6
Treatment for prostate cancer may involve watchful waiting, surgery, radiation therapy including brachytherapy, High Intensity Focused Ultrasound (HIFU), chemotherapy, cryosurgery, hormonal therapy, or some combination. Which option is best depends on the stage of the disease, the Gleason score, and the PSA level. Other important factors are the man's age, his general health, and his feelings about potential treatments and their possible side effects. Because all treatments can have significant side effects, such as erectile dysfunction and urinary incontinence, treatment discussions often focus on balancing the goals of therapy with the risks of lifestyle alterations.
The selection of treatment options may be a complex decision involving many factors. For example, radical prostatectomy after primary radiation failure is a very technically challenging surgery and may not be an option.[76] This may enter into the treatment decision.
If the cancer has spread beyond the prostate, treatment options significantly change, so most doctors who treat prostate cancer use a variety of nomograms to predict the probability of spread. Treatment by watchful waiting, HIFU, radiation therapy, cryosurgery, and surgery are generally offered to men whose cancer remains within the prostate. Hormonal therapy and chemotherapy are often reserved for disease which has spread beyond the prostate. However, there are exceptions: radiation therapy may be used for some advanced tumors, and hormonal therapy is used for some early stage tumors. Cryotherapy, hormonal therapy, and chemotherapy may also be offered if initial treatment fails and the cancer progresses.
