Prostate Cancer

Prostate cancer is a disease in which cancer develops in the prostate, a gland of the male reproductive system that lies just below and in front of the urinary bladder. Like all cancers, prostate cancer is the uncontrolled growth of cells that have the potential to migrate and grow elsewhere in the body. Almost all cases of prostate cancer occur in men over the age of 50. The disease becomes increasingly common as men age. Most cases are diagnosed before symptoms appear. Several treatment options are available, and efforts to improve the quality of life of men with prostate cancer continue.

Types

Most cases of prostate cancer arise from epithelial cells that line the numerous ducts of the prostate gland; thus, they are termed adenocarcinomas. Other types of cells within the prostate can become malignant, but these are far less common.

Signs and Symptoms

Most cases of prostate cancer are diagnosed before symptoms appear because of widespread awareness and screening programs that detect the disease early in its course. If the disease is not detected early or not treated successfully, Sometimes, however, prostate cancer does cause symptoms, often similar to those of diseases such as benign prostatic hypertrophy. These include frequent or painful urination, difficulty starting and maintaining a steady stream of urine, or blood in the urine. Prostate cancer is associated with urinary dysfunction as the prostate gland surrounds the prostatic urethra. Changes within the gland therefore directly affect urinary function. Because the vas deferens deposits seminal fluid into the prostatic urethra, and secretions from the prostate gland itself are included in semen content, prostate cancer may also cause problems with sexual function and performance, such as difficulty achieving erection or painful ejaculation.^[1].

Advanced prostate cancer can spread to other parts of the body and this may cause additional symptoms. The most common symptom is bone pain, often in the vertebrae, 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 vertebral column can also compress the spinal cord, causing leg weakness and urinary incontinence and fecal incontinence.^[2]

Causes

The specific causes of prostate cancer remain unknown.^[3] A man's risk of developing prostate cancer is related to his age (the most important risk factor); other risk factors include his genetic background, diet, medical history, and other factors. 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.^[4]

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.^[5]

Dietary amounts of certain foods, vitamins, and dietary minerals can contribute to prostate cancer risk. Men with higher serum levels of the short-chain omega-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 fatty acids had a lowered incidence.^[6] 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.^[7] Finally, obesity^[8] may increase the risk for prostate cancer.

Diagnosis

Prostate cancer is most often discovered by PSA (prostate specific antigen) screening and less commonly by physical examination or by symptoms. There is some current concern about the accuracy of the PSA test and its usefulness. The search continues for biomarkers that will allow early diagnosis of cancer while not identifying cancer in those who are truly cancer-free.^[9] Suspected prostate cancer is typically confirmed by taking a biopsy of the prostate to be examined by a pathologist. Further tests, such as CT scans and bone scans, may be performed to determine whether prostate cancer has spread.

Treatment

There are many treatment options for prostate cancer. Choices where the intent is to cure are primarily surgery and radiation therapy. Other treatments such as hormonal therapy, chemotherapy, proton therapy, cryosurgery, high intensity focused ultrasound (HIFU) also exist depending on the clinical scenario and desired outcome. 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. 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.

Prevention

Vitamins and medication

Evidence from epidemiological studies supports protective roles in reducing prostate cancer for dietary selenium, vitamin E, lycopene, and soy foods. High plasma levels of Vitamin D may also have a protective effect.^[10] Estrogens from fermented soybeans and other plant sources (called phytoestrogens) may also help prevent prostate cancer.^[11] The selective estrogen receptor modulator drug toremifene has shown promise in early trials.^[12][13] Two medications which block the conversion of testosterone to dihydrotestosterone, finasteride^[14] and dutasteride,^[15] 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 initial 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. More recent research found that finasteride did not increase the percentage of higher grade cancers. A 2008 study update found that finasteride reduces the incidence of prostate cancer by 30%. In the original study it turns that that the smaller prostate caused by finasteride means that a doctor is more likely to hit upon cancer nests and more likely to find aggressive-looking cells. Most of the men in the study who had cancer — aggressive or not — chose to be treated and many had their prostates removed. A pathologist then carefully examined every one of those 500 prostates and compared the kinds of cancers found at surgery to those initially diagnosed at biopsy. Finasteride did not increase the risk of High-Grade prostate cancer.^[16][17]

Ejaculation frequency

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.^[18][19] 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 percent. The key difference is that these earlier studies defined sexual activity as sexual intercourse, whereas this study focused on the number of ejaculations, whether or not intercourse was involved.^[20] Another study completed in 2004 reported that "Most categories of ejaculation frequency were unrelated to risk of prostate cancer. However, high ejaculation frequency was related to decreased risk of total prostate cancer." The report abstract concluded, "Our results suggest that ejaculation frequency is not related to increased risk of prostate cancer." ^[21]

Screening

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 cores 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.

Since there is no general agreement that the benefits of PSA screening outweigh the harms, the consensus is 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.

Digital rectal examination

Digital rectal examination. Source:NCI

Prostate specific antigen

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 Spermatozoon|spermatozoa to more easily navigate through the uterine cervix.

The risk of prostate cancer increases with increasing PSA levels. 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.^[23]

Diagnosis

When a man has symptoms of prostate cancer, or a screening test indicates an increased risk for cancer, more invasive evaluation is offered.

The only test which can fully confirm the diagnosis of prostate cancer is a biopsy, the removal of small pieces of the prostate for examination by a pathologist. However, prior to a biopsy, several other tools may be used to gather more information about the prostate and the urinary tract. Cystoscopy shows the urinary tract from inside the bladder, using a thin, flexible camera tube inserted down the urethra. Transrectal ultrasonography creates a picture of the prostate using sound waves from a probe in the rectum.

Prostate Biopsy

If cancer is suspected, a biopsy is offered. During a biopsy a urologist or radiologist obtains tissue samples from the prostate via the rectum. A biopsy gun inserts and removes special hollow-core needles (usually three to six on each side of the prostate) in less than a second. Prostate biopsies are routinely done on an outpatient basis and rarely require hospitalization. Fifty-five percent of men report discomfort during prostate biopsy.^[24]

Pathology evaluation

The tissue samples are then sent to a medical laboratory, prepared for histology and thin slices examined by a pathologist with a microscope. The pathologist will evaluate whether cancer cells are present, the grade of the cancer (or Gleason score), the size of the cancer and whether it has spread outside of the prostate or not. In difficult cases, immunhistochemistry for high molecular weight cytokeratin and P504S may help confirm the diagnosis of cancer.

Biopsy of Metastases

Biopsies from tumors outside of the prostate are occasionally taken to determine if they represent metastasis from a prostate cancer. In these cases, immunohistochemistry for PSA and other tumor markers are useful.^[25]

New tests being investigated

Currently, an active area of research involves non-invasive methods of prostate tumor detection. Adenoviruses modified to transfect tumor cells with harmless yet distinct genes (such as luciferase) have proven capable of early detection. So far, though, this area of research has only been tested in animal and LNCaP models.^[26]

Staging

An important part of evaluating prostate cancer is determining the stage, or how far the cancer has spread. Knowing the stage helps define prognosis and is useful when selecting therapies. The most common system is the four-stage TNM system (abbreviated from Tumor/Nodes/Metastases). Its components include the size of the tumor, the number of involved lymph nodes, and the presence of any other metastases.

The most important distinction made by any staging system is whether or not the cancer is still confined to the prostate. In the TNM system, clinical T1 and T2 cancers are found only in the prostate, while T3 and T4 cancers have spread elsewhere. Several tests can be used to look for evidence of spread. These include computed tomography to evaluate spread within the pelvis, bone scans to look for spread to the bones, and endorectal coil magnetic resonance imaging to closely evaluate the prostatic capsule and the seminal vesicles. Bone scans should reveal osteoblastic appearance due to increased bone density in the areas of bone metastasis - opposite to what is found in many other cancers that metastasize.

Computed tomography (CT) and magnetic resonance imaging (MRI) currently do not add any significant information in the assessment of possible lymph node metastases in patients with prostate cancer according to a meta-analysis.^[27] The sensitivity of CT was 42% and specificity of CT was 82%. The sensitivity of MRI was 39% and the specificity of MRI was 82%. For patients at similar risk to those in this study (17% had positive pelvic lymph nodes in the CT studies and 30% had positive pelvic lymph nodes in the MRI studies), this leads to a positive predictive value (PPV) of 32.3% with CT, 48.1% with MRI, and negative predictive value (NPV) of 87.3% with CT, 75.8% with MRI.

After a prostate biopsy, a pathologist looks at the samples under a microscope. If cancer is present, the pathologist reports the grade of the tumor. The grade tells how much the tumor tissue differs from normal prostate tissue and suggests how fast the tumor is likely to grow. The Gleason system is used to grade prostate tumors from 2 to 10, where a Gleason score of 10 indicates the most abnormalities. The pathologist assigns a number from 1 to 5 for the most common pattern observed under the microscope, then does the same for the second most common pattern. The sum of these two numbers is the Gleason score. The Whitmore-Jewett stage is another method sometimes used. Proper grading of the tumor is critical, since the grade of the tumor is one of the major factors used to determine the treatment recommendation.

Risk assessment

Many prostate cancers are not destined to be lethal, and most men will ultimately die from causes other than of the disease. Decisions about treatment type and timing may therefore be informed by an estimation of the risk that the tumor will ultimately recur after treatment and/or progress to metastases and mortality. Several tools are available to help predict outcomes such as pathologic stage and recurrence after surgery or radiation therapy. Most combine stage, grade, and PSA level, and some also add the number or percent of biopsy cores positive, age, and/or other information.

The D’Amico classification stratifies men to low, intermediate, or high risk based on stage, grade, and PSA. It is used widely in clinical practice and research settings. The major downside to the 3-level system is that it does not account for multiple adverse parameters (e.g., high Gleason score and high PSA) in stratifying patients.

The Partin tables predict pathologic outcomes (margin status, extraprostatic extension, and seminal vesicle invasion) based on the same 3 variables, and are published as lookup tables.

The Kattan nomograms predict recurrence after surgery and/or radiation therapy, based on data available either at time of diagnosis or after surgery. The nomograms can be calculated using paper graphs, or using software available on a website or for handheld computers. The Kattan score represents the likelihood of remaining free of disease at a given time interval following treatment.

The UCSF Cancer of the Prostate Risk Assessment (CAPRA) score predicts both pathologic status and recurrence after surgery. It offers comparable accuracy as the Kattan preoperative nomogram, and can be calculated without paper tables or a calculator. Points are assigned based on PSA, Grade, stage, age, and percent of cores positive; the sum yields a 0–10 score, with every 2 points representing roughly a doubling of risk of recurrence. The CAPRA score was derived from community-based data in the CaPSURE database. It has been validated among over 10,000 prostatectomy patients, including patients from CaPSURE; the SEARCH registry, representing data from several Veterans Administration and active military medical centers; a multi-institutional cohort in Germany; and the prostatectomy cohort at Johns Hopkins University.

Prognosis

In patients who undergo treatment, the most important clinical prognostic indicators of disease outcome are stage, pre-therapy PSA level and Gleason score. In general, the higher the grade and the stage, the poorer the prognosis. Nomograms can be used to calculate the estimated risk of the individual patient. The predictions are based on the experience of large groups of patients suffering from cancers at various stages.^[28]

Progression

In 1941, Charles Huggins reported that androgen ablation therapy causes regression of primary and metastatic androgen-dependent prostate cancer.^[29] Androgen ablation therapy causes remission in 80-90% of patients undergoing therapy, resulting in a median progression-free survival of 12 to 33 months. After remission an androgen-independent phenotype typically emerges, where the median overall survival is 23–37 months from the time of initiation of androgen ablation therapy.^[30]

Epidemiology

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.^[31]

Prostate Cancer Video

In this NHS Choices video, Chris Parker, a prostate cancer expert explains the symptoms and treatment options available. Phillip Kissi also describes his experience of being diagnosed with prostate cancer:

References

1. ↑ Miller DC, Hafez KS, Stewart A, Montie JE, Wei JT. Prostate carcinoma presentation, diagnosis, and staging: an update form the National Cancer Data Base. Cancer. 2003 Sep 15;98(6):1169-78. Abstract
2. ↑ van der Cruijsen-Koeter IW, Vis AN, Roobol MJ, et al. Comparison of screen detected and clinically diagnosed prostate cancer in the European randomized study of screening for prostate cancer, section Rotterdam. J Urol. 2005 Jul;174(1):121-5. Abstract
3. ↑ Hsing AW, Chokkalingam AP. Prostate cancer epidemiology. Front Biosci. 2006 May 1;11:1388-413. Abstract
4. ↑ Breslow N, Chan CW, Dhom G, et al. Latent carcinoma of prostate at autopsy in seven areas. The International Agency for Research on Cancer, Lyons, France. Int J Cancer. 1977 Nov 15;20(5):680-8. Abstract
5. ↑ Hoffman RM, Gilliland FD, Eley JW, et al. Racial and ethnic differences in advanced-stage prostate cancer: the Prostate Cancer Outcomes Study. J Natl Cancer Inst. 2001 Mar 7;93(5):388-95. Abstract
6. ↑ Chan JM, Gann PH, Giovannucci EL. Role of diet in prostate cancer development and progression. J Clin Oncol. 2005 Nov 10;23(32):8152-60. Abstract
7. ↑ Jacobs EJ, Rodriguez C, Mondul AM, et al. A large cohort study of aspirin and other nonsteroidal anti-inflammatory drugs and prostate cancer incidence. J Natl Cancer Inst. 2005 Jul 6;97(13):975-80. [http://pubmed.gov/15998950
8. ↑ Calle EE, Rodriguez C, Walker-Thurmond K, Thun MJ. Overweight, obesity, and mortality from cancer in a prospectively studied cohort of U.S. adults. N Engl J Med. 2003 Apr 24;348(17):1625-38. Abstract
9. ↑ Sardana G, Dowell B, Diamandis EP. Emerging biomarkers for the diagnosis and prognosis of prostate cancer. Clin Chem. 2008 Dec;54(12):1951-60. Abstract
10. ↑ Wigle DT, Turner MC, Gomes J, Parent ME. Role of hormonal and other factors in human prostate cancer |journal=J Toxicol Environ Health B Crit Rev |volume=11 |issue=3-4 |pages=242–59 |year=2008 |month=March |pmid=18368555 |doi=10.1080/10937400701873548 |url=}}
11. ↑ Template:Citation/core Erratum in: Nutr Cancer 2000;36(2):243.
12. ↑ Template:Citation/core
13. ↑ Template:Citation/core
14. ↑ Template:Citation/core
15. ↑ Template:Citation/core
16. ↑ Template:Cite newsNY Times date = June 15, 2008 | accessdate = 2008-06-15 }}
17. ↑ Template:Citation/core
18. ↑ [1]Giles, et al., Sexual factors and prostate cancer, BJU International, Volume 92 Issue 3, Ausust 2003, pp. 211-216
19. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named BBC_NEWS_Masturbation
20. ↑ Template:Cite web
21. ↑ Template:Citation/core
22. ↑ Chodak GW, Keller P, Schoenberg HW. Assessment of screening for prostate cancer using the digital rectal examination. J Urol. 1989 May;141(5):1136-8.Abstract
23. ↑ Thompson IM, Ankerst DP. Prostate-specific antigen in the early detection of prostate cancer. CMAJ. 2007 Jun 19;176(13):1853-8. Abstract | Full Text | PDF
24. ↑ Template:Citation/core
25. ↑ Template:Citation/core
26. ↑ Iyer M, Salazar FB, Lewis X, Zhang L, Wu L, Carey M and Gambhir SS. Non-invasive imaging of a transgenic mouse model using a prostate-specific two-step transcriptional amplification strategy. Transg Res.2005; 14(1): 47–55
27. ↑ Template:Citation/core
28. ↑ Di Blasio CJ, Rhee AC, Cho D, Scardino PT, Kattan MW. Predicting clinical end points: treatment nomograms in prostate cancer. Semin Oncol. 2003 Oct;30(5):567-86. Abstract
29. ↑ Huggins C, Steven RE and Hodges CV, Studies on prostatic cancer. Arch. Sug. 43:209–223, 1941.
30. ↑ Hellerstedt BA, Pienta KJ. The current state of hormonal therapy for prostate cancer. CA Cancer J Clin. 2002 May-Jun;52(3):154-79. Abstract
31. ↑ Potosky AL, Miller BA, Albertsen PC, Kramer BS. The role of increasing detection in the rising incidence of prostate cancer. JAMA. 1995 Feb 15;273(7):548-52. Abstract