Pushing on with my series of cancer awareness months, today I’m going to be writing about prostate cancer in observance of Prostate Cancer Awareness Month. After writing long posts for Childhood Cancer Awareness Month, Blood Cancer Awareness Month, and Ovarian/Gynecological Cancer Awareness Month, this post is hopefully going to be a bit more concise. However, that doesn’t mean prostate cancer isn’t as important as these other cancers. In fact, prostate cancer is the most common cancer in men outside of non-melanoma skin cancer and is the second leading cause of cancer death in men. So as a cancer advocate, I think it’s important to learn a bit more about this very common form of cancer!
About Prostate Cancer
The prostate is a gland within the male reproductive system that is located in front of the rectum and just below the bladder, where it surrounds the urethra. The prostate is responsible for producing the liquid component of the seminal fluid that helps to carry the sperm out of the body as part of the semen. The prostate grows rapidly during puberty in response to a testosterone derivative called dihydrotestosterone (or DHT). The healthy adult prostate is generally the size of a walnut and does not continue to grow larger with age, although a variety of conditions can result in an enlarged prostate. The most common of these conditions is called benign prostatic hyperplasia (or BHP), which generally only results in serious medical complications when the enlarged prostate begins to squeeze and constrict the urethra.
Prostate cancer, then, is any cancer that develops in the tissues of the prostate. Almost all prostate cancers are adenocarcinomas; that is, cancers that develop from the glandular cells of the prostate. Other (very rare) subtypes of prostate cancer include sarcomas (soft tissue cancers), small cell carcinomas, and transitional cell carcinomas. It is important to note that BHP is NOT a form of prostate cancer. While some prostate cancers can grow and spread very rapidly, the majority of prostate cancer grow incredibly slowly. These slow progressing cancers are often present within the prostate for years to decades before they begin to have any kind of symptomatic effects on the individual harboring the cancer.
While prostate cancer is not known to be caused by HPV infection, the slow growth of prostate tumors results in a long precancerous stage that is similar to that seen in cervical, vaginal, and vulvar cancers. These precancerous changes are known as prostatic intraepithelial neoplasia (or PIN) and can be classified as either high- or low-grade PIN. It is estimated that nearly half of all men will develop some degree of PIN by age 50. Men with high-grade PIN have a 20-30% chance of harboring prostate cancer at another site within the gland. The relationship between low-grade PIN is much less clear and may not be related to prostate cancer at all.
The primary risk factor for prostate cancer is age, with two-thirds of all prostate cancers being diagnosed in men over the age of 65. Prostate cancer is very rare in men under the age of 40. Certain races also appear to have a higher risk of prostate cancer. For example, prostate cancer is more common in African American men, who are also twice as likely to die from the disease. The reason for this increased risk is unknown at this time. A family history of prostate cancer is also linked to a higher risk of developing prostate cancer, with 5-10% of prostate cancers having a known genetic basis. Interestingly, while mutations in the BRCA1 and BRCA2 genes are most commonly associated with an increased risk of developing breast and ovarian cancer in women, mutations in these same genes also appear to be associated with an increased risk of prostate cancer. Finally, it appears that a diet high in red meat and dairy and low in fruits and vegetables may lead to an increased risk of prostate cancer, although the specific components of that diet that underly this increased risk are unknown.
Prostate Cancer Screening
Because there has been a lot of confusion surrounding prostate cancer screening tests, I felt like a section dedicated to the topic was warranted. There are currently two methods for screening for prostate cancer that are generally used in tandem:
- The prostate specific antigen (PSA) blood test, which detects elevated levels of the prostate-produced substance PSA in the bloodstream. A healthy prostate will generally (but not always) produce PSA levels between 4ng/ml of blood and 10ng/ml of blood. Men with PSA levels in this range have a 1-in-4 chance of harboring prostate cancer, while men with PSA levels above 10ng/ml have a greater than 1-in-2 chance of harboring prostate cancer. It is important to note that low PSA levels do not mean that a man is cancer-free; rather, approximately 15% of men with PSA levels below 4ng/ml are found to have prostate cancer on biopsy.
- The digital rectal exam (DRE), which is a physical examination in which the doctor manually inserts his fingers (or digits) into the rectum to directly check the prostate for changes that may be related to cancer. DREs are generally used to confirm or dispute PSA test results.
These tests have unequivocally been shown to find more prostate cancers, especially in the early stages of the disease, than would otherwise be diagnosed without regular screening, resulting in a significant decline in the death rate from prostate cancer since their implementation. So why is regular screening for prostate cancer not recommended for every man over the age of 40? Well, it’s complicated. Let’s try to sort through it all.
First and foremost, while the PSA and DRE tests are good at detecting cancer, the range of biological variability inherent in the prostate (and the levels of PSA produced by it) means that they can also be inaccurate. Some men have very low PSA levels even in the presence of cancer, resulting in false negative tests. Otherwise healthy men may have elevated PSA levels due to a host of other, non-cancer, conditions, resulting in false positive tests. And the DRE suffers from anatomical limitations, again resulting in a number of inaccurate test results. So while these screening tests can be useful, they are by no means ideal.
Moreover, as noted above, prostate cancer grows VERY slowly. Many otherwise healthy men are walking around with undiagnosed prostate cancer that due to its slow rate of progression, will never cause them medical problems during their lifetimes. Regular screening, then, leads to what many in the medical community consider to be an overdiagnosis of prostate cancer. While many of these men would likely opt to treat an asymptomatic cancer should they become aware of it, the reality is that a large portion of those treatments are medically unnecessary. Ultimately, there is a growing belief that because the side effects of treating prostate cancer can have a significant impact on a man’s quality of life (much more so than the cancer ever would!), the benefits of identifying and treating these cancers in their earliest stages are not sufficient to warrant those risks for the majority of men.
In May of 2012, the United States Preventive Services Task Force (USPSTF) updated their recommendations for prostate cancer screening. The USPSTF currently does not recommend PSA screening for any men, stating that there is “moderate or high certainty that the service has no benefit or that the harms outweigh the benefits”. You can read their full report here.
The Prostate Cancer Foundation strongly disagreed with the USPSTF recommendations, and summarized both their response to the USPSTF and their position on prostate cancer screening here. They also noted, in this synopsis of the prostate cancer screening debate, that, “in contrast [to the USPSTF], physician-led groups, such as the American Society of Clinical Oncology and the American Urological Association, maintain that PSA screening should be considered in the context of a man’s life expectancy and other medical conditions.” They further note that “most experts agree that there is no role for PSA screening for men expected to live less than 10 years”.
The official position of the American Cancer Society on prostate cancer screening is in agreement with the physician-led groups cited by the Prostate Cancer Foundation. Specifically, they state that:
At this time, the American Cancer Society recommends that men thinking about prostate cancer screening should make informed decisions based on the available information, discussion with their doctor, and their own views on the benefits and side effects of screening and treatment.
The ACS specifically recommends that men of average risk for developing prostate cancer and who otherwise have every reasonable expectation of living for at least another decade should discuss screening with their doctors starting at age 50. Men of above average risk (i.e. African American men, men with one first degree relative with prostate cancer) should start having these discussions at age 45 and men of high risk (that is, men with multiple first degree relatives with prostate cancer) should start having these discussion at age 40. For men who choose to undergo regular screening, the ACS recommends that men with PSA levels below 2.5ng/ml have follow up tests every two years while men with PSA levels above 2.5ng/ml should have follow up tests annually. Men should make decisions about biopsies and additional treatments based on marked and persistent changes in these test results in consultation with their doctors.
It is estimated that 241,740 men will be diagnosed with prostate cancer in 2012 and that 28,170 men will die from the disease. 99.2% of all men diagnosed with prostate cancer live at least five years following initial diagnosis, primarily due to the slow rate of progression of these cancers. One in six men will be diagnosed with prostate cancer at some point in their lifetimes and one in 36 men will die from the disease, making prostate cancer the most common non-skin cancer in men and the second leading cause of cancer death. The US spends an estimated $9.9 billion on treating prostate cancer annually. For comparison, the NCI allocated $300.5 million (or 5.9%) of their budget to prostate cancer research in 201o, the most recent year for which those statistics were available.
If you would like to learn more about prostate cancer, I highly recommend reading through the NCI’s web pages dedicated to prostate cancers, which can be found here. Their “snapshot” report on prostate cancer is particularly informative, especially the section discussing recent research investments and findings. I also found the American Cancer Society’s Learn About Cancer: Prostate Cancer section to be very useful. The Prostate Cancer Foundation’s section on prostate screening recommendations, which can be found here, summarizes this complicated topic very well. All of the statistics cited in the post were from the Surveillance Epidemiology and End Results (SEER) fact sheet on prostate cancer, which can be found here. These webpages were my primary sources of information for this blog post.
If you would like to read more about the current prostate cancer screening recommendations of the USPSTF, you can find that information here.
The American Association for Cancer Research also recommends the following prostate cancer advocacy and patient support organizations:
Finally, while they weren’t listed on the AACR website, I also recommend the Prostate Cancer Foundation for more information about prostate cancer in general and to learn how you can get more involved in advocating for prostate cancer research.
I hope that every reading this found this informative. I know I learned a lot researching it and will be a more effective cancer advocate for it!
Note: While I am a biomedical scientist, I am not considered an expert (medical or otherwise) on prostate cancer. This post, as with all of my “awareness month” posts, is not meant to be an in depth review of prostate cancer. Rather, I only wanted to provide a brief overview of prostate cancer in order to help further the larger cancer community’s awareness of this very common cancer. Moreover, while I provided links to a number of prostate cancer organizations at the end of this post, I have not researched these organizations to the extent that I do for my “Spotlight On” series of posts. Until I can research them further, I am not explicitly advocating financial donations to these organizations (although I certainly won’t advise you against it either should you find them worthy!). Instead, I am recommending them here because each organization is a well respected leader in these specific areas and is considered a reputable source for further information on prostate cancer.