Weight and Screening for Prostate Cancer
The prostate is a gland of the male reproductive system. It produces some of the fluid that transports sperm during ejaculation. An estimated one in six men in the U.S. will be diagnosed with prostate cancer within his lifetime. Prostate cancer occurs more frequently in older men, in African-American men, and in men with a family history of prostate cancer.
Screening for prostate cancer includes prostate-specific antigen (PSA) testing for early detection of prostate cancer in men 50 years of age or older. PSA test measures proteins that are produced and shed by the prostate. PSA levels tend to be elevated when prostate cancer is present, but levels can also be elevated in benign (non-cancerous) conditions affecting the prostate. If a patient has elevated PSA levels, he often undergoes a biopsy, where tissue from the prostate is removed. The tissue samples are evaluated in the laboratory for the presence of cancerous cells. If PSA levels are normal, or even in the high range of normal, biopsies are not routinely performed.
Weight may be a factor in prostate cancer diagnosis because some studies have suggested that PSA levels may be influenced by body weight; specifically, lower PSA values have been observed in obese men. If this proves to be the case, it’s possible that elevated PSA levels could be masked in obese men, which means that a PSA test could fail to detect a present cancer. It may therefore be important to account for body weight when interpreting PSA test results. It’s also possible that the level of PSA that raises suspicion of prostate cancer may need to be shifted downward for obese men.
To further assess the relationships between body size, blood volume, and PSA level, researchers conducted a study among more than 13,000 men who underwent radical prostatectomy for prostate cancer.
Weight was assessed using the body mass index (BMI). BMI involves a comparison of weight to height (weight in kilograms divided by height in meters squared). A BMI between 18.5 and 24.9 is generally considered healthy, a BMI between 25 and 29.9 is considered overweight, and a BMI of 30 or higher is considered obese. The study assessed PSA concentration (measured as nanograms of PSA per milliliter of blood), as well as the total amount of PSA in circulation (measured as micrograms of PSA).
- Men with higher BMI tended to have greater blood volume and lower preoperative PSA concentration. The total amount of PSA in circulation, however, did not vary significantly by body weight.
- These results support the idea that PSA is diluted by the greater blood volume of obese men, resulting in a lower PSA concentration in spite of a similar total amount of PSA in circulation.
- The researchers note that these results will need to be confirmed in prospective studies of men without prostate cancer.
Weight and Prostate Cancer Survival
Excess body weight has also been linked to worse survival in patients with some cancers. To assess the relationship between weight and prostate cancer survival, researchers evaluated information from a previously conducted prostate cancer clinical trial.
The study enrolled 945 men with prostate cancer that had extended through the prostate capsule (T3) or that involved nearby lymph nodes. Study participants were treated with radiation therapy with or without Zoladex® (goserelin).
Information about BMI was available for 788 of the 945 study participants. Based on BMI, 31% of subjects were classified as normal weight, 51% were classified as overweight, and 18% were classified as obese.
- Five-year risk of death from prostate cancer was 6.5% among men with a BMI less than 25, 13.1% among men with a BMI between 25 and 29.9, and 12.2% among men with a BMI of 30 or higher.
- There was no significant relationship between BMI and death from causes other than prostate cancer.
The researchers conclude that among men with locally advanced prostate cancer, higher BMI is linked with a higher risk of death from prostate cancer. The researchers note that additional studies will be necessary to determine the reason for this link and to explore whether weight loss after a prostate cancer diagnosis influences survival.
Exercise and Hormone Therapy
A common type of treatment for patients with prostate cancer is referred to as hormone therapy, or androgen deprivation therapy (ADT). Because prostate cancer is stimulated to grow from exposure to male hormones, particularly testosterone, blocking or reducing exposure of cancer cells to these male hormones can reduce or prevent cancer growth. ADT, however, carries the risk of loss of bone mass. Exercise may be one way for patients undergoing treatment with ADT to maintain their bone density.
ADT reduces the amount of testosterone in the body, which ultimately reduces of prevents the growth of prostate cancer cells. However, ADT is associated with some significant side effects. One such side effect is loss of bone density or bone mass. Bone loss increases the risk of osteoporosis, bone fracture, pain, hospitalization, and immobility and requires increased medical costs. Therefore, many physicians recommend calcium supplementation and bone density scans prior to and during therapy with ADT.
Exercise also plays a role in varying aspects of cancer, with much research focused on its effects on patients already diagnosed with cancer. Because it is known that exercise can improve fatigue levels as well as bone density, researchers from Johns Hopkins University recently conducted a clinical trial to evaluate effects of exercise on fatigue levels among men with prostate cancer who underwent treatment with ADT. Bone density was also measured. This trial included 70 men with early prostate cancer who were scheduled to undergo radiation therapy; half of these patients were also scheduled to receive ADT. At initiation of the trial, these men were considered to have sedentary lifestyle. Half the men were instructed to begin exercising with just 20- to 30-minute walks during the week. The remaining half was instructed to continue their sedentary lifestyles.
- The men who exercised and received ADT actually experienced an increase in their bone mass (0.48% increase).
- Men who did not exercise and received ADT had a 2.14% decrease in their bone mass.
The researchers concluded that exercise prevents the loss of bone mass among men with prostate cancer who are being treated with ADT.
As evidence mounts, the fact that that exercise and weight can play major roles in the diagnoses and outcomes of various types of cancers, including prostate cancer, continues to be reinforced.
 Reference: Bañez LL, Hamilton RJ, Partin AW et al. Obesity-related plasma hemodilution and PSA concentration among men with prostate cancer. Journal of the American Medical Association. 2007;298:2275-2280.
 Reference: Efstathiou JA, Bae K, Shipley WU et al. Obesity and mortality in men with locally advanced prostate cancer. Analysis of RTOG 85-31. Cancer [early online publication]. November 12, 2007.
 Reference: Chiplis P, et al. Effects of exercise on bone loss and functional capacity during prostate cancer treatment. InternationalJournal of Radiation Oncology, Biology and Physics. 2007;69:supplement S (S321-322).