Prostate cancer patients who are obese or who have small prostates seem to have more aggressive tumors, study suggests.

The studies support earlier findings that obese men have a higher risk of getting prostate cancer in the first place - but take them a step forward to say such men may also be prone to more dangerous tumors.

“One consensus that seems to be evolving is that obese men have an increased risk of more aggressive, and therefore potentially more deadly, disease,” said Dr. Martha Terris, a urologist at the Veterans Affairs Medical Center in Augusta and the Medical College of Georgia who led the study.

“The take-home message for men and for all of us really is that we should try to maintain a healthy weight for a variety of health reasons,” she added in a statement.

Prostate cancer is the third most common cancer worldwide among men. The American Cancer Society says it will be diagnosed in 200,000 men in the United States alone this year and will kill 30,000.

It is often a slow-growing cancer that can be simply watched without treatment. But in some cases, it is aggressive and can spread quickly through the body. Doctors are trying to find the best ways to predict which men need quick treatment and which men can wait a while.

A blood test for a protein called prostate specific antigen or PSA can help, but PSA is produced by both healthy and cancerous prostate cells and a low PSA reading does not necessarily mean a man is free of cancer.

Obesity may interfere with early cancer diagnosis, Terris said, because it may be more difficult to examine obese men using a test called a digital rectal exam. This exam involves physically feeling the prostate with a finger.

Also, fat cells produce estrogen-like compounds, which in turn may interfere with circulating levels of PSA - giving men a seemingly all-clear PSA reading when in fact they have a tumor.

That could give the cancer a chance to spread and grow before it is detected, Terris was scheduled to tell a meeting of the American Urological Association in San Antonio, Texas.

Her team studied 787 men who had biopsies for suspected prostate cancer at a Veterans Affairs hospital in California between 1998 and 2002. Obese men were more likely to have a positive biopsy - one that showed cancer. In particular, younger, obese men had a higher risk. Obese men also had more aggressive tumors.

Terris also examined the cases of more than 1,000 men taking part in another Prostate cancer study.

“Men with smaller prostates tend to have smaller cancers than men with larger prostates. But this is not as good as it sounds,” Terris said.

“If you have a large prostate, cancer can grow to a fairly large size before it outgrows the surrounding prostate and spreads out into other areas of the body. However, if the prostate containing the cancer is small, the cancer does not have to grow very much before it is big enough to spread outside the gland.”