Previous research suggests that insulin may spur the growth of prostate cancer cells. In type II diabetes, the body fails to properly use insulin, which can lead to an excessive amount of insulin in the blood.

"We looked at several key pretreatment factors used to stage the prostate cancer," explained Khanh H. Nguyen, M.D., lead author of the Fox Chase study and a resident in the radiation oncology department at Fox Chase. "These factors include the initial PSA, Gleason score and T-stage. The men with type II diabetes didn't have a significantly different initial profile for their prostate cancer than the men without diabetes. Additionally, type II diabetes did not appear to influence the rates of PSA failures or distant metastases. However, men with type II diabetes had significantly worse long-term overall survival."

The patient cohort for this study included 1,512 men with localized prostate cancer treated with radiation therapy between April 1989 and October 2001. Of these, 1,306 men had no history of type II diabetes (NDM) while 206 men had diabetes (DM-II), which was managed with diet, exercise or medications other than insulin.

The study did not detect significant differences in the initial PSA, Gleason score, or T-stage between the men with and without diabetes. The median initial PSA for men with NDM was 8.2 compared to 8.7 for men with DM-II. Twenty-eight percent of NDM cases versus 26 percent of those with DM-II had a Gleason score of 7-10. By T-stage, 94 percent of NDM patients and 93 percent of DM-II patients had stage T1a-2c disease.

The researchers also looked at the effect of DM-II on long-term radiation treatment outcomes. At 5 years, 27.2 percent (355) of men with NDM had PSA failures versus 23.8 percent (49) of men with DM-II. Seven percent (92) of NDM patients had distant metastases compared to 4.9 percent (10) with DM-II.

Of the patients with NDM, 3.1 percent (41) died of prostate cancer versus 2.4 percent (5) of patient with DM-II. "Although men with type II diabetes did not have significantly different treatment outcomes, having the disease had a detrimental effect on overall survival," said Nguyen.

Of the men without diabetes, 19.1 percent (250) died from all causes, compared to 22.8 percent (47) deaths overall for those with DM-II. This result was statistically significant even after adjusting for the key pretreatment factors.

Nguyen, now a radiation oncologist at the University of Tennessee Medical Center in Knoxville, Tenn., concluded, "The degree of hyperinsulinemia in type II diabetes can vary considerably and may obscure the true impact of insulin on the natural history of prostate cancer. Despite laboratory and epidemiological data suggesting an effect of insulin on prostate cancer growth, in our patient cohort, diabetes did not appear to influence the aggressiveness of prostate cancer at presentation.

"However, type II diabetes conferred a significantly higher overall mortality. Aggressive management of diabetes with diet, exercise, and medications may improve the survival of cancer patients."

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