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After radical prostatectomy, the combination of diabetes and obesity seems to boost the risk of metastasis four-fold, new research suggests.
"Diabetes by itself does not seem to increase the risk of prostate cancer metastasis," Dr Stephen J. Freedland from Duke University School of Medicine, Durham, North Carolina told Reuters Health. "But diabetes and obesity somehow interact to increase prostate cancer aggressiveness."
His team had previously reported that obesity modified the effect of diabetes on prostate cancer aggressiveness, leading to a 2.52-fold increased risk of biochemical recurrence in obese white men.
How the study was done
In this study, published January 10th online in BJU International, they sought to determine if diabetes influences the time to metastasis, a more definitive clinical endpoint than biochemical recurrence.
Using registry data on 2 058 men who had radical prostatectomy, they found that 379 (18%) had diabetes at the time of their surgery.
Overall, diabetes was not significantly associated with metastasis risk, even after adjusting for multiple characteristics in both pre- and postoperative models and after stratifying by race.
When stratified by obesity, however, metastasis risk was 3.98 times higher in men with diabetes and obesity - but not in nonobese diabetics, who instead showed a trend toward a lower metastasis risk.
Longer duration of diabetes was also significantly related to increased metastasis risk.
The formal test of interaction between diabetes and obesity was also significant, the researchers note, suggesting synergy between these two disorders.
Moreover, in obese men, there was a near-significant association between diabetes and higher secondary treatment rates, whereas in nonobese men, diabetes was associated with significantly lower treatment rates.
What the findings mean
"So less aggressive therapy does not account for the higher risk of metastasis in obese men with diabetes," Dr. Freedland said, "but we're not sure why this is the case."
Dr. Freedland said stored serum is available for other large cohorts of men and he hopes metabolomics and other tests can help clarify this interaction between diabetes and obesity.
"In the meantime," he said, "it makes sense to address obesity with exercise and diet in an effort to mitigate the risk of metastasis in these men."
Dr. Freedland and his colleagues also plan to investigate whether diabetes and obesity interact to increase the risk of developing aggressive prostate cancer in the first place.
Registry data for this study came from the Shared Equal-Access Regional Cancer Hospital database. The research was supported in part by an American Urological Association Foundation/Astellas Rising Star in Urology Award to Dr. Freedland, and by a Howard Hughes Medical Institute Medical Research Fellows scholarship to one of his coauthors.
(Reuters Health, January 2013)
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