PHILADELPHIA (October 18, 2015) — Prostate cancer is the second most common cancer found in men in the United States, affecting 14 percent, whereas diabetes affects about 9 percent of the population. Even though both conditions are often present in the same individual, it has not been clear how a diabetes diagnosis affects clinical outcomes for prostate cancer. Research at Fox Chase Cancer Center – Temple Health showed that the answer depends on what type of anti-diabetic drugs, if any, prostate cancer patients are taking.
By examining a large database of prostate cancer patients, the researchers found that diabetic individuals who either took insulin or did not take any anti-diabetic medications had lower survival rates and worse adverse effects from radiation therapy compared with non-diabetic patients. The findings were presented October 18 at the 57th Annual Meeting of the American Society for Radiation Oncology (ASTRO) in San Antonio, Texas.
“The implication of the study is that prevention and control of diabetes is important, particularly among cancer patients,” said lead study investigator Nicholas G. Zaorsky, MD, resident physician in radiation oncology at Fox Chase. “Men who are having their prostate cancer treated should be mindful of any other conditions they have been diagnosed with, and they should continue to see physicians who will manage these conditions appropriately.”
To examine the link between diabetes and prostate cancer, Zaorsky and his collaborators reviewed their prospectively collected institutional database of 3,176 men undergoing intensity-modulated radiation therapy (IMRT) for localized prostate cancer. They then compared the outcomes of the 2,576 patients without a history of type 2 diabetes and the 600 patients with a history of type 2 diabetes.
Diabetic patients who were either taking insulin or not taking any anti-diabetic medication had a lower five-year survival rate, with a 200 percent increased risk of death as well as a higher risk of radiation-related adverse effects, compared with individuals who did not have type 2 diabetes. Moreover, men who did not take any medication to treat their diabetes also showed an increased risk of cancer-related death. “We were not surprised that patients with diabetes died of non-cancer causes more so than patients without diabetes,” Zaorsky said. “However, we were surprised to see that a diagnosis of diabetes causes these patients to be at a higher risk to die from prostate cancer itself.”
Although the underlying molecular mechanisms are unclear at this point, the researchers suggested that high blood sugar, insulin, and metformin may activate cancer-related signaling pathways to cause tumors to grow or resist therapy, leading to poor outcomes. “We hope that more basic science research is performed to explore the interplay among diabetes, anti-diabetes medications, and cancer,” Zaorsky said. “More detailed information about patient diet and other lifestyle choices as they relate to diabetes could shed light on this question.”
In future studies, Zaorsky and his collaborators will examine how diabetes influences the adverse effects of radiation treatment. They will also explore other medical conditions that increase the risk of death in prostate cancer patients. In the meantime, Zaorsky hopes that this study will increase awareness of the interplay between diabetes and cancer.
“When patients are diagnosed with cancer, they sometimes put the management of other diseases like diabetes on the backburner, and these patients may believe that the diagnosis of cancer gives them a free pass to live a less healthy lifestyle,” Zaorsky said. “Instead, we recommend that these patients have their cancer treated and actively manage their other conditions, from diet, to exercise, to appropriate medications. Patients with cancer and diabetes should work closely with other physicians, including primary care doctors and endocrinologists, to optimize their health.”