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Obesity increases men's risk of dying from prostate cancer

Men who are overweight are more likely to have precancerous lesions detected in a benign prostate biopsy and are at a greater risk for subsequently developing prostate cancer, a new study shows.

“It is absolutely clear that obesity increases a man’s risk of dying from prostate cancer,” said Dr. Andrew Rundle, associate professor of epidemiology at Columbia University’s Mailman School of Public Health in New York City, who conducted the study.

But, he told NBCNews.com, “We don’t know if obesity causes it (prostate cancer) or makes it harder to treat.” Rundle’s study was published on Tuesday in Cancer Epidemiology, Biomarkers & Prevention, a journal of the American Association for Cancer Research.

He noted that being overweight is known to cause five cancers -- post-menopausal breast, colon, kidney, endometrial (uterus) and esophageal. Cancer of the prostate -- the gland that releases the male hormone, testosterone, into the body -- is the leading diagnosed cancer in men and the second leading cancer killer of men behind lung cancer.

According to the American Cancer Society, 28,000 men died of it last year in the United States and over 238,000 new cases will be detected in the country this year.

"Studies conducted in the past have attempted to determine if there are subpopulations of men diagnosed with benign conditions that may be at a greater risk for developing prostate cancer,” Rundle said. “This is one of the first studies to assess the association between obesity and precancerous abnormalities."

Rundle and his colleagues studied obesity and future prostate cancer incidence in 6,692 men at the Henry Ford Health System who were followed for 14 years after a biopsy or transurethral resection of the prostate with benign findings. To determine obesity, he used the standard Body Mass Index, which factors in weight and height combined. Taking an average BMI of 30, Rundle said about one-third of the U.S population is considered obese.

The researchers conducted a case-control study among 494 of these patients and 494 matched controls; they found precancerous abnormalities in 11 percent of the patients' benign specimens. These abnormalities were significantly associated with obesity at the time of the procedure, according to Rundle.

After accounting for variables, including family history of prostate cancer, prostate-specific antigen (PSA) levels in the blood, and the number of PSA tests and digital rectal exams during follow-up, the researchers found that obesity at the time of the initial procedure was associated with a 57 percent increased incidence of prostate cancer during follow-up.

Generally, a biopsy will be performed after a high PSA level, or if a doctor can detect a hardening of the prostate during a digital rectal examination. The biopsy takes minute slivers of tissue from the gland to test for cancerous cells. But it can be inaccurate, depending on where the tissues are taken from, and can miss cancerous cells.

“It is possible that the tumors missed by initial biopsy grew and were detected in a follow-up biopsy," Rundle said.

Helena Furberg, associate attending epidemiologist at Memorial Sloane-Kettering Cancer Center in New York City, said Rundle's findings represented "a significant research study" at a time of controversy over whether obesity is associated with the risk of prostate cancer.

“Now, future studies should look at the question: does losing weight decrease the risk of prostate cancer?” she said in an interview with NBCNews.com.

Furberg also noted the study shows how the accuracy of a biopsy can be affected and fail to detect pre-cancerous lesions in obese patients who have a larger prostate. “In future, clinicians should take into consideration the size of the patients,” she said.

Dr. Marcus Quek, associate professor of urology at Loyola University Medical Center outside Chicago, said previous studies have come to conflicting conclusions about how obesity and prostate cancer may be related.

“This study tells us more work needs to be done on the link between obesity and cancer,” he said. “And if we find they are related, whether we can modify the risk.”

Quek noted Dr. Rundle’s study had found lesions during follow-ups, indicating that they had been missed in the initial biopsy.

“Biopsies are only so accurate,” Quek said. ”People have looked at ways to improve prostate biopsies, with MRI and other imaging technology.”

“But right now, they are only as accurate as where they put the needles.”