Widely occurring growth protein linked to prostate cancer

January 22, 1998
Web posted at: 8:37 p.m. EST (0137 GMT)

WASHINGTON (AP) -- A quarter of men have high levels of a growth protein linked to a greater likelihood of prostate cancer, according to a new study that may point scientists toward ways to reduce the incidence of the cancer.

Dr. Michael Pollak of McGill University, who co-authored the study with Harvard University scientists, said that if the new research is confirmed, doctors may one day use the protein to predict better which men will one day get cancer.

It's too early for men to seek testing for the protein, called IGF-1, Pollak said, but he has begun animal studies to test whether drugs that lower its level could prevent men from getting the disease.

"This research finding was a big surprise," Pollak said. "It opens up a whole new direction of research."

The study, published in Friday's edition of the journal Science, also raised a red flag for men who take growth hormone to fight the effects of aging: That still-experimental trend, hyped on the Internet, may raise their risk of prostate cancer because the growth hormone increases IGF-1 levels.

'Intriguing study'

Taking growth hormone "is, on the basis of our data, a risky business," Pollak warned.

The study "certainly is intriguing," said Dr. Otis Brawley, a prostate cancer expert at the National Cancer Institute.

An IGF-1 link to prostate cancer makes sense, because doctors have long advised people to lose weight to lower the risk of various cancers -- and overeaters have high IGF-1 levels, Brawley said.

Preliminary evidence also has been found that IGF-1 spurs prostate tumors to be more aggressive, a link Brawley wants studied quickly. If confirmed, it could shed light on why black men die of prostate cancer more than whites -- because blacks typically have higher IGF-1 levels, he said.

An estimated 184,500 American men will get prostate cancer this year, and about 39,000 will die, the American Cancer Society estimates. Aging men today often are screened for high blood levels of prostate specific antigen, or PSA, which can signal cancer.

But the test doesn't predict who will get cancer in the future, so doctors are seeking better "markers" that would act much as cholesterol does in predicting future heart disease.

In test tubes, IGF-1 -- insulin-like growth factor-1 -- stimulates growth of both cancer cells and normal prostate cells. So Harvard checked blood samples from its massive Physicians Health Study, which has followed men's health since 1982, for IGF-1 levels in 152 men who later got prostate cancer and 152 healthy "control" men.

Men with the highest IGF-1 were 4.3 times more likely to have been diagnosed with prostate cancer than men with the lowest levels, said lead researcher June Chan, a Harvard graduate student.

IGF-1 was a powerful cancer predictor regardless of the men's PSA test scores, Chan said. That suggests that combining PSA and IGF testing might pinpoint the men at highest risk years before cancer strikes, so it could be caught extra early.

'Hot lead'

But detecting prostate cancer early is controversial. Because nobody knows which side effect-ridden treatment works best, many men aren't treated, and there's no proof early detection actually saves lives, Brawley said.

So it's more important to follow up whether IGF-1 makes tumors more aggressive -- so doctors would know who needs more treatment -- and if lowering levels could prevent cancer, Pollak said.

IGF-1 cannot be eliminated, he stressed. It's necessary for a variety of bodily functions, so he is focusing on lowering abnormally high levels.

IGF-lowering drugs already are used to treat a very rare condition in which super-high IGF spurs children to grow into giants. Pollak is giving those drugs to mice prone to prostate cancer. If they protect the mice, he would test men and check how early in life the treatment would have to start.

He's also hunting for IGF-1 in other cancers and has some evidence it may affect breast cancer, too.

"No one would have thought of this 10 years ago," Pollak said. "It's a hot lead."

Copyright 1998   The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.

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