CHICAGO (Reuters) - US researchers have found a way to pinpoint where in the prostate a tumor may be hiding by using an imaging technique that measures the chemical composition of tissues.

Although the research is in its early stages, the finding may lead to a better way for doctors to diagnose prostate cancer, they said on Wednesday.

A team at Massachusetts General Hospital in Boston used magnetic resonance spectroscopy, which analyzes the biochemistry rather than the structure of tissues

"It detects tumors that cannot be found with other imaging approaches and may give us information that can help determine the best course of treatment," said Leo Cheng of Mass General, whose study appears in the journal Science Translational Medicine.

Blood tests that screen for prostate-specific antigen or PSA can suggest cancer, but benign growths can generate excess PSA too and currently doctors have no imaging test that can confirm the size or location of tumors within the prostate, or tell how aggressive they might be.

Prostate biopsies are done "blind" and can easily miss a tumor.

Doctors have routinely recommended prostate cancer screening in men over 50 based on the assumption that early diagnosis and treatment is better than doing nothing.

But a study in August found that routine screening for prostate cancer resulted in more than one million US men being diagnosed with tumors who might otherwise have suffered no ill effects from them.

Standard forms of treatment — surgery, radiation or hormone therapy — can cause impotence and incontinence. But while many prostate cancers are slow-growing, some are deadly.

"The current imaging technology cannot see where the cancer is. Even when we found the cancer through biopsy, we do not know if it is aggressive or not," Cheng said in a telephone interview.

To address this, Cheng and colleagues turned to MR spectroscopy, which relies on different radio wave frequencies to measure the chemical composition of tissues. No contrast agent is needed.

"Different chemicals will appear at different wavelengths," he said.

In a prior study, Cheng's team used the scanner to analyze all the different metabolic pathways that are active in cancerous prostate glands.

"We found out that cancer tissue has a different chemical profile compared with normal tissue," he said.

They identified 36 critical metabolites that were active in prostate tumors that differed from a healthy prostate.

Using this profile, they developed a software program that compares the chemical information from the MR spectroscopy to the profile of a prostate tumor.

Then they scanned prostate glands that had been removed and were later dissected in the lab. They found the software was highly accurate at finding cancers within the tissue.

Cheng said his lab is trying to replicate the findings in a larger study, and they hope to develop more technology that can identify aggressive cancers from the slow-growing kind.

Currently, the work is done on a research scanner, but the team hopes to adapt it for scanners widely available in hospitals.

Prostate cancer is the second most common cancer in men worldwide after lung cancer, killing 254,000 men each year.