CANCER FED BY TELLTALE SUBSTANCE : SCIENTISTS PERFECTING WAY TO DETECT TUMORS BY PROTEIN.

Byline: Daniel Q. Hanley Associated Press 

Scientists are developing what could prove to be a highly accurate way of finding cancer hidden in the body: detecting the presence of a protein that makes tumors live forever.

The protein, called telomerase, is the body's immortality chemical. Ordinarily it disappears after the fetus develops in the womb. But cancer cells produce this substance so they can divide over and over without succumbing to normal aging and death.

About 150 reports on telomerase are being presented at this week's meeting of the American Association for Cancer Research, up from five or so two years ago.

Researchers described how they are using telomerase to find cancers early, to distinguish them from benign growths, to judge cancer's lethal potency and to measure its recurrence after treatment.

One study found that telomerase appears to be even more accurate than examining cells under the microscope, now the standard way of judging whether they are cancerous.

Furthermore, at least a dozen pharmaceutical companies are working on drugs to shut down telomerase, starving cancer of something critical to its survival. None of these has entered human testing yet.

``This is one of the most exciting advances in cancer biology to emerge in the last decade,'' Dr. Jerry W. Shay of the University of Texas Southwestern Medical Center at Dallas said Tuesday.

However, it is unclear how far away a practical and reliable test may be.

Dr. Donald S. Coffey of Johns Hopkins University called the telomerase research ``a very interesting breakthrough'' but cautioned that it must be detected in cancer cells themselves, which are relatively inaccessible and means it cannot be offered as a simple blood test. He said current versions of telomerase tests are also probably not as accurate as they will need to be.

In adults, only cancer cells routinely make telomerase, and it can be detected in about 85 percent of tumors. In some major cancer killers, such as lung and breast cancer, telomerase production is turned on even before the cancers begin their dangerous spread.

Over the past two years, a test has emerged that can detect telomerase in samples that contain as few as 10 cancer cells.

Cancers produce many kinds of chemicals. However, most are also found in normal tissue, too, so they cannot serve as an accurate signpost of malignancy. Experts hope that telomerase's unique role in cancer will make it a useful marker for many different kinds.

Shay and colleagues measured telomerase levels in nervous system tumors called meningiomas that were removed surgically. They found that the cancer recurred within three years in three of five patients whose tumors had telomerase but in none of the 25 whose tumors did not have this chemical.

At Hiroshima University in Japan, Dr. Eiso Hiyama is exploring the use of telomerase to detect whether patients have pancreatic cancer, a malignancy that is notoriously difficult to find before it has spread.

Tubes called endoscopes can be used to remove tissue samples from ducts inside the pancreas when cancer is suspected. He found that 12 of 13 patients whose tissue showed signs of telomerase turned out to have cancer. However, 18 others with no evidence of telomerase appeared to be cancer free.

``These findings suggest that telomerase activity in cells derived from pancreatic ducts may be a useful marker in the diagnosis of pancreatic cancer,'' Hiyama said.

In another study, Dr. Louis Dubeau of the Kenneth Norris Jr. Comprehensive Cancer Center in Los Angeles used telomerase to monitor patients treated for ovarian cancer, a hard-to-treat cancer that often spreads throughout the abdominal cavity.

After surgery and chemotherapy, doctors typically perform a second major operation to scan the abdomen for signs of cancer. Dubeau said looking for telomerase instead may eliminate the need for this operation.