TORONTO, Canada--Understanding why normal cells grow old and die while cancer cells do not could be a boon to cancer research (see drawing on page 1). US and Canadian scientists have discovered that a protein called telo-merase may be the cause of the "eternal youth" of cancer cells, and they are seeking to develop drugs to block its effects.
Researchers have found that significant levels of telomerase are present in as many as 95% of all malignant cancer cells in humans, but not in normal tissues, with the exception of reproductive cells from ovaries or testes.
In a presentation at the American Association for Cancer Research meeting, Jerry W. Shay, PhD, a cell biologist at the University of Texas Southwestern Medical Center at Dallas, said that telomerase may be the substance that gives cancer cells their immortality, and if there is no telomerase activity in tumors, those tumors may spontaneously regress.
In his study on neuroblastoma tumors, the most common solid tumor found in children under the age of 5, Dr. Shay and his team found telomerase in 94 of 100 tumors.
The tumors with high levels of telomerase activity also had other genetic changes and an unfavorable prognosis. The tumors with low telomerase activity did not have genetic mutations and were associated with a favorable prognosis.
Three of the neuroblastoma tumors that did not show telomerase activity were from a type of tumor that often spontaneously regresses in children.
The investigators made similar observations in small-cell lung cancer, with 100% of samples studied testing positive for telomerase. In contrast, only about 80% of 136 non-small-cell lung cancers expressed telomerase, Dr. Shay said. "This may explain why so many more non-small-cell lung cancer patients respond well to treatment."