October 10, 1994
Media Contact:Karin Twilde
Phone: (410) 955-1287
Researchers at the Johns Hopkins Oncology Center and Department of Otolaryngology have developed a diagnostic test for cancer that holds promise as a broad-based screening tool. Testing may begin within the year.
The findings are reported in the October 11 issue of the Proceedings of the National Academy of Sciences.
The test identifies replication errors in DNA that occur frequently in cancer. The test uses these errors, called clonal markers, as a fingerprint for cancer. The researchers compare these markers obtained from several cancer types with cells found in tissue, body fluids or secretions from the suspected cancer site (for example, urine from patients suspected of having bladder cancer). Matching markers, if found, indicate that malignant (clonal) cells are present in the tissue or fluids and the patient has cancer.
"Clonal markers are a definitive indicator of cancer. If you see these markers, you know you've found disease," says David Sidransky, M.D., professor of oncology and otolaryngology and principal investigator of this study.
Sidransky and his team used a technique known as polymerase chain reaction, or PCR, to amplify and detect several of these markers in primary human cancers. They then used the same method to look for matching clonal markers in samples, including urine, sputum, and surgically removed tissue, from five patients with symptoms of cancer. They detected cancer cells in all of the samples examined.
The clonal markers identified in this study are actually junk pieces of repetitive DNA. In healthy people, these errors usually are repaired quickly in the DNA replication process and go undetected. In cancer, however, they occur in cells along with genetic mutations that cause uncontrolled cell growth. As a result, all cancer cells carry the genetic mutations along with their clonal markers. The clonal markers are not actually involved in the development or progression of the disease but are a "red flag" for cancer cells.
Scientists estimate that there are nearly 100,000 pieces of repetitive DNA potentially useful as clonal markers throughout the human genome. Several thousand already have been identified. Sidransky currently is comparing these known markers against specific cancers to identify approximately 10-20 for use as a general test for cancer.
Initial testing may begin within the year in people at high risk for bladder and cervical cancers. However, Sidransky anticipates future testing for other cancers, including lung, head and neck, breast, colon and prostate. He believes the test, expected to cost about $50, may become part of routine medical care, providing a simple method of detecting cancer early, in its most treatable stages.
Other participants in the research are Li Mao, M.D., Daniel J. Lee, M.D., Melvyn S. Tockman, M.D., Yener S. Erozan, M.D., and Frederic Askin, M.D.
Funding for this study was provided by a National Cancer Institute lung cancer SPORE (Specialized Programs of Research Excellence) grant and by Oncor Inc. of Gaithersburg, Md. Under an agreement between Oncor and the Johns Hopkins University, Sidransky is entitled to a share of sales royalty received by the University from Oncor. Under that agreement, the University and Sidransky also have received Oncor stock which, under University policy, cannot be traded until products related to this research are sold. The terms of this arrangement have been reviewed and approved by the University in accordance with its conflict of interest policies.