Tumor DNA detected in blood samples.

2002 DEC 19 - (NewsRx.com & NewsRx.net) -- Scientists at Johns Hopkins have successfully detected ovarian cancer using a blood test for DNA shed by tumors.

The test is based on digital analysis of single nucleotide polymorphisms (SNP, or "snips"), in which investigators separate the two strands of code found in every gene to search for imbalances that are a hallmark of cancer cell DNA.

With 54 blood samples from late- and early-stage ovarian cancer patients, the Hopkins team used digital SNP analysis to find so-called "allelic imbalance" in 87% (13 out of 15) of early-stage ovarian cancers and 95% (37 out of 39) with late-stage disease. No allelic imbalance was detected in 31 blood samples from healthy individuals. The researchers also compared the type of allelic imbalance found in 17 of the samples with the corresponding tumor tissue and found that 15 of these had matching allelic imbalance patterns.

Details of the initial studies of the test are published in Journal of the National Cancer Institute.

"Digital SNP appears to detect ovarian cancers very well and is far more precise than other available tests," said Ie-Ming Shih, MD, PhD, pathologist and director of this study for the Kimmel Cancer Center at Johns Hopkins. But, Shih cautioned, digital SNP is too costly and labor intensive at present to serve as a general screening test. "Currently there still is no way to usefully screen all women for ovarian cancer," Shih said, although it might be useful for women at high risk.

The Hopkins group also is investigating ways of achieving the same accurate detection rate with a less costly, more efficient test that could be used on a broader scale for ovarian and a variety of other cancers, Shih said.

DNA released from dying cells has long been detectable in blood samples, using sensitive molecular technology. But to distinguish normal from cancerous DNA, Kimmel Cancer Center scientists analyzed both sets of genetic code in DNA sequences. The individual sets of code are called alleles. In normal cells, DNA's two alleles - one derived from the maternal copy of the gene and the other from the paternal copy - are balanced in their basic building blocks. Tumor cells, on ...