New Molecular Cancer Test Needs Few Cells

A new test that looks for high levels of molecules embedded by methylation shows promise as a way to detect breast cancer in a tiny drop of body fluid containing relatively few cells. The results of preliminary tests were reported in the July 1, 2004, issue of Cancer Research.

The new method, called quantitative multiplex methylation-specific polymerase chain reaction (PCR), or QM-MSP, can detect cancer in a sample with as few as 50 cells. In the process, small methyl groups regulate DNA's message-manufacturing process by attaching to the "on” switch of genes. Abnormal levels of methylation then improperly turn the gene switch off, which leads to the loss of critical proteins found in normal cells and adds to the genetic events leading to cancer.

"Until now, accurate levels of methylation in many genes at the same time was impossible without repeated tests, and with a small sample, we didn't have enough DNA to perform all those tests,” explained first author Mary Jo Fackler, Ph.D., research associate at the Johns Hopkins Kimmel Cancer Center (Baltimore, MD, USA; www.hopkinsmedicine.org). "Now, we've taken two existing types of MSP tests and put them together, which minimizes the amount of sample needed.”

QM-MSP determines the percentage of methylation present in each of four to five breast cancer genes. The percentages are added together for a cumulative score, which is compared to a threshold value. Levels above the threshold indicate the potential presence of cancer cells and those below threshold suggest that the samples are normal.

In one set of experiments, the researchers tested QM-MSP on tissue samples, using a panel of genes whose abnormal methylation patterns are known to be associated with breast cancer. The test detected cancer in 84% (16 of 19) of breast tumor samples, and found no cancer in 89% (eight of nine) of normal tissues.

Then the researchers tested QM-MSP on breast duct fluid samples obtained by ductal lavage, a saline wash with a catheter threaded through the nipple. Of seven patients at high risk for breast cancer and no known cancer present, six had no detectable levels of abnormal methylation and one woman had low levels of abnormal methylation in one gene. QM-MSP detected cancer in two out of four breast cancer patients, which indicates that this type of assessment hold promise. It is now being evaluated in larger studies at Johns Hopkins.

The QM-MSP test could also be used for the analysis of methylation in other cancers, such as oral lavage in head and neck, or sputum for lung cancer, in which tissue samples are usually small, said the researchers. "Our goal is to add a molecular solution to problems in cancer diagnosis where the sample is not adequate or microscopic evaluation of cells is unclear,” explained Sara Sukumar, Ph.D., professor of oncology at the Kimmel Cancer Center. "If additional studies prove the feasibility of this test, it will provide molecular clues to cellular pathology and mammography findings that may help to decide whether cancer is present.”


Related Links:
Johns Hopkins Kimmel Cancer Center