MONDAY, April 13 (HealthDay News) -- A specialized technique that can detect subtle changes in cancer cells contained in a drop of blood or a tiny piece of tissue may one day be used by doctors to better assess how cancers are responding to treatment, say U.S. researchers.

"Currently, we don't know what's going on in a patient's actual tumor cells when a treatment is given. The standard way we measure if a treatment is working is to wait several weeks to see if the tumor mass shrinks. It would really be a leap forward if we could detect what is happening at the cellular level," lead author Dr. Alice Fan, a clinical instructor in the oncology division at the Stanford University School of Medicine in California, said in a school news release.

"This technology allows us to analyze cancer-associated proteins on a very small scale," senior study author Dr. Dean Felsher, an associate professor of medicine and of pathology, said in the news release. "Not only can we detect picogram levels -- one-trillionth of a gram -- of protein, but we can also see very subtle changes in the ways the protein is modified."

Variations in the way a protein is modified can affect how it functions in tumor progression. Cancer cells can dodge common therapies by changing their levels of protein expression and degrees of modification, according to background information in the news release.

The ability to continuously analyze small samples from cancer patients undergoing treatment may help doctors identify "rogue" cells before they can create a more treatment-resistant tumor. This technology could also help identify patients with cancers that are resistant to standard treatments.

Tests showed the technique was effective in samples of blood cancers, and the researchers hope it will also help track solid tumors. The Stanford team collaborated with researchers from Cell Biosciences, which makes the machine used in the study.

The study is in the April 12 online issue of the journal Nature Medicine.

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