A new blood test for peptides cleaved by carboxypeptidase N may soon be available to help detect early stages of breast cancer.

Carboxypeptidase N, an enzyme that modifies proteins to produce smaller peptides, is elevated in lung cancer. A new study in Clinical Chemistry (2013; doi:10.1373/clinchem.2013.211953) showed that enzyme levels are also increased in breast cancer patients. Further, peptide levels in the blood accurately predicted the presence of early-stage breast cancer tissue in mice as well as a small population of human patients. 

“In this paper we link the catalytic activity of carboxypeptidase N to tumor progression in clinical samples from breast cancer patients and a breast cancer animal model,” said project leader Tony Hu, PhD, a biomedical engineer in the Department of Nanomedicine at Methodist Hospital Research Institute, Houston, Texas. “Our results indicate that circulating peptides generated by carboxypeptidase N can serve as clear signatures of early disease onset and progression.”

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Currently, there are no quick and inexpensive laboratory tests for the detection of breast cancer. The American Cancer Society recommends that healthy women age 40 years and older have a mammogram every year, and that healthy women younger than 40 years have a clinical breast exam every 3 years for breast cancer screening.

“We are trying to create a noninvasive test that profiles what’s going on at a tissue site without having to do a biopsy or costly imaging,” Hu said. “…This could be better for patients and a lot cheaper than the technology that exists…[the] materials only cost about $10 per test.”

Hu’s group has developed a method that combines nanotechnology and advanced mass spectrometry to separate and detect extremely low levels of peptides in the blood. They found that six carboxypeptidase N peptides occurred at high levels in the blood of patients with stage I breast cancer. These same six peptides also occurred at high levels in the blood of mice just 2 weeks after implantation of breast cancer tissue. In mice, blood levels of the peptides declined over the 8-week study period, suggesting that the test may be better at detecting early stages of breast cancer. Clinical trials of the test will begin in early 2014.

“…We suspect the activity of different enzymes goes up and down as the disease progresses. We will be looking at how we might add known and future biomarkers to the blood test to increase its robustness and accuracy,” Hu said.