Circulating tumor cells can reveal genetic signature of dangerous lung cancers

Jul 9 2008

Using a miniature laboratory-on-a-chip device, a team of investigators at the Massachusetts General Hospital, led by Daniel Haber, M.D., Ph.D., and Mehmet Toner, Ph.D., both members of the MIT-Harvard Center for Cancer Nanotechnology Excellence (CCNE), has developed a method that detects and analyzes the genetic signature of rare tumor cells in the bloodstream.

The results from this analysis allowed the researchers to identify those patients most likely to respond to a specific targeted treatment. This chip-based analysis also allowed the researchers to monitor genetic changes that occur during therapy.

According to Dr. Haber, this chip opens up a new field of studying tumors in real time. "When the device is ready for larger clinical trials, it should give us new options for measuring treatment response, defining prognostic and predictive measures, and studying the biology of blood-borne metastasis, which is the primary method by which cancer spreads and becomes lethal." Dr. Haber and his team published their results in The New England Journal of Medicine.

Circulating tumor cells (CTCs) are living solid-tumor cells found at extremely low levels in the bloodstream. Until the development of the CTC-chip by the Massachusetts Institute of Technology (MIT)-Harvard CCNE team, it was not possible to get information from CTCs that would be useful for clinical decision-making. The current study was designed to determine whether the device could go beyond detecting CTCs to helping analyze the genetic mutations that can make a tumor sensitive to treatment with targeted therapy drugs.

The researchers tested blood samples from patients with non-small-cell lung cancer (NSCLC), the leading cause of cancer death in the United States. In 2004, cancer researchers had discovered that mutations in a protein called epidermal growth factor receptor (EGFR) determine whether NSCLC tumors respond to a group of drugs called tyrosine kinase inhibitors (TKIs), which includes gefitinib (Iressa) and erlotinib (Tarceva). Although the response of sensitive tumors to those drugs can be swift and dramatic, eventually many tumors become resistant to the drugs and resume growing.

The CTC-chip was used to analyze blood samples from 27 patients-23 who had EGFR mutations and 4 who did not-and CTCs were identified in samples from all patients. Genetic analysis of CTCs from mutation-positive tumors detected those mutations 92 percent of the time. In addition to the primary mutation that leads to initial tumor development and TKI sensitivity, the CTC-chip also detected a secondary mutation associated with treatment resistance in some participants, including those whose tumors originally responded to treatment but later resumed growing.

Blood samples were taken at regular intervals during the course of treatment from four patients with mutation-positive tumors. In all of those patients, levels of CTCs dropped sharply after TKI treatment began and began rising when tumors resumed growing. In one patient, adding additional chemotherapy caused CTC levels to drop again as the tumor continued shrinking.

Throughout the course of therapy, the tumors' genetic makeup continued to evolve. Not only did the most common resistance mutation emerge in tumors where it was not initially present, but new activating mutations-the type that causes a tumor to develop in the first place-appeared in seven patients' tumors, indicating that these cancers are more genetically complex than expected and that continuing to monitor tumor genotype throughout the course of treatment may be crucial.

"If tumor genotypes don't remain static during therapy, it's essential to know exactly what you're treating at the time you are treating it," says Haber. "Biopsy samples taken at the time of diagnosis can never tell us about changes emerging during therapy or genotypic differences that may occur in different sites of the original tumor, but the CTC-chip offers the promise of noninvasive continuous monitoring."

This work, which was supported in part by the National Cancer Institute's Alliance for Nanotechnology in Cancer, is detailed in the paper "Detection of Mutations in EGFR in Circulating Lung-Cancer Cells." An abstract of this paper is available through PubMed. View abstract

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