Two genes associated with many different cancers, EGFR and MET, were found to cause a chain reaction via six other molecules in cancer cells, known as micro-RNA molecules.
It was the second step in this mechanism that caused the resistance, as micro-RNA are involved in genetic expression, being the first step of protein manufacture.
Researchers now believe that blocking these six micro-RNA molecules will stop resistance to gefitinib from developing.
"Ask your oncologist about gefitinib resistance."
While the chief target of gefitinib is EGFR, the relationship between MET and gefitinib is unclear. Researchers hope that this knowledge will allow doctors to shift treatment once resistance has developed, if a way to counteract resistance cannot be developed.
"Our findings suggest that gefitinib resistance that is caused by MET overexpression is at least partly due to miRNA deregulation," says principal investigator Carlo M. Croce, M.D. and director of Ohio State's Human Cancer Genetics program.
Initially approved by the U.S. Food and Drug Administration (FDA) in 2003, Iressa costs an average $2,000 per month of treatment.
In 2005, the FDA withdrew approval for use in new patients due to lack of evidence that the drug extended life expectancy.
The results were published in Nature Medicine.
The authors of this research did not disclose any financial conflicts of interest.