WEDNESDAY, March 23 (HealthDay News) -- A new study helps explain how some lung cancers become resistant to targeted drug therapy.

Researchers at the Massachusetts General Hospital Cancer Center analyzed tumor samples from 37 patients with non-small cell lung cancer, the leading cause of cancer death worldwide, and identified two new genetic changes associated with resistance.

They also confirmed resistance-related genetic changes identified in previous studies.

The MGH team also discovered that the cellular nature of some tumors changes in response to treatment and that genetic mutations associated with drug resistance can disappear after treatment is halted.

The findings highlight the importance of monitoring the molecular status of lung cancer tumors throughout the treatment process, the researchers said.

"It is really remarkable how much we oncologists assume about a tumor based on a single biopsy taken at one time, usually the time of diagnosis," lead author Dr. Lecia Sequist said in an MGH news release. "Many cancers can evolve in response to exposure to different therapies over time, and we may be blind to the implications of these changes simply because we haven't been looking for them."

"Our findings suggest that, when feasible, oncogene-driven cancers should be interrogated with repeat biopsies throughout the course of the disease," Sequist said. "Doing so could both contribute to greater understanding of acquired resistance and give caregivers better information about whether resumption of targeted therapy or initiation of a standard therapy would be most appropriate for an individual patient."

The study appears March 23 in the journal Science Translational Medicine.

More information

The American Cancer Society has more about non-small-cell lung cancer.