When breast cancer spread to the liver, a change in the biology of the cancer required a treatment switch for more than one out of every 10 women, according to research presented yesterday at the American Society of Clinical Oncology's annual meeting.Researchers compared biopsy data from primary breast tumors and liver metastases in 255 women with metastatic breast cancer to see whether the cancer's estrogen, progesterone, and HER2 receptor status--factors that help determine the correct course of treatment--remained the same. Estrogen receptor status changed--that is, the cancer switched from estrogen receptor-negative to estrogen receptor-positive, or vice versa--in 37 patients (14.5 percent). When changes in HER2 status and progesterone status were also determined, a total of 31 patients (12.1 percent) changed treatment to match the tumor's new biology."As we have a whole new generation of targeted drugs over the next decade ... it will be that much more necessary to obtain tissue, not just when a woman first has metastatic breast cancer, but potentially over the course of her illness because there is the potential that the cancer can evolve over time," said Eric Winer, MD, of Dana-Farber Cancer Institute in Boston, during a press briefing. Winer was not involved in the study. "The take-home message is the default position in a woman with metastatic breast cancer should be to perform a biopsy. It's really not performing a biopsy that should be an exception," Winer said.Melissa Weber is the former managing editor of CURE and is covering the annual meeting of the American Society of Clinical Oncology.