About half of early-stage hormone receptor-positive breast cancers stop responding to hormone therapy. These cancers can be compared to a room with a light switch. Initially, the breast cancer has just one light switch that you need to hit to turn off the lights. But as the breast cancer mutates, it grows an additional light switch, so now you must hit both at the same time if you want to kill the cell.
Almost all advanced-stage, hormone receptor-positive cancers eventually become resistant to hormone therapy. But by combining hormone therapy with a new class of drugs called mTOR inhibitors, doctors can hit both switches at once. The mTOR inhibitors act on proteins called kinases, slowing down the cancer's growth.
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