Can a new breast cancer drug work in just days? Study shows it quickly reduces tumor fuel and slows growth.

For women with the most common type of breast cancer, the cancer cells are often fueled by the hormone estrogen. A new drug called camizestrant is designed to block and break down the estrogen receptor, which is like cutting off the tumor's fuel supply. In this short study, women took the drug for either about a week or about two weeks before their scheduled surgery. The results were promising. The drug reduced levels of the estrogen receptor in the tumor by about 65% after just 5-7 days, and this happened with all three doses tested. The drug also slowed cancer cell growth, measured by a marker called Ki67, and this effect was stronger after taking the drug for 12-15 days. Importantly, the lowest dose (75 mg) worked just as well as the higher doses at reducing the estrogen receptor and slowing growth. At this lowest dose, most women reported no side effects from the drug, and any that did occur were mild. The study concludes that the 75 mg dose is well-tolerated and achieves the maximum effect on the tumor, supporting its use in larger, long-term trials to see if it helps patients live longer or better.