By Natalie Grover LONDON (Reuters) – AstraZeneca and Daiichi Sankyo’s Enhertu extended survival by more than six months in patients with a form of advanced breast cancer compared to standard chemotherapy, according to data presented on Sunday. The data, unveiled at the American Society of Clinical Oncology (ASCO) meeting in Chicago, could open a large, new multibillion-dollar patient population for the drug that won U.S. approval in late 2019 as a third-line treatment for the 15% of breast cancer patients with HER2-positive disease. The ongoing phase III trial involves over 550 patients with s…