AstraZeneca Plc said on Thursday that the U.S. drug regulator will give a speedy review to its experimental breast cancer treatment, which could put the British drugmaker in direct competition with bigger rival Roche Holding AG. The U.S. Food and Drug Administration (FDA) accepted AstraZeneca's application and granted the treatment, trastuzumab deruxtecan, a priority review for the treatment of HER2-positive metastatic breast cancer, the drugmaker said. The London-listed company in March agreed to pay up to $6.9 billion to work with Japan's Daiichi Sankyo on the treatment, in a direct challenge to the world's biggest cancer drug maker Roche. The treatment, also known as DS-8201, targets the HER2 protein, a major trigger of uncontrolled cell growth in about 20% of breast cancer cases. It is an area where Roche has been a pioneer with its best-seller Herceptin. DS-8201 is part of a drug class called antibody-drug conjugates (ADC), which link powerful cell toxins to antibodies that cling to cancer cells, sparing the healthy cells that are damaged during conventional chemotherapy treatments.