ZURICH, March 8 (Reuters) - Roche won U.S. approval on Friday of its immunotherapy Tecentriq to treat a significant number of patients with triple-negative breast cancer, a development hailed by doctors as a promising advance in fighting the aggressive disease. The U.S. Food and Drug Administration (FDA) approved Tecentriq mixed with the chemotherapy Abraxane to treat inoperable, locally advanced or metastatic triple-negative breast cancer (TNBC) in people whose tumours express PD-L1, a protein that may help cancers avoid detection by the immune system.