Syndax Pharmaceuticals Inc., of Waltham, Mass., is collaborating with Genentech Inc., of South San Francisco, a unit of Roche Holding AG, to test Syndax's entinostat, a class I HDAC inhibitor, with Genentech's programmed cell death ligand 1 blocking antibody Tecentriq (atezolizumab) in patients with second-line hormone receptor positive, human epidermal growth factor receptor 2 negative metastatic breast cancer.