A collaborative clinical trial will be put in place to evaluate the combination of Bristol-Myers Squibb’s immunotherapy Opdivo (nivolumab) and Daiichi Sankyo’s investigational antibody drug conjugate DS-8201 in HER2-expressing metastatic breast and urothelial (bladder) cancers. The Phase 1b multicenter, open-label study will include two parts. The dose escalation part will determine a possible recommended dose of DS-8201 in combination with nivolumab in patients with HER2-expressing breast cancer who are refractory to standard therapies or for which no standard therapy is available. The dose expansion part of the study will evaluate the efficacy, safety and tolerability of combining nivolumab with DS-8201 at the established dose level in patients with HER2-expressing advanced/metastatic breast cancer as well as HER2-expressing urothelial (bladder) cancer in patients previously treated with chemotherapy.