The selloff of Puma Biotechnology is an overreaction, said RBC Capital Markets' Michael Yee on Monday.
Puma's stock fell 13 percent to $169.97 on Monday. Investors were reacting to the release of phase three clinical trial data for the company's breast cancer drug, he said.
Yee, who is attending the American Society of Clinical Oncology conference, said on CNBC's "Power Lunch" that RBC Capital Markets was still defending the stock because it represents a long-term opportunity.
"The data looked as we expected," said Yee.
"We believe it's an overreaction and there is an event later this evening that we will follow up on and we think investors are probably going to come away from that feeling a little bit better after they present and go into some of the subgroup data later this evening"