Goldman Sachs analyst Paul Choi started Puma Biotechnology with a Sell rating and $42 price target. The analyst sees see 11% downside in the shares versus 20% upside on average for his coverage universe. While the company's Nerlynx launch in the extended adjuvant setting in HER2+ breast cancer has gone well to date, channel checks and analysis suggest that consensus estimates are overly optimistic with respect to patient adds in this setting, Choi tells investors in a research note. The analyst initiated coverage of the smid-cap biotech sector with a Neutral coverage view. He views sector fundamentals as healthy but says high valuations temper his enthusiasm.