Shares of Puma Biotechnology, Inc. (PBYI) have plunged 38.4% in the past three months compared with the industry’s decline of 4.8%.The company’s sole marketed product, Nerlynx (neratinib), is approved for the treatment of early-stage HER2-positive breast cancer in patients who have been previously treated with Roche’s (RHHBY) Herceptin-based adjuvant therapy.Demand for Nerlynx has been declining in recent quarters. Owing to this, sales of the drug have been falling over the past couple of quarters. Being th ...