Exelixis (Nasdaq: EXEL) plunged 40% last week after the company informed investors it’ll go ahead with its intention to run pivotal Phase III trials of cabozantinib (cabo) for castration-resistant prostate cancer (CRPC) despite not getting an agreement on a Special Protocol Assesment with the FDA. Exelixis announced very positive results from a Phase III clinical trial of cabo in medullary thyroid cancer the week before. Although it’s a small indication from a commercial standpoint, it provides a clinical validation of Exelixis’ main drug and sets it for a potential approval in 2012. Exelixis plans to initiate a rolling NDA submission for this indication this quarter. The filing will be completed in 1H 2012.