William Blair analyst Andy Hsieh says he's an "aggressive" buyer of Exelixis with the stock down 28% since the Q4 earnings call on February 28. The previously announced Merck-Eisai collaboration agreement to jointly develop and commercialize Lenvima could serve as a comp to Exelixis's cabozantinib franchise, Hsieh tells investors in a research note. Eisai ascribes a value of roughly $7.9B for the Lenvima franchise, which equates to $26.66 per share for Exelixis, the analyst writes. With Exelixis trading at $6.3B in market cap or $5.8B in enterprise value, the current valuation does not account for the full potential of the cabozantinib franchise and does not include Cotellic, which is in three Phase III studies and being investigated in four oncology indications, Hsieh argues. He keeps an Outperform rating on the shares and believes the Merck-Eisai Deal highlights a "significant valuation disconnect."