This column was originally published on RealMoney on Oct. 11 at 3:08 p.m. EDT. It's being republished as a bonus for TheStreet.com readers.Since early 2003, Genentech's ( DNA) stock has been on a phenomenal tear. It's up fourfold, which is amazing when you consider that it sported a $20 billion market capitalization at its outset. In these last two-and-a-half years, management's sharp focus on extremely well-validated science and large, unmet markets has borne tremendous fruit for shareholders. The company has long been a key holding for the biotech intelligentsia as a result of management's scientific slant, but the company's clinical success has been nothing short of astounding: It has been batting nearly 1.000 since 2003 in drug trials. Shareholders who have been patient enough to hold tight have been rewarded over and over, and the stock became a self-fulfilling prophesy of success, almost hitting $100 per share before a few concerns emerged that sent the stock into the $80s. While Genentech's financial future undoubtedly looks bright, Genentech's stock still carries an incredibly high valuation by any metric. Investors must ask, "What am I paying for and what should I expect in return as a Genentech shareholder?" I believe that most prudent long-term investors will conclude that they're paying for a great company, but one that's so fully valued it won't deliver the kind of returns that will make its considerable risks worthwhile.