NEW YORK ( TheStreet) -- Seattle Genetics ( SGEN) shares have risen nearly 28% since I first wrote about the company in March, even as tepid third-quarter sales of the cancer drug Adcetris -- down sequentially despite a 3.5% midsummer price hike -- forced management to cut guidance for the rest of the year. Last week, my colleague Adam Feuerstein tweeted a brutally apt synopsis of Seattle Genetics: "Seems like bears have been right about Adcetris market being small, wrong on the stock." Ouch. The truth hurts. Seattle Genetics at $23.11 and a $2.74 billion market cap is almost comically overvalued -- more than 20 times this year's revised Adcetris sales guidance. Management even concedes Adcetris sales will be essentially flat in 2013. Despite the lofty valuation, Seattle Genetic bulls have thus far clung with astonishing patience to the hope for eventual Adcetris sales growth following expansion of the drug's label. The problem is FDA label expansion, which would initially include retreatment and long-term use data, won't happen until late 2013 at the earliest. Frankly, I'm not convinced there's a compelling investment case to be made either way at this point. Adcetris is an anti-CD30 monoclonal antibody linked to the tumor-killing drug monomethyl auristatin E (MMAE). The "antibody-drug conjugate" received FDA approval in August 2011 for relapsed/refractory Hodgkin's lymphoma (HL) and systemic anaplastic large cell lymphoma (sALCL). Adcetris is an effective treatment option for these patients, but the company's third-quarter results confirmed my view that Wall Street estimates were too high and that the drug's current "on label" market is miniscule. Predictably, most sellside analysts either downgraded or lowered sales forecasts in frustration after last week's conference call. Seattle Genetics' shares have declined sharply from early September highs, but with Adcetris sales expectations now lowered, further evidence of commercial stagnation isn't likely to be a catalyst for additional downside. Let's take a closer look at the company's label expansion opportunities. Seattle Genetics is conducting phase III trials of Adcetris in relapsed cutaneous T-cell lymphoma (CTCL), front-line HL, and will soon start a study in front-line mature T-cell lymphoma (MTCL). Even though Adcetris may prove effective in these studies, data are a long way off. Results from the phase III trial in CTCL won't be available until late 2014 or 2015, and readouts from the other two studies won't likely occur until at least 2017. These new cancer indications are larger than those Adcetris is currently approved for but not enough to get excited about buying the stock now, particularly since the study results are so far off. The company should receive FDA approval late next year for an expanded label that will include data for retreatment and long-term use of Adcetris in HL and sALCL. Bulls hope this expanded label will re-ignite sales growth in the drug's initial indications. I'm not convinced physicians will dramatically alter treatment patterns based on the company's data.