Pharmacyclics shares have tripled over the past year amid hopes that the company's lead asset, the BTK inhibitor ibrutinib, will prove an effective treatment for chronic lymphocytic leukemia (CLL) and other hematologic malignancies. The company's clinical data in CLL look good to me and I suspect the drug will receive FDA approval for late-stage patients, likely by the end of 2014. Yet Pharmacyclics already has a $3.5 billion market capitalization, will be entering competitive markets, and owns only 50% of ibrutinib's commercial rights following a partnership with Johnson & Johnson. Bulls are dreaming of a novel anti-cancer drug with efficacy across several cancer subtypes. Bears argue that the stock doesn't reflect the lower urgency of treating CLL -- the disease is not rapidly fatal, so ibrutinib's commercial ramp could be slow -- or the downside risk of clinical failure in other malignancies. Pharmacyclics feels too much like a valuation short for me to be interested. The bear case relies heavily on metrics -- disappointing non-CLL clinical data, which won't be available for at least two years, and commercial struggle in CLL -- that are too far away to be meaningful negative catalysts. I wouldn't buy the stock or be short right now. Sometimes, the best bet is not to play. Disclosure: Sadeghi has no positions in any of the stocks mentioned in this article. Follow Nathan Sadeghi-Nejad on Twitter.