Oh, Wall Street, how I love you for the wacky things you'll do from time to time. Take the case of Genentech (NYSE:DNA). While there are certainly valid reasons to be concerned about this leading biotech oncology franchise, the fact that sales of one product came in about $16 million shy of analyst guesstimates is not among them.

Genentech recorded another quarter of relatively heady growth. Product revenue rose another 42%, and all of the company's major ($100 million or more) drugs posted double-digit growth. Rituxan sales were up "only" 17%, while Avastin grew 72%, Herceptin more than doubled, Tarceva rose 47%, and Xolair rose 31%. Speaking of Avastin, you'll probably have read by now about how this important cancer drug "missed" the estimate -- posting a mere $423 million in sales, versus the median estimate of around $439 million.

To be fair, there are valid reasons to worry about Avastin. It's increasingly apparent that its off-label usage in lung cancer may have leveled off ahead of FDA approval later this year. And it isn't exactly great news that the FDA wants more data pertaining to a label extension application for breast cancer.

Genentech truly does have an impressive cancer franchise, but investors must accept that much of its near-term future growth will depend upon favorable follow-up studies of drugs like Herceptin and Avastin. Nor should you forget the meaningful options overhang, which could make some claims on future cash flows.

Considering that Genentech, Amgen (NASDAQ:AMGN), and Genzyme (NASDAQ:GENZ) have all endured tough sledding lately -- in contrast to Motley Fool Stock Advisor pick Biogen-Idec (NASDAQ:BIIB) -- investors' patience might be wearing a bit thin here. What's more, Genentech's neither cheap nor undiscovered. Still, if this slide continues, Foolish investors might begin to see the stock reach some interesting prices.

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Fool contributor Stephen Simpson has no financial interest in any stocks mentioned (that means he's neither long nor short the shares).