"Burn me once, shame on you. Burn me twice, shame on me," seemed to be the message from InterMune's (Nasdaq: ITMN) investors yesterday.

Despite my assertion that the Committee for Medicinal Products for Human Use, or CHMP, recommendation was a guarantee that the European Commission would approve the drug, investors still sent the drugmaker up 8% yesterday. And it's up almost that much again today.

You'll recall that investors got burned by the Food and Drug Administration last year when an advisory panel recommended approving its lung drug Espriet, and then the FDA turned it down anyway. The decision shouldn't have come as a big surprise. It happened to Dendreon (Nasdaq: DNDN), Bristol-Myers Squibb (NYSE: BMY), and others before Espriet, and it's already happened since, with Orexigen's (Nasdaq: OREX) obesity drug Contrave being rejected last month after a positive panel recommendation.

The CHMP-EC relationship isn't like that. I only know of one drug, Johnson & Johnson's (NYSE: JNJ) antibiotic Zeftera, that didn't receive EC approval after a positive recommendation from CHMP, but that was because new data emerged during the final recommendation process. CHMP later changed its mind recommended against approving the drug.

Despite the routine nature of the EC rubber-stamp on CHMP recommendations, I guess that given the controversy surrounding Esbriet, a little fear of rejection was in order.

Investors might have also been reacting to InterMune's claims that it will be able to assert patent protection for Espriet well beyond the orphan drug exclusivity period, which ends in 2021. InterMune's patents aren't on the molecule itself, but on how it's used, and they won't expire until 2030. So-called "method of use" patents generally don't hold up well in the U.S., but management seemed confident on the conference call that Esbriet should be free from generic competition in the EU for quite a while.

At a market cap of $2.4 billion, InterMune has some, but certainly not all of the sales of Espriet priced in. The company thinks the market opportunity for Espriet in the top 10 EU countries is $3 billion. If it can hit half that number in a few years, it should be priced considerably higher than it is right now.

That is, if investors don't find something else to freak out about.

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