While Fools should generally take the opinion of Wall Street with a grain of salt, it's not a bad idea to take a look at particularly stock-shaking analyst upgrades and downgrades -- just in case their reasoning behind the call makes sense.

What: Shares of InterMune, Inc. (UNKNOWN:ITMN.DL) popped about 4% in premarket trading Tuesday after Goldman Sachs upgraded the biotechnology company from neutral to buy.

So what: Along with the upgrade, analyst Terence Flynn boosted his price target to $45 (from $40), representing about 34% worth of upside to yesterday's close. So while contrarians might be turned off by the stock's massive year-to-date surge, Flynn's call suggests that InterMune's growth potential gives it plenty of room to run.

Now what: Goldman raised its 2015 per-share view for InterMune from ($0.32) to ($0.04) and its 2016 outlook from $1.02 to $1.56. "In late February, ITMN reported better-than- expected top-line Ph3 data for key drug, Esbriet for IPF (an orphan lung indication), which in our view de-risks the US opportunity (we model $1.3bn US peak)," said Flynn. "Our conversations with investors suggest outstanding concerns regarding Esbriet's efficacy (treatment effect size) as well as the competitive landscape." Of course, with the stock already up a whopping 135% in 2014, I'd wait for a much wider margin of safety before jumping in.