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

What: Shares of Clovis Oncology Inc (NASDAQ:CLVS) surged 7% today after Stifel upgraded the biopharmaceutical company from hold to buy.

So what: Along with the upgrade, analyst Brian Klein planted a price target of $50 on the stock, representing 30% worth of upside to yesterday's close. So while momentum traders might be turned off by Clovis' sharp price decline in recent months, Klein's call could reflect a sense on Wall Street that its pipeline prospects are just too cheap to pass up.

Now what: According to Stifel, Clovis' risk/reward trade-off is rather attractive at this point. "Following the significant pull-back of ~60% from recent highs, we believe Clovis now presents with significant upside potential based on clinical and commercial prospects for CO-1686 in second-line EGFR-mutant NSCLC with T790M mutation," said Klein. "While we still remain conservative on approval timing and potential in earlier-stage disease, and note safety/tolerability concerns (particularly hyperglycemia), we view '1686 as a compelling and commercially viable, clinical candidate." So while Clovis remains just too speculative for average Fools, biotech-savvy contrarians might want to follow Stifel's lead.