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 Bristol-Myers Squibb Co. (NYSE:BMY) rallied more than 2% today after BMO Capital Markets upgraded the pharmaceutical giant from market perform to outperform.

So what: Along with the upgrade, analyst Alex Arfaei boosted his price target to $60 (from $56), representing about 19% worth of upside to Friday's close. While momentum traders might be turned off by the stock's steady slide over the past month, Arfaei thinks that it's a good time to jump in given Bristol-Myers' still-appealing growth prospects and seemingly inexpensive valuation.

Now what: According to BMO, Bristol-Myers' risk/reward trade-off is pretty attractive at this point. "We are upgrading BMY to Outperform from Market Perform based on our more positive outlook for the company's immuno-oncology (IO) pipeline and lower market expectations following the recent update on the Checkmate-012 trial... Now $60/share using DCF," noted Arfaei. "Investors should buy BMY prior to ASCO and should not interpret potentially positive updates for MK-3475 as negative for BMY; this market will likely be large enough to accommodate multiple players." With Bristol-Myers still up more than 40% from its 52-week lows and trading at a 30-plus forward P/E, however, I'd wait for an even wider margin of safety before buying into that bullishness.