You could certainly say that Janet Yellen met or bested expectations in her first testimony to Congress as Federal Reserve chairwoman today, as evidenced by the broad-based rally in the S&P 500 (^GSPC -1.26%).

As my Foolish colleague Travis Hoium noted earlier, there were some important takeaways from Yellen's testimony since the majority of other market-moving news was earnings related -- the major economic data doesn't pick up until tomorrow.

Yellen's testimony pointed toward continued gradual easing of the Fed's economic stimulus, echoing comments from her predecessor, Ben Bernanke. Gradual easing, as opposed to a sudden removal of this stimulus, should lead to a reasonably slow rise in long-term lending rates. This would obviously be viewed as good news for consumers, as well as banks and the housing industry which are counting on low lending rates to drive loan origination and refinancing activity.

In addition, Yellen noted that the Fed's original target for raising lending rates when the U.S. unemployment rate hit 6.5% was more of a soft target and open to interpretation. Some investors on Wall Street had grown worried given that the unemployment rate fell to 6.6% in January, but jobs creation, overall, has been pretty weak the past two months. If not for a falling labor participation rate, it's quite possible that unemployment would still be at 7% or greater.

By day's end, the "Yellen effect" had pushed the S&P 500 decisively higher by 19.91 points (1.11%) to close at 1,819.75, the index's fourth straight day of gains.

Leading all S&P stocks to the upside was biopharmaceutical company Cadence Pharmaceuticals (NASDAQ: CADX), which gained 26.5% after agreeing to be purchased for $1.3 billion, or $14 per share in cash, by Mallinckrodt (MNK). According to the press release from Mallinckrodt, the acquisition will be mildly accretive to its 2014 earnings per share and "significantly accretive" to its fiscal 2015 EPS. The acquisition aids Mallinckrodt by bringing FDA-approved intravenous acetaminophen injection Ofirmev into its product portfolio while also allowing the company to rely on Cadence's adjacent hospital market partnerships to possibly expand into new ventures. Cadence Pharmaceuticals shareholders, meanwhile, get a hefty premium to yesterday's closing price, which seems more than fair.

Shares of Relypsa (RLYP), a clinical-stage biopharmaceutical company developing nonabsorbed polymeric drugs to treat renal, cardiovascular, and metabolic diseases, popped 18.9% after research firm Stifel Nicolaus maintained its buy rating on the company and bumped its price target to $41 from $25. This is the second time since December that Stifel Nicolaus has boosted its price target on Relypsa. As Stifel noted then, the company's lead hyperkalemia drug, patiromer, has demonstrated solid results in clinical studies and could become a long-term solution for chronic kidney disease sufferers faced with currently inadequate therapies. While I wouldn't deny that Relypsa's study results have been intriguing thus far, with the stock nearly quadrupling since its IPO I'd contend that much of that optimism has already been baked into its share price.

Finally, medical robotics company Hansen Medical (HNSN), which develops devices for positioning, manipulating, and controlling catheters, advanced 12.6% after reporting clearance from the Food and Drug Administration for its Magellan 6Fr Robotic Catheter. This new device is an improvement over the existing Magellan 9Fr Robotic Catheter in that it possesses novel dual-bend technology and features a smaller outer diameter catheter for use in smaller vessels in the peripheral vasculature. While new approvals are always a good thing, and innovation is what drives medical device companies forward, I still don't see a reasonably quick pathway to profit for Hansen Medical. This means with Hansen's cash burn continuing that a dilutive share offering remains a possibility.