Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of pharmaceutical company Spectrum Pharmaceuticals (NASDAQ:SPPI) plummeted 36% today after issuing a full-year revenue outlook that disappointed Wall Street.

So what: Spectrum that said that 2013 sales of its chemotherapy side-effect drug Fusilev will be in the range of only $80 million-$90 million (representing a whopping 56% decline from 2012), forcing analysts to drastically recalibrate their valuation estimates. While demand from doctors remains stable, management admitted that hospitals are certainly shifting to generics, reinforcing serious concerns over Fusilev's peak sales potential.

Now what: Management now sees 2013 total revenue of $160 million-$180 million, down about a third from 2012 and well below Wall Street's view of $297 million.

"The Company believes the majority of the impact from the change in ordering patterns will be reflected in the first half of 2013 and expects to return to a run-rate that more closely aligns with end-user demand by the end of the year," Spectrum reassured investors in a statement.

So while the stock remains a bit too speculative for conservative Fools, today's pullback might be a tasty opportunity for less risk-averse, short-term-oriented contrarians.