This year was supposed to be one of meteoric growth for Dendreon. Seattle’s largest biotech company already had rocketed in less than two years from 180 employees to about 2,000. It was in the midst of rolling out its prostate-cancer treatment, Provenge, after years of gains, setbacks and delays. JPMorgan’s biotech team proclaimed the stock “our top pick for 2011.” Then Wednesday, it fell swiftly out of favor. Dendreon slashed its 2011 sales forecast, said layoffs are coming and posted second-quarter gross revenue of $51 million, about $7 million short of analysts’ expectations.