Dendreon (NASDAQ: DNDN) is a constant target for short-sellers, with shares down by a third for 2012 and the two-year graph looking even worse. But with a very important clinical trial on the way for Dendreon's Provenge in sequence with Johnson & Johnson's (JNJ -1.22%) drug Zytiga in a pre-chemo cancer indication, is the short-selling over? Motley Fool health care analyst David Williamson tells us why the shorts might be wrong on this one and why Dendreon might be due for a turnaround.