The SEC is investigating whether officials at the Center for Medicare and Medicaid Services (CMS) tipped off a policy research group about the agency's review of Dendreon's ($DNDN) cancer vaccine, Provenge, The Wall Street Journal reports. Dendreon's stock plunged 26% between June 1, 2010, and the close of trading on June 30, just before CMS announced a decision to consider setting coverage limits on the treatment. More (sub. req.)