SEATTLE ( TheStreet) -- The ability of Dendreon's ( DNDN) Provenge to prolong the survival of prostate cancer patients without having any measurable effect on the tumor is called "surprising" and "hard to understand" in an editorial published Wednesday night in the New England Journal of Medicine. None of the criticisms leveled at Provenge in the editorial authored by Dr. Dan Long, a deputy editor at the New England Journal of Medicine (NEJM), are particularly new or surprising. But the imprimatur of the NEJM, the most prestigious medical journal in the country, does carry weight with doctors and patients. Dendreon shares closed Wednesday down 4% to $33.39 in advance of the NEJM lifting its embargo on the Provenge editorial at 5 pm EDT. The stock fell 8% in the past two days. Some subscribers to the print edition of the NEJM received their issues on Tuesday and it's known that copies of the Provenge editorial were shared amongst Wall Street's healthcare trading desks prior to the lifting of the media embargo. The U.S. Food and Drug Administration approved Dendreon's Provenge in April as a treatment for prostate cancer based on a pivotal study known as "IMPACT" which demonstrated treatment with the cancer immunotherapy prolonged survival by 4.1 months compared to treatment with a placebo. Even with the uncertainty over Provenge's approval settled, Dendreon's stock continues to be volatile as investors watch the commercial launch of Provenge with keen interest. Wall Street's focus on Dendreon ramped even more after the federal agency that oversees Medicare said it was evaluating Provenge to determine a national coverage decision. Data from the pivotal Provenge IMPACT study is also published in this week's NEJM, but is not different than results presented previously at medical meetings and by Dendreon. The survival advantage in prostate cancer demonstrated by Provenge comes with no evidence that the therapy shrinks tumors or even delays tumor growth. This somewhat counter-intuitive outcome of the Provenge clinical trials is long known and didn't bother FDA enough to get in the way of the drug's approval. Longo, however, raises the issue again in his NEJM editorial: "The prolongation of survival without a measurable antitumor effect is surprising," Long writes. "It is hard to understand how the natural history of a cancer can be affected without some apparent measurable change in the tumor, either evidence of tumor shrinkage or at least disease stabilization reflected in a delay in tumor progression. This lack of tumor effect raises concerns that the results could have been influenced by an unmeasured prognostic variable that was accidentally imbalanced in study-group assignments."