Study Seeks to Determine Whether Ovarian Cancer Screenings Are Worth It
According to received wisdom, prevention is better than cure: but received wisdom, even when not altogether wrong, sometimes requires refinement. What might be true of individuals is not necessarily true of whole populations, and vice versa. Even after years of intense study, the correct but unsatisfying answer to the question of whether prevention is better than cure may well be, "It depends."
The prognosis of ovarian cancer is relatively poor, with a 5-year survival rate of about 40 percent. It stands to reason that early detection might improve survival because of earlier detection and treatment; but what stands to reason is not always a good guide to reality.
A trial organized in Britain and reported in a recent edition of the Lancet tried to answer the question of whether annual screening of women between the ages of 50 and 70 by one of two different methods (blood test and ultrasound) would result in a reduced death rate from ovarian cancer. If nothing else it was a triumph of organization.
The investigators estimated that they needed a trial of 200,000 women to demonstrate a difference between experimental groups and controls. They contacted 1,243,202 women they thought might be eligible to take part in the trial, of whom 172,149 refused to participate and 776,626 did not respond. After exclusions, the investigators were able to find slightly more than the 200,000 they thought they needed. 50,640 were assigned at random to annual screening by blood test, 50,639 to ultrasound screening, and 101,359 to no screening at all. They followed them up for up to 14 years, remarkably few being lost in the process, only 1313 of the original 202,546.
The results of this giant effort were equivocal, as they so often are. In total, 649 women died during the trial of ovarian cancer, 347 in the unscreened population and 302 in the screened population. The reduction in death rate among the screened group was about 15 percent, which failed to reach statistical significance. However, mortality in the screened groups after seven years began to diverge from that in the unscreened, and the authors concluded that, if they had waited longer, a greater and statistically significant divergence might have emerged.