Screening for ovarian cancer doesn't reduce mortality

Simultaneous screening with serum cancer antigen (CA)-125 and transvaginal ultrasound does not reduce the number of deaths from ovarian cancer, according to the findings from the large, randomized Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial.

From 1993 to 2001, researchers from leading medical institutions across the United States assigned more than 78,000 women between the ages of 55 and 74 years to either annual screening with CA-125 for 6 years and transvaginal ultrasound for 4 years or usual medical care. The researchers followed the women for a maximum of 13 years.

They diagnosed ovarian cancer in 212 women in the intervention group and in 176 women in the usual care group (rate ratio [RR], 1.21; 95% CI, 0.99-1.48). Similarly, they noted 118 deaths from ovarian cancer in the intervention group and 100 deaths in the usual care group (mortality RR, 1.18; 95% CI, 0.82-1.71). Deaths due to other causes (excluding ovarian, colorectal, and lung cancers) totaled 2,924 in the intervention group and 2,914 in the usual care group (RR, 1.01; 95% CI, 0.96-1.06). Participant characteristics between the 2 study groups were virtually identical at baseline and follow-up, as were stage-specific treatments. Compliance with screening was high in the intervention group, and contamination was low in the usual care group.

The absence of a stage-shift in the study (ie, a decrease in the absolute number of late stage [III or IV] cases in the intervention group compared with the usual care group) suggests the cutoffs used in the trial for screening positivity were not effective at detecting ovarian cancer in a nonadvanced stage. Studies suggest that ovarian tumors must be found when they are smaller than the current threshold used for transvaginal ultrasound (10 cm³ for cysts) and that the currently used CA-125 threshold should be lower than 35 units per milliliter. However, lowering the thresholds would increase the number of false-positive results.

Other trials are ongoing to determine how best to reduce mortality from ovarian cancer through screening. Until then, the current approach, according to the authors of this study, seems to do little more than "increase invasive medical procedures and associated harms."

Buys SS, Partridge E, Black A, et al. Effect of screening on ovarian cancer mortality: The Prostate, Lung, Colorectal and Ovarian (PLCO) Cancer Screening Randomized Controlled Trial. JAMA. 2011;305(22):2295-2303.