For better or worse, treatment for prostate cancer is more common than it otherwise would be in the absence of widespread PSA testing. Those treatments are, of course, designed to address cancer present in the prostate (few of which would actually kill the patient), but they do other things as well, including increasing the risk of incontinence and impotence.
Two specific studies on quality of life after prostate-cancer treatment have been performed for men participating in Rotterdam and Sweden. Preoperatively, 1 to 2% of the men were incontinent and 31 to 40% were impotent. At 18 to 52 months after treatment, incontinence was reported in 6 to 16% of the men undergoing radical prostatectomy and in 3% of those undergoing radiation therapy. At 6 to 52 months after treatment, impotence among men who were potent preoperatively was reported in 83 to 88% of those undergoing radical prostatectomy and in 42 to 66% of those undergoing radiation therapy.
The study authors designed a simulation that incorporates these effects to estimate in quality-adjusted life years (QALYs) associated with PSA testing. Harold Sox, in the accompanying editorial, explains the simulation as follows:
The authors used a form of modeling that simulates a patient’s passage through a sequence of health states to death. Each state is characterized by the annual probability of transitioning to other states and by a quality weight (called a utility), which reflects patients’ feelings about being in that state. The model calculates the years spent in each health state weighted by the utility of that state. The sum of these quality-adjusted years over the health states experienced in the patient’s pathway to death is the quality-adjusted length of life. By repeating this process many times, the model simulates the experience of a population of patients.
The study found:
Per 1000 men of all ages who were followed for their entire life span, we predicted that annual screening of men between the ages of 55 and 69 years would result in nine fewer deaths from prostate cancer (28% reduction), 14 fewer men receiving palliative therapy (35% reduction), and a total of 73 life-years gained (average, 8.4 years per prostate-cancer death avoided). The number of QALYs that were gained was 56 (range, −21 to 97), a reduction of 23% from unadjusted life-years gained. To prevent one prostate-cancer death, 98 men would need to be screened and 5 cancers would need to be detected. Screening of all men between the ages of 55 and 74 would result in more life-years gained (82) but the same number of QALYs (56). […]
[B]ecause of a long lead time until clinical symptoms would develop from screen-detected tumors (estimated at 5 to 12 years), men would have an increased number of years of living with these adverse effects [incontinence, impotence]. […]
A substantial part of the predicted difference between life-years and QALYs gained is caused by overdiagnosed cancers.
The editorial offers some caution:
What does this result tell us? It says that the net effect of prostate-cancer screening can be a loss or a gain, depending on patients’ utilities for their potential future health states. It is tempting to speculate that most patients will gain, since the range of net benefit is larger for gains (0 to 97.1 life-years) than for losses (0 to −20.7 years). These data do not support that conclusion, because we do not know the number of patients with low utilities for the health states, as compared with the number with higher utilities. If we knew that all patients have utilities consistent with a gain in quality-adjusted life-years, we could recommend universal screening.
But, we don’t know that all patients have utilities consistent with a gain in QALYs. Sox recommends a shared decision making approach, which is not what the USPSTF suggested.