Nomogram predicts overdiagnosis in prostate cancer screening

US researchers have developed a nomogram which they say can be used to predict whether prostate cancer has been overdiagnosed in individual patients diagnosed following prostate-specific antigen (PSA) screening.

It is based on a model designed to distinguish men who, in the absence of screening, would have died from other causes before the diagnosis of prostate cancer, and therefore spared them undergoing treatment for the disease, with its subsequent side effects and emotional consequences.

The research team, led by Roman Gulati (Fred Hutchinson Cancer Research Center, Seattle, Washington, USA), developed a microsimulation model of prostate cancer natural history in the presence or absence of screening, using data from prostate cancer screening trials, national mortality data, and cancer registry data.

They then used the model to produce virtual life histories for 10,000 hypothetical men diagnosed with nonmetastatic prostate cancer through PSA testing in the year 2005, and fitted these data to a logistic regression model to predict overdiagnosis based on age, Gleason score, and PSA level at diagnosis.

The team found that age was the single most important factor determining the risk for overdiagnosis, with each additional year conferring a 12.9% increased odds. Meanwhile, a Gleason score of 7 or more was associated with a 19.5% decrease in the odds for overdiagnosis versus lower scores, and each additional 1 ng/mL serum PSA up to 10 ng/mL was associated with a 16.6% decrease in the odds for overdiagnosis.

They found that the predictions were reasonably accurate with an area under the receiver operating characteristic curve of 0.75.

Writing in the Journal of the National Cancer Institute, Gulati et al say that “the results of this study extend our understanding of the range of risks of overdiagnosis… and how they depend on patient and tumor characteristics.”

They add: “It is hoped that the resulting nomogram, tailored to individual patient characteristics known at diagnosis, will provide useful information for patients and their physicians seeking to weigh the likely harms and benefits of the treatment options available for contemporary screen-detected prostate cancers.”

However, in an accompanying editorial, Boris Freidlin and Edward Korn, from the National Cancer Institute in Bethesda, Maryland, USA, call into question the utility of the nomogram. They argue that, although microsimulation data are useful for guiding public health strategy around the implementation of screening programs, once a patient has actually received a diagnosis of prostate cancer, they become much less relevant.

“[F]or the purpose of guiding patient treatment decisions, the most useful and directly relevant information is, for each possible treatment, its morbidity and the probability of having symptoms from, or dying from, prostate cancer at various times in the future given the patient’s prognostic information.”

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