Researchers Propose A New Validated Prostate Cancer Staging System

A new study detailed the development and validation of a clinical prognostic stage group system for nonmetastatic prostate cancer.

“In 2016, the American Joint Committee on Cancer (AJCC) established criteria to evaluate prediction models for staging. No localized prostate cancer models were endorsed by the Precision Medicine Core committee, and 8th edition staging was based on expert consensus,” the researchers explained.

“Localized prostate cancer is sometimes less aggressive, sometimes more—and whether we’re patients, physicians or researchers, we all want to know as best we can how aggressive a particular cancer is likely to be,” says study co-first author Robert Dess, MD, an assistant professor of radiation oncology at Michigan Medicine, in a press release. “That information helps with our conversations with patients, it helps with clinical trial design and it is particularly valuable when you can make those estimates based off of standard information that you would collect when you first see a patient to discuss their treatment options.”

“None of the previous models evaluated met the criteria, so none of them could be used,” said study co-senior author Daniel Spratt, MD, the Laurie Snow Endowed Research Professor of Radiation Oncology at Michigan Medicine. “So we said, ‘Well, let’s make one.’ We wanted it to be transparent, robust and validated, so that we can start moving closer to communicate using a common staging system, similar to other cancers. Right now we primarily categorize people as low risk, intermediate risk or high risk — which is a fairly blunt and imprecise system.”

To develop a validate a new staging system, Drs. Dess and Spratt and their colleagues identified patients with cT1-4N0-1M0 prostate adenocarcinoma between Jan. 1, 1992, and Dec. 31, 2013, with follow-up completed Dec. 31, 2017. Patients were identified from seven centers from the United States, Canada, and Europe; the Shared Equal Access Regional Cancer Hospital (SEARCH) Veterans Affairs Medical Centers collaborative (five centers); and the Cancer of the Prostate Strategic Urologic Research Endeavor (CaPSURE) registry (43 centers) (the STAR-CAP cohort). Patients from the STAR-CAP cohort were randomized into training and validation datasets. A second validation set was obtained from the Surveillance, Epidemiology, and End Results (SEER) Program. The exposures were curative intent radial prostatectomy (RP) or radiotherapy with or without androgen deprivation therapy. The main outcome measure was prostate cancer-specific mortality.

The researchers developed a points-based Score staging system based on a competing-risk regression model; they analyzed model discrimination (C index), calibration, and overall performance in the validation cohorts.

A total of 19,684 patients with a median (interquartile range [IRQ]) age of 64 (59-70) years were included in the study. Median (IQR) follow-up was 71.8 (34.3-124.3) months, with at least 20.7% of the patients followed for at least 10 years. Most patients were treated with RP (n=12,421); 7,263 underwent radiotherapy.

The predicted 10-year prostate cancer-specific mortality in the validation set across the nine Score groups ranged from 0.3% to 40.0%.

“The 10-year C index (0.796; 95% CI, 0.760-0.828) exceeded that of the AJCC 8th edition (0.757; 95% CI, 0.719-0.792), which was improved across age, race, and treatment modality and within the SEER validation cohort,” the authors further observed. Their Score system outperformed the National Comprehensive Cancer Network and Cancer of the Prostate Risk Assessment risk grouping 3- and 4-tier classification systems.

The results of the study were published in JAMA Oncology.