Prostate cancer collaborative stage data items--their definitions, quality, usage, and clinical implications: a review of SEER data for 2004-2010.

Background: Version 2 of the Collaborative Stage Data Collection System (CSv2) became effective with cases diagnosed in 2010. This report focuses on the CSv2 components required to derive the American Joint Committee on Cancer (AJCC) stage for prostate cancer and on the site-specific factors for prostate cancer captured in CSv2. The report also highlights differences between the AJCC 6th and 7th editions for classifying prostate cancer stage.

Methods: Data from 18 Surveillance, Epidemiology, and End Results (SEER) Program population-based registries (SEER-18) were analyzed for the years 2004-2010, which included 400,591 prostate cancer cases.

Results: CSv2 provides specificity with regard to the Gleason grading system by distinguishing between clinical and pathologic patterns and scores. The AJCC 7th edition incorporates prostate-specific antigen values into staging, subdivides stage II into IIA and IIB, and reclassifies extraprostatic invasion with microscopic bladder neck invasion from T4 in the 6th edition to T3a; this latter change affected the AJCC stage of 283 cases in 2010. Of the 44,578 prostate cancer cases diagnosed in 2010 that would have been classified as stage II in the AJCC 6th edition, 32.7%, 27.5%, and 39.8% are classified as stages I, IIA, and IIB, respectively, in the 7th edition.

Conclusions: CSv2 provides more information than was previously available to researchers using SEER prostate data. The absence of a clearly defined clinical stage for each prostate case is the overriding limitation that researchers face in relying on Collaborative Stage information to analyze prostate cancer data.