Errors in histological grading by prostatic needle biopsy specimens: frequency and predisposing factors

Sampling error is an inherent problem of prostate biopsy. Consequently, the re are problems in determining whether a given carcinoma is clinically sign ificant on the basis of biopsy results. This study assesses the factors tha t predispose to errors in biopsy grading, as well, as the dimensions of sam pling error due to these factors. Among 187 cases, biopsy grading error was retrospectively related to grade heterogeneity in the prostate and to biop sy-related factors. Clinically relevant biopsy grading errors occurred in a quarter of the cases. Of all grading errors, at least 17% resulted from mi sinterpretation by the pathologist only. Overall, prostates with grade hete rogeneity revealed grading errors twice as frequently as specimens without grade heterogeneity. In most cases, however, grading error resulted from mu ltiple factors, such as the number and length of cores obtained (p < 0.05). This was an important finding because the mean core length was only 9.4 mm , whereas the biopsy needle is designed to obtain cores of 35 mm. Moreover, clinically relevant biopsy grading error had occurred in almost half of th e cases when the Gleason score was based on a tumour deposit measuring less than 0.5 mm (p < 0.05). The clinical consequences of these findings are im portant. Clinicians should try to obtain at least six biopsies, each 15 mm in length, to minimize grading error. Pathologists should be cautious in re porting Gleason scores based on tumour lesions smaller than 400x total magn ification field. Interpretation could be refined, when necessary, by warnin g the urologist of the Limitations of the biopsy report. Copyright (C) 2000 John Wiley & Sons, Ltd.