Discontinuous foci of cancer in a single core of prostatic biopsy: when it occurs and performance of quantification methods in a private-practice setting.

In addition to clinical data, prostatic biopsy (Bx) reports orient urologists in outlining the patient's treatment options. Discontinuous involvement of a core by multiple foci of cancer is not infrequent; however, there is currently no consensus as to which method of quantification should be the standard. We applied 2 distinct approaches to quantify the length of cancer foci in the Bx and compared the results to prostatectomy (RP) parameters. All patients with matched Bx and RP treated by the same medical team between 2006 and 2010 were consecutively included in the study. Tumor extent in the Bx was estimated by multiple approaches, and the length was measured in millimeters. The subset of cases with discontinuous foci of cancer in a single core was initially reported by adding each foci and ignoring the benign intervening prostatic tissue, which was designated as additive quantification (AQ). Upon slide review, these foci were reassessed as a single focus and measured by linear quantification (LQ). RPs were partially embedded according to the International Society of Urological Pathology recommendations, and the percentage of tumor was evaluated with graphic precision. Mean percentage of the tumor in RP (%RP) and in the Bx were arbitrarily classified as limited (<6%) and nonlimited (≥6%). Bx parameters were then correlated with %RP and margin status. All methods of quantification of the tumor in the Bx obtained excellent correlation with %RP. LQ and AQ diverged in 14/38 patients, with a mean total length of cancer of 5.8 mm more than the length obtained by LQ in the same population, accurately upgrading 6/14 cases to nonlimited. This subset (LQ>AQ) was more often seen in Bx with significantly more positive cores (P=0.003) of predominantly Gleason score 7 and associated with positive surgical margins in RP (P=0.034) independent of %RP (21% vs. 19% in the margin-negative cases). However, in the subset of Bx in which the tumor infiltration was continuous (AQ=AL) positive margins were indeed associated with tumor extent (31% vs. 6% in margin-negative cases). Discontinuous foci of cancer in a single core were most often seen in Bx sampling nonlimited disease, and this event was associated with positive surgical margins. LQ of cancer improved the performance of the Bx in predicting RP tumor extent relative to the traditional millimetric sum. Our findings support the idea that discontinuous foci may represent undersampling of a larger irregular nodule; however, this study is based on routine reports and does not directly access tumor biology.