Clinicopathologic analysis of extracapsular extension in prostate cancer: Should the clinical target volume be expanded posterolaterally to account for microscopic extension?

Purpose: We performed a complete pathologic analysis examining extracapsular extension (ECE) and microscopic spread of malignant cells beyond the prostate capsule to determine whether and when clinical target volume (CTV) expansion should be performed. Methods and Materials: A detailed pathologic analysis was performed for 371 prostatectomy specimens. All slides from each case were reviewed by a single pathologist (N.S.G.). The ECE status and ECE distance, defined as the maximal linear radial distance of malignant cells beyond the capsule, were recorded. Results: A total of 121 patients (33%) were found to have ECE (68 unilateral, 53 bilateral). Median ECE distance = 2.4 mm [range: 0.05–7.0 mm]. The 90th-percentile distance = 5.0 mm. Of the 121 cases with ECE, 55% had ECE distance ≥2 mm, 19% ≥4 mm, and 6% ≥6 mm. ECE occurred primarily posterolaterally along the neurovascular bundle in all cases. Pretreatment prostrate-specific antigen (PSA), biopsy Gleason, pathologic Gleason, clinical stage, bilateral involvement, positive margins, percentage of gland involved, and maximal tumor dimension were associated with presence of ECE. Both PSA and Gleason score were associated with ECE distance. In all 371 patients, for those with either pretreatment PSA ≥10 or biopsy Gleason score ≥7, 21% had ECE ≥2 mm and 5% ≥4 mm beyond the capsule. For patients with both of these risk factors, 49% had ECE ≥2 mm and 21% ≥4 mm. Conclusions: For prostate cancer with ECE, the median linear distance of ECE was 2.4 mm and occurred primarily posterolaterally. Although only 5% of patients demonstrate ECE >4 to 5 mm beyond the capsule, this risk may exceed 20% in patients with PSA ≥10 ng/ml and biopsy Gleason score ≥7. As imaging techniques improve for prostate capsule delineation and as radiotherapy delivery techniques increase in accuracy, a posterolateral CTV expansion should be considered for patients at high risk.