Prediction of extraprostatic extension by MRI tumor contact length: difference between anterior and posterior prostate cancer

Background: Tumor contact length (TCL) is defined as the extent of contact between prostate cancer and the prostatic capsule, and its predictive value for microscopic extraprostatic extension (EPE) has been reported. However, the impact of the zonal origin (anterior or posterior tumor) of the tumor on the diagnosis of EPE is controversial. Methods: We retrospectively analyzed the records of 233 consecutive patients who underwent preoperative MRI and radical prostatectomy. We designated their tumors as anterior or posterior, and evaluated the correlation between the TCL measured by MRI and microscopic EPE in the radical prostatectomy specimen. Then, we created the predicted probability curves for EPE versus TCL for anterior and posterior prostate cancer. Results: There were 109 patients (47%) with an anterior tumor and 124 patients (53%) with a posterior tumor. Postoperative pathological analysis confirmed pT3 in 18 patients (17%) with an anterior tumor and in 53 patients (43%) with a posterior tumor. Multivariate analysis demonstrated that the zonal origin of the tumor was an independent predictive factor for EPE. We developed separate probability curves of EPE versus TCL for anterior and posterior prostate cancer, which revealed that anterior tumors were less likely to invade the extraprostatic tissues. Among patients whose TCL was 10–20 mm, 9/32 patients (28%) with an anterior tumor had EPE compared with 24/45 patients (53%) with a posterior tumor (p = 0.036). The decision curve of this EPE predictive model had high clinical efficacy. Conclusions: Our results indicate that anterior tumors have more favorable pathological characteristics than posterior tumors with the same TCL measured by MRI. We constructed two separate predicted probability curves for EPE after discriminating anterior and posterior tumors, which will be useful for decision making in clinical practice.