Purpose: We determine whether a new parameter, the amount of tumor in contact with the fibromuscular rim (capsule) of the prostate, correlates with extraprostatic extension, and ascertain whether estimating the new parameter using transrectal ultrasonography can predict extraprostatic extension.
Materials and methods: We analyzed step sectioned prostatectomy specimens from 189 patients who had had positive peripheral zone biopsies. We measured the contact length, maximum length (mm.) of the portion of the peripheral zone cancer that was in contact with the fibromuscular rim, and determined the contact ratio from the quotient (%) of the contact length divided by the tumor circumference. We evaluated the correlation between the pathological and ultrasound measurements of these parameters, as well as the accuracy of these criteria for predicting microscopic extraprostatic extension.
Results: Among the 189 cancers there was a significant difference (p <0.0001) between organ confined tumors and tumors with extraprostatic extension in contact length and contact ratio. There was a positive correlation (r = 0.691) between the contact lengths measured ultrasonically and histologically among 95 patients who had hypoechoic lesions associated with positive biopsies. A receiver operating characteristics curve of the ability of ultrasound estimated contact length to predict extraprostatic extension revealed the best cutoff value to be 23 mm. with 77% accuracy. Logistic regression analysis revealed that pathological contact length correlated better with extraprostatic extension than tumor volume, Gleason score, prostate specific antigen (PSA) level and pathological contact ratio. The best preoperative predictor of extraprostatic extension was the ultrasound contact length, followed by the contact ratio, PSA value, percentage of the biopsy specimen that was cancer and presence of perineural invasion in the biopsy specimen. Multiple logistic regression analysis revealed that the predictability of ultrasound contact length was improved by considering PSA value also. Probability plots for predicting extraprostatic extension were developed by combination of ultrasound contact length with PSA value.
Conclusions: The length of tumor contact with the fibromuscular rim is more significantly related to extraprostatic extension than tumor volume, PSA level and tumor grade. For hypoechoic cancers a new ultrasound staging criterion, contact length, has been defined. For men who are clinically candidates for radical prostatectomy and have peripheral zone hypoechoic cancers the combination of ultrasound contact length and PSA value is the best predictor of extraprostatic extension.