Diagnosis of Prostate Cancer in Needle Biopsies After Radiation Therapy

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Abstract
Interpretation of postirradiation needle biopsies is a major diagnostic challenge for the pathologist because of substantial radiation-induced changes in benign and malignant prostatic tissue. Reports that have systematically evaluated the histopathologic findings in postirradiation needle biopsies are limited. In this study, we evaluated 46 histologic features in 29 postirradiation needle biopsy specimens from 29 patients. All patients had recurrent cancer on needle biopsies after external beam radiation, and all subsequently underwent salvage radical prostatectomy and bilateral pelvic lymphadenectomy. Patient age ranged from 57 to 78 years (mean, 61 years). The interval from radiation therapy to biopsy ranged from 1.0 to 17 years (mean, 3.9 years). Histologic features that were helpful in the diagnosis of cancer after radiation therapy included infiltrative growth, perineural invasion, intraluminal crystalloids, blue mucin secretions, the absence of corpora amylacea, and the presence of coexistent high-grade prostatic intraepithelial neoplasia. Benign glands usually showed nuclear enlargement (86%) and prominent nucleoli (50%), and therefore, these cytologic features alone were not reliable for the diagnosis of cancer after irradiation. Postirradiation needle biopsies underestimated the prostatectomy Gleason grade in 35% of cases and overestimated it in 14% of cases; these results were similar to published reports from patients not receiving radiation therapy. There was a major discrepancy in degree of radiation effect between radical prostatectomy and biopsies. Moderate or severe radiation effect on cancer was present in 48% of needle biopsy specimens, whereas 94% of radical prostatectomy specimens had no or minimal radiation effect on cancer when the areas with the least amount of radiation effect were chosen for quantification. These findings indicate that quantification of radiation effect in needle biopsy specimens was inaccurate and potentially misleading. Conversely, Gleason grade in postirradiation needle biopsy specimens appeared to provide useful predictive information and should be reported.