Diagnosis of prostate cancer in needle biopsies after radiation therapy

Interpretation of postirradiation needle biopsies is a major diagnostic cha llenge 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 posti rradiation needle biopsy specimens from 29 patients. All patients had recur rent cancer on needle biopsies after external beam radiation, and all subse quently underwent salvage radical prostatectomy and bilateral pelvic lympha denectomy. Patient age ranged from 57 to 78 years (mean, 61 years). The int erval 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 a mylacea, and the presence of coexistent high-grade prostatic intraepithelia l neoplasia. Benign glands usually showed nuclear enlargement (86%) and pro minent nucleoli (50%), and therefore. these cytologic features alone were n ot reliable for the diagnosis of cancer after irradiation. Postirradiation needle biopsies underestimated the prostatectomy Gleason grade in 35% of ca ses and overestimated it in 14% of cases; these results were similar to pub lished reports from patients not receiving radiation therapy. There was a m ajor discrepancy in degree of radiation effect between radical prostatectom y and biopsies. Moderate or severe radiation effect on cancer was present i n 48% of needle biopsy specimens, whereas 94% of radical prostatectomy spec imens had no or minimal radiation effect on cancer when the areas with the least amount of radiation effect were chosen for quantification. These find ings indicate that quantification of radiation effect in needle biopsy spec imens was inaccurate and potentially misleading. Conversely, Gleason grade in postirradiation needle biopsy specimens appeared to provide useful predi ctive information and should be reported.