[1023] Microcystic Adenocarcinoma of the Prostate

O Yaskiv, D Cao, PA Humphrey. Washington University School of Medicine, Saint Louis, MO

Background: Cystic change in prostatic adenocarcinoma is unusual and may be confused with cystically dilated benign prostatic glands. The aim of this study was to assess histological and immunohistological characteristics of microcystic prostatic adenocarcinoma.
Design: We identified a total of 69 cases of microcystic prostatic adenocarcinoma in radical prostatectomy sections. Histological features that were evaluated include atrophic features, mitotic figures, apical snouts, nuclear and nucleolar enlargement, collagenous micronodules, perineural invasion, Gleason grade, intraluminal wispy blue mucin, intraluminal crystalloids, and amphophilic or cleared cytoplasm. The size of the microcystic and adjacent non-cystic glands was determined using an ocular micrometer. Immunohistochemistry was performed using alpha-methylacyl CoA racemase (AMACR), p63, and 34betaE12 immunostains.
Results: The incidence of microcystic change in adenocarcinoma in radical prostatectomy cases was 57 of 472, or 12.1%. The microcystic glands were typically adjacent to usual small acinar adenocarcinoma. In five cases the cystically dilated glands comprised the majority of glands in an individual focus of carcinoma. The dilated glands measured from 0.4 to 0.9 mm, being on average 10 times larger then the adjacent non-microcystic adenocarcinoma glands. Atrophic features and apical cytoplasmic snouts were common. Gleason grade of adjacent glands and the entire case ranged from grade 2 to grade 4 with grade 3 being the most common. Microcystic glands showed nodular, infiltrative, and mixed nodular-infiltrative growth patterns. In two cases, microcystic adenocarcinoma glands were seen invading into periprostatic adipose tissue. Intraluminal crystalloids, and wispy blue intraluminal mucin were seen in all cases, and amphophilic cytoplasm was present in most cases. Perineural invasion and collagenous micronodules were absent. Immunostains showed complete basal cell absence in the microcystic glands and AMACR overexpression was observed in 80% of microcystic gland cases.
Conclusions: Microcystic adenocarcinoma of the prostate is a distinctive histomorphological presentation of prostatic adenocarcinoma that is deceptively benign-appearing. Detection of intraluminal crystalloids or wispy blue mucin at low magnification, immunostains for AMACR and basal cells, and a search for adjacent usual small acinar adenocarcinoma are helpful diagnostic aids. Diagnostic awareness of this growth pattern of prostatic carcinoma is important to avoid underdiagnosis of adenocarcinoma of the prostate.
Category: Genitourinary (including renal tumors)

Tuesday, March 23, 2010 1:15 PM

Platform Session: Section A, Tuesday Afternoon


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