[718] CDX2 Expression in Yolk Sac Tumor of Testicular Origin

Z Bing, T Pasha, JE Tomaszewski, P Zhang. Hospitial of University of Pennsylvania, Philadelphia, PA

Background: The degree and direction of the differentiation determine the histologic subtype of germ cell tumors. Yolk sac tumor (YST) shows extraembryonic differentiation and is usually a component of mixed germ cell tumors albeit rare pure YST can occur especially in metastasis. YST can show a variety of growth patterns and can mimic adenocarcinomas. CDX2 is a caudal-related transcription factor that is expressed in normal and neoplastic epithelium of intestine. Although CDX2 reactivity has been found in rare tumors of urinary bladder, prostate, lung, pancreas and ovary, it has been used as diagnostic marker of tumors of intestinal origin. However, CDX2 reactivity in testicular germ cell tumors of various subtypes has not been evaluated.
Design: Only testicular germ cell tumors were evaluated to exclude any possible CDX2+ non-germ cell tumors. There were 29 cases available, 13 with components of seminoma, 9 embryonal carcinoma, 8 YST, 1 case of immature teratoma , and 2 mature teratoma with one having mature colonic mucosa. 7 of the 29 cases also contained intratubular germ cell neoplasia unclassified (ITGCNU). Immunohistochemistry for CDX2 (clone CDX2-88, 1:10, Biogenex Laboratories, San Ramon, CA) was performed on paraffin sections using Leica Microsystems' Bond IHC staining platform. Nuclear staining was scored as negative (<1% of cell staining), 1+ (1% to 25%), and 2+ (>25%).
Results: 5 out of 8 (62.5%) YST were positive for CDX2 immunostaining, in which 3 showed 1+ positivity and two 2+ positivity. The staining pattern in some cases was notable for nuclear positivity in discrete clusters of malignant glands with intervening negative malignant glands. Others showed positive cells scattered in the tumor. One of the two cases with strongest stain resembled a well differentiated endometrioid adenocarcinoma without overt colorectal morphology. Mature colonic muscosa in one of the mature teratomas was positive for CDX2. No CDX2 immunostains were detected in ITGCNU, seminoma, embryonal carcinoma, and immature teratoma.
Conclusions: Testicular YST can show CDX2 nuclear positivity in a patchy or scattered fashion while other primitive components of germ cell tumor are negative. Although our study is confined to tumors of testicular origin, it is likely that YST of other sites would express CDX2 as well. YST should be included in the differential diagnosis of gland-forming tumors of unknown origin with CDX2 positivity, especially when the patient is relatively young, outside the gonads as metastasis from gonade or a primary.
Category: Genitourinary (including renal tumors)

Monday, March 9, 2009 1:00 PM

Poster Session II # 100, Monday Afternoon