[853] Solid Pattern of Testicular Yolk Sac Tumor: A Morphologic and Immunohistochemical Study of 52 Cases.

Chia-Sui Kao, Muhammad T Idrees, Robert H Young, Thomas M Ulbright. Indiana University School of Medicine, Indianapolis; Massachusetts General Hospital & Harvard Medical School, Boston

Background: Yolk sac tumors (YST) may exhibit numerous patterns, including microcystic/reticular, papillary, glandular, and solid. The solid pattern is prone to misinterpretation, particularly in small biopsy specimens, as other testicular neoplasms, most commonly seminoma. Distinguishing solid pattern YST from seminoma is of critical importance since they are treated differently.
Design: 52 cases of solid YST were confirmed by reviewing H&E stained sections. A solid pattern was defined as a sheet-like arrangement that could have rare foci of microcysts and that occupied more than 2 mm2. The following features were assessed: cytoplasmic quality, associated YST patterns, necrosis, lymphocytic infiltrate, hyaline globules, intercellular basement membrane deposits, microcysts, sinusoidal vascularity, myxoid background, degree of nuclear pleomorphism and an appliqué pattern. Immunohistochemical stains were performed on 36 cases and evaluated by a modified Allred scoring method for proportion and intensity of positivity.
Results: Solid YST was mostly comprised of sheets of cells with abundant pale to clear cytoplasm (85%) and almost always (98%) associated with other patterns, most commonly microcystic/reticular (75%), glandular (35%) and myxoid (25%). Intercellular basement membrane (75%), focal microcysts (67%), significant nuclear pleomorphism (65%) and hyaline globules (65%) were common, whereas a myxoid background (39%), lymphocytic infiltrate (17%) and an appliqué pattern (8%) were less frequent. AE1/AE3 cytokeratin and glypican 3 provided the most intense and diffuse staining of solid YST, whereas AFP was negative in 38%. CD117 stained 59% whereas podoplanin was positive in only 1 case (3%) and OCT3/4 was uniformly negative.
Conclusions: Solid YST can generally be recognized by careful morphologic evaluation, especially its association with other patterns, the presence of band-like deposits of basement membrane, occasional microcysts, nuclear pleomorphism and intracellular hyaline globules and usual absence of lymphocytes. In difficult cases an immunohistochemical panel including AE1/AE3, glypican 3, OCT3/4 and podoplanin aids in its distinction from other neoplasms. Frequent positivity of solid YST for CD117 indicates it has little value in the differential diagnosis with seminoma. AFP stains are commonly negative or weak and focal and should not solely be relied on for diagnosis.
Category: Genitourinary (including renal tumors)

Tuesday, March 1, 2011 8:45 AM

Platform Session: Section A, Tuesday Morning


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