[1141] Immunohistochemistry Helps To Discriminate between Symplastic Leiomyoma and Leiomyosarcoma of the Uterus

Sarah Feller, Inti Zlobec, Hana Burger, Stephan C Schaefer. University of Bern, Bern, Switzerland

Background: Symplastic (bizarre) leiomyomas of the uterus can mimic leiomyosarcoma due to its wide range of histomorphologic changes such as high cellularity, intermediate mitotic count (up to 8/10hpf) and bizarre atypical cells. When tumor necrosis is absent, discrimination between symplastic leiomyomas and leiomyosarcomas can be difficult. Discrimination between these two entities with immunohistochemical staining has been described with discordant results.
Design: A tissue microarray of 70 cases including 34 usual leiomyomas, 11 cellular leiomyomas, 9 symplastic leiomyomas and 16 leiomyosarcomas diagnosed between 1991 and 2008 was constructed. In addition to H&E and toluidine blue staining, immunohistochemistry for 14 different markers was performed, namely MCT, c-kit, LCA, MIB-1, CD10, p16, p53, bcl2, ER, PgRA, SMA, Actin, Desmin and Myoglobin. The percentage of positive stained cells was assessed and staining intensity was scored as weak (1), moderate (2) and strong (3).
Results: None of the markers separately could clearly distinguish between leiomyosarcomas and symplastic leiomyomas. Expression of PgRA and Desmin was lower by trend in leiomyosarcomas compared to the three other groups, whereas expression of p16 was higher in leiomysarcomas. The combination of a PgRA >15% and p16 expression in <50% of the neoplastic cells or the combination of PgRA in <15% and Desmin expression in > 90% can help to distinguishe between symplastic leiomyomas and leiomyosarcomas (p<0.001).
Conclusions: Tumour necrosis and a high mitotic count are still the best indicators for leiomyosarcoma compared to symplastic leiomyoma. If these indicators are absent, combination of PgRA, Desmin and p16 expression might help to distinguish between leiomyosarcoma and symplastic leiomyoma of the uterus.
Category: Gynecologic & Obstetrics

Wednesday, March 6, 2013 1:00 PM

Poster Session VI # 197, Wednesday Afternoon

 

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