Diagnostic Utility of the JAZF1/JJAZ1 Gene Fusion in Endometrial Stromal Sarcomas and Their Histologic Variants

ABSTRACT

BACKGROUND: The diagnosis of endometrial stromal sarcoma (ESS) is often difficult in cases showing diverse histological differentiation or in undifferentiated endometrial sarcoma (UES). Recently, JAZF1/JJAZ1 gene fusion has been described as a defining feature of low-grade ESS (LGESS). However, its prevalence is variably reported, and the diagnostic utility has rarely been examined for cases showing various histological differentiation. METHODS: To test the diagnostic utility of JAZF1/JJAZ1 gene fusion in difficult cases, we compared the prevalence of the JAZF1/JJAZ1 fusion gene in LGESS with and without histological differentiation. RESULTS: The JAZF1/JJAZ1 fusion transcript was detected in 18 of 21 LGESS (85.7%), including 14 classical LGESS (93%), four LGESS with diverse histological differentiation (67%), and two with UES (28.6%). Positive cases included two LGESS with sex cord-like differentiation, one with osseous differentiation, and two UES. LGESS showing smooth muscle differentiation revealed the fusion transcript only in the classic area. Direct sequencing analysis of two LGESS revealed a previously reported breakpoint at t(7;17)(p15;q21). CONCLUSIONS: The JAZF1/JJAZ1 fusion gene was identified in a significant proportion of LGESS showing secondary histological differentiation except in cases with smooth muscle differentiation. Thus, this fusion gene may be useful to confirm the diagnosis in difficult cases of LGESS.