Recurrent MEIS1 - NCOA2/1 fusions in a subset of low-grade spindle cell sarcomas frequently involving the genitourinary and gynecologic tracts

Sarcomas with MEIS1 - NCOA2 fusions have been so far reported in 2 cases each of primitive renal sarcomas and intraosseous pelvic rhabdomyosarcomas. Their histologic spectrum, anatomic distribution, and clinical behavior remain poorly defined. In this study, we report 6 additional spindle cell sarcomas with MEIS1 - NCOA2 or NCOA1 fusions that fall into the same disease spectrum with the previously reported renal sarcomas. The patients’ age range was wide (20–76 years, mean 46) and all except one were female. The tumors arose in the kidney ( n = 2), and one each in the uterine corpus, vagina, scrotum, and para-rectal region. The consistent morphology was that of monomorphic spindle to ovoid cells in a storiform, whorling, or solid pattern. Alternating cellularity, myxoid stroma, and microcystic changes were seen in some cases. Mitotic activity varied greatly (<1–33/10 high power fields). The immunophenotype was nonspecific, with most cases expressing variable degrees of TLE1, WT1, cyclin D1, CD56, and CD10. Using various platforms of RNA-based targeted sequencing, MEIS1 - NCOA2 fusions were recurrently identified in 5 cases, and a novel MEIS1 - NCOA1 fusion was found in one renal tumor. The gene fusions were validated by fluorescence in situ hybridization using custom BAC probes. Of the 5 patients with available follow-up (5 months to 8 years), all experienced local recurrences, but no distant spread or death from disease. Our results expand the clinicopathologic spectrum of sarcomas with MEIS1 - NCOA2/1 fusions, providing evidence of an undifferentiated spindle cell phenotype with nonspecific immunoprofile and low-grade clinical behavior.