Genomic and Histologic Analysis of Uterine Leiomyosarcoma from Leiomyoma with Bizarre Nuclei

Leiomyoma with bizarre nuclei (LM-BN) is a rare variant of leiomyoma with a benign clinical course. In contrast, leiomyosarcoma (LMS) is a high-grade, malignant neoplasm characterized by high recurrence rates and poor survival. While LM-BN and LMS show distinct morphologies, they share similar immunoprofile and molecular alterations, with both considered “DNA unstable”. Rare cases of LM-BN associated with LMS have been reported, however the histogenesis and molecular relationship between these two tumors remains unclear. In this study, we assessed 11 cases of LMS arising in conjunction with LM-BN and further analyzed the clinical, histologic, and molecular characteristics of these lesions. Tumor slides were examined by histology and immunohistochemistry to confirm the presence of both LMS and LM-BN components. LM-BN and LMS had similar p16 and p53 IHC patterns, but LMS had a higher Ki-67 index and lower ER/PR expression. Digital image analysis based on nuclear and cytologic features revealed spatial relationships between LMS and LM-BN. Genomic copy number alteration (CNA) demonstrated the same clonal origin of LMS from existing LM-BN through conserved copy number alterations. LMS harbored higher CNAs and frequent loss of the TP53, Rb, PTEN, and/or CDKN2A genomic region than LM-BN, indicative of tumor progression. Spatial transcriptome analysis defined uniquely expressed gene signatures in a geographical distribution, demonstrating molecular evidence of regional cell specific differences of LM-BN and LMS. Mutation analysis of large oncogenic panel revealed many shared functional gene alterations in both LM-BN and LMS, but more highly enriched in LMS. Our findings for the first time suggest that a subset of LMS arise from an existing LM-BN. Overall design: Four cases with the best distributions of both LMS and LM-BN back-to-back within 6x6mm regions were selected for spatial transcriptomic RNA-seq. To confirm the RNA quality of each FFPE tissue block, 1-2 curls (10um thickness each) were used for RNA extraction using Qiagen RNeasy FFPE kit (Qiagen 73504) according to manufactures' protocol. Extracted RNA was examined by Agilent Bioanalyzer RNA pico chip to confirm the DV200 >30%. Simultaneously, the tissue morphology was examined on H&E-stained slide to identify the presence of both LMS and LM-BN components.