Patients with uterine leiomyosarcoma (LMS) typically present with vaginal bleeding, pain, and a pelvic mass, with atypical presentations of hypercalcemia and eosinophilia also being reported. Radiographic evaluation with combined positron-emission tomography/computed tomography may assist in diagnosis and surveillance in women with uterine LMS; these are commonly used with stage and tumour grade as prognostic indicators and a recently developed risk-assessment index to predict disease-specific survival. Recent studies have shown that the addition of adjuvant therapy after surgical management does not seem to improve survival, and ovarian preservation does not appear to negatively impact outcome. Experimentally, it is noteworthy that proteasome subunit beta 9 (PSMB9)/beta 1i-deficient mice exhibit spontaneous development of uterine LMS, with a disease prevalence of similar to 37% by 12 months of age. Furthermore, a recent report showed the loss of ability to induce PSMB9/beta 1i expression, that is up-regulated by interferon-gamma (IFN gamma), in human uterine LMS tissues. Here, we reviewed human uterine LMS for genetic mutations in the IFN gamma signal cascade, and found serious mutations in three genes, Janus activated kinase 1 (JAK1), signal transducer and activator of transcription 1 (STAT1) and PSMB9/beta 1i promoter regions. Moreover, molecular experiments demonstrated differential expression of cyclin E and P27/KIP1, that regulate cell-cycle G1 arrest via PSMB9/beta 1i expression. The discovery of this mutational activation of a key cell-signalling pathway may provide new targets for diagnostic approaches and therapeutic intervention.