Background: Uterine leiomyosarcoma (uLMS) are rare and malignant tumors that arise in the myometrium cells and whose diagnosis is based on histopathological features. Identifying diagnostic biomarkers for uLMS is a challenge due to molecular heterogeneity and the scarcity of samples. In vivo and in vitro models for uLMS are urgently needed. Knockout female mice for the catalytic subunit of the immunoproteasome PSMB9 (MIM:177045) develop spontaneous uLMS. This study aimed to analyze the role of PSMB9 in uLMS tumorigenesis and patient outcome. Methods: Molecular data from 3 non-related uLMS cohorts were integrated and analyzed by proteotranscriptomic using gene expression and protein abundance levels in 68 normal adjacent myometrium (MM), 66 uterine leiomyoma (LM), and 67 uLMS. Results: the immunoproteasome pathway is upregulated and the gene PMSB9 shows heterogeneous expression values in uLMS. Quartile group analysis showed no significant difference between groups high and low PSMB9 expression groups at 3-years overall survival (OS). Using CYBERSORTx analysis we observed 9 out of 17 samples in the high group clustering together due to high M2 macrophages and CD4 memory resting, and high CD8+/PSMB9 ratio was associated with better OS. The main pathway regulated in the high group is IFNγ and in the low is the ECM pathway dependent on the proto-oncogene SRC. Conclusion: these findings suggest 2 subtypes of uLMS (immune-related and ECM-related) with different candidate mechanisms of malignancy.

The onset of immune checkpoint blockade (ICB) therapy over the last decade has transformed the therapeutic landscape in oncology. ICB has shown unprecedented clinical activity and durable responses in a variety of difficult-to-treat cancers. However, despite these promising long-term responses, a majority of patients fail to respond to single-agent therapy, demonstrating primary or acquired resistance. Uterine leiomyosarcoma (uLMS) is a rare high-risk gynecological cancer with very limited treatment options. Despite research indicating a strong potential for ICB in uLMS, a clinical trial assessing the response to immunotherapy with single-agent nivolumab in advanced-stage uLMS showed no clinical benefit. Many mechanisms of resistance to ICB have been characterized in a variety of tumor types, and many more continue to be uncovered. However, the mechanisms of resistance to ICB in uLMS remain largely unexplored. By elucidating and targeting mechanisms of resistance, treatments can be tailored to improve clinical outcomes. Therefore, in this review we will explore what is known about the immunosuppressive microenvironment of uLMS, link these data to possible resistance mechanisms extrapolated from other cancer types, and discuss potential therapeutic strategies to overcome resistance.

Cancer cells can acquire a reversible, dormant drug-tolerant persister state mimicking embryonic diapause to evade therapy pressure. Deciphering the precise mechanisms driving cancer cells into or out of a diapause-like persister cell state could provide strategies to overcome resistance. In this study, we showed that following chemotherapy, diverse therapeutic agents converge on WNT pathway activation to induce a de novo diapause-like cell state across various triple-negative breast cancer cell line, xenograft, and patient-derived organoid models. Among early persister cells, only transcriptionally WNT-active persisters exhibited the transcriptional and functional characteristics typical of diapause-like cells, including a negative correlation with MYC transcriptional activity and reversible restricted proliferation. The WNT signaling pathway functioned as both an inducer and biomarker of the diapause-like early persister cell state in both parental (chemotherapy-naïve) and chemotherapy-treated cells. Entry into and exit from the diapause-like early persister cell state was triggered by the transcriptional upregulation of components essential for canonical WNT ligand secretion. A combinatorial treatment strategy inhibiting WNT ligand secretion alongside chemotherapy effectively targeted the early mechanisms underlying the acquisition and enrichment of a diapause-like cell phenotype. These findings reveal WNT pathway activation as an early event that leads to a reversible diapause-like persister state and highlight the potential of targeting this axis to prevent the development of drug-resistant populations before they are firmly established. Significance: WNT signaling is a crucial driver and biomarker of a reversible, dormant, diapause-like persister state in breast cancer cells, offering insights that could transform therapeutic strategies to disrupt tumor persistence.

The efficacy of chemotherapy is often hindered by the enrichment of a population of cancer cells that enter a drug-tolerant persister (DTP) state, mimicking embryonic diapause, yet the underlying mechanisms of this transition remain poorly understood. This study demonstrates that both parental and chemotherapy-induced Wnt-active (Wnt ^High ) cells in Triple-negative breast cancer exhibit transcriptional and functional properties characteristic of DTP cells, including a diapause transcriptional signature, reduced MYC expression, reversible restricted proliferation, and pronounced chemoresistance. Our findings reveal that the de novo activation of the Wnt signaling pathway, triggered by the transcriptional upregulation of components essential for canonical Wnt ligand-secretion and -activation, is critical for enriching the diapause-DTP (DTP ^Diap ) population across various chemotherapy regimens. The diapause-DTP/Wnt ^High population can be selectively ablated by concomitant, rather than sequential, pharmacological inhibition of Wnt ligand-secretion alongside chemotherapy, highlighting new vulnerabilities in DTP ^Diap cell-emergence and potentially yielding a therapeutic opportunity against DTPs. This study shows that activation of Wnt signaling pathway is sufficient and necessary for the induction of a DTP ^Diap state and enhances our understanding of the introductory mechanisms driving DTP cell-enrichment upon chemotherapy.