Establishment of clinically annotated, molecularly characterized, patient-derived xenografts (PDXs) from treatment-naïve and pretreated patients provides a platform to test precision genomics-guided therapies. An integrated multi-OMICS pipeline was developed to identify cancer-associated pathways and evaluate stability of molecular signatures in a panel of pediatric and AYA PDXs following serial passaging in mice. Original solid tumor samples and their corresponding PDXs were evaluated by whole-genome sequencing, RNA-seq, immunoblotting, pathway enrichment analyses, and the drug–gene interaction database to identify as well as cross-validate actionable targets in patients with sarcomas or Wilms tumors. While some divergence between original tumor and the respective PDX was evident, majority of alterations were not functionally impactful, and oncogenic pathway activation was maintained following serial passaging. CDK4/6 and BETs were prioritized as biomarkers of therapeutic response in osteosarcoma PDXs with pertinent molecular signatures. Inhibition of CDK4/6 or BETs decreased osteosarcoma PDX growth (two-way ANOVA, p < 0.05) confirming mechanistic involvement in growth. Linking patient treatment history with molecular and efficacy data in PDX will provide a strong rationale for targeted therapy and improve our understanding of which therapy is most beneficial in patients at diagnosis and in those already exposed to therapy.

Bromodomain and extraterminal (BET) domain protein family are epigenetic readers that regulate gene transcription, cell-cycle progression, and DNA damage response (DDR), making them attractive therapeutic targets for sarcomas, which are epigenetically dysregulated and genomically unstable. Sarcomas are molecularly heterogeneous with a high propensity for metastasis, resulting in poor clinical outcomes. BET inhibitors (BETi) hold promise for the treatment of sarcomas, for they block interaction of BETs with acetylated lysines, modify gene expression, and create an imbalance in transcription and replication kinetics. BETis also disrupt transcriptional programs driven by oncogenic fusion proteins found in some sarcomas. Preclinical studies demonstrate efficacy of BETis in inducing apoptosis, disrupting DDR, and reducing tumor growth, either as monotherapy or in combination with chemotherapy or other targeted agents, such as PI3K, histone deacetylases, and CHK1 inhibitors. Favorable results have been observed in clinical trials, but more studies are required to fully assess safety and efficacy as well as identify biomarkers of response and resistance. Ongoing research is focused on optimizing BETi safety and selectivity and exploring combination therapies, such as BETis with DDR inhibitors. This review summarizes the preclinical studies on BET inhibition and discusses clinical trial activity, providing insights into the potential of BETis in sarcoma therapy.

The retinoblastoma (RB) protein was the first tumor suppressor discovered and has been extensively studied for its canonical role in cell-cycle regulation. However, RB has broader noncanonical roles in DNA damage repair, chromosomal stability, apoptosis control, lineage commitment, cell differentiation and broad transcriptional regulation. Historically, RB inactivation has been associated with tumorigenesis, as well as resistance to cyclin-dependent kinase 4/6 inhibitors (CDK4/6i), leading to its investigation as a potential predictive biomarker. However, clinical data have not demonstrated that RB function reliably predicts response to CDK4/6i consistently. These discrepancies highlight the need to reconsider RB’s role in therapeutic response, as RB loss can promote replication stress, induce chromosomal instability, and lead to transcriptional reprograming, potentially generating context-specific therapeutic vulnerabilities. In this review, we examine the multifaceted biology of RB and evaluate how its loss influences responses to chemotherapy and targeted therapies. We highlight emerging strategies that exploit RB-deficient states using rational monotherapy and combination approaches. Reframing RB dysfunction from a binary biomarker to a driver of exploitable cellular vulnerabilities may inform and expand precision oncology strategies for aggressive and treatment-resistant cancers.