Claudia Regina Ball

Rare cancers are individually uncommon but collectively represent a substantial share of cancer burden, with limited systemic treatment options for many entities. Molecular profiling identifies targetable alterations, but actionable findings are limited and responses can vary despite a matched target. This motivates complementary approaches that directly assess tumor drug response. Here, we establish a biopsy-compatible ex vivo drug sensitivity testing platform optimized for low input and reproducibility. Patient-derived material was tested either directly or following ex vivo expansion. Functional profiling was performed within clinically relevant timelines across models from 126 patients with rare advanced solid tumors. Drug responses were consistent between model types. In most samples, we identified at least one potentially active compound, supporting feasibility at biopsy-scale. High in vitro sensitivity was associated with clinical benefit and progression-free survival. These findings support functional drug sensitivity testing as a complementary component in precision oncology for adults with rare cancers. Statement of Significance: This study presents a biopsy-compatible drug sensitivity testing platform for phenotype-based therapy stratification in rare cancers. It identifies actionable ex vivo drug responses and shows associations with clinical outcome in patients treated with screened therapies. These findings support functional testing as a complementary additional layer of stratification for therapeutic prioritization.

Precision oncology is becoming a mainstay in the standard of care for cancer patients. Recent technological advancements have significantly lowered the cost of various tumor profiling approaches, broadening the reach of molecular diagnostics and improving patient access to precision oncology. In parallel, drug development and discovery pipelines continue to evolve, driving targeted therapeutic options forward. Yet, not all patients harboring actionable molecular alterations respond to these interventions, and existing therapies do not cover the entire spectrum of potential molecular targets. In this review, we examine the current suite of omics technologies employed in clinical settings and underscore their roles in deepening our understanding of tumor biology and optimizing patient stratification for targeted treatments. We also highlight relevant precision oncology trials and share our own experiences using multi-omics data within a molecular tumor board framework. Finally, we discuss areas for future exploration aimed at propelling precision oncology to new heights.

Applying CAR T-cell therapy to treat solid tumors is especially challenging due to the immunosuppressive tumor microenvironment (TME). While our modular RevCAR system enhances the safety and controllability of CAR T-cell therapy, effectively targeting solid tumors remains difficult. Since PD-L1 is an immune checkpoint frequently upregulated by cancer cells and their microenvironment, it is a relevant target for solid tumors. Here, we introduce a novel PD-L1 RevTM capable of redirecting RevCAR T-cells to specifically target and kill PD-L1-expressing tumor cells, becoming activated and secreting pro-inflammatory cytokines. This is shown in vitro with monolayer and 3D models, including patient-derived cultures, and in vivo. Furthermore, we demonstrate in vitro and in vivo an AND-gated targeting of cells simultaneously expressing PD-L1 and another tumor-associated antigen by the Dual RevCAR system. Our findings suggest that RevCAR-mediated targeting of PD-L1 could be a promising therapeutic approach for modulating the TME and improving solid tumor treatment.

In-frame BRAF exon 12 deletions are increasingly identified in various tumor types. The resultant BRAF ^Δβ3-αC oncoproteins usually lack five amino acids in the β3-αC helix linker and sometimes contain de novo insertions. The dimerization status of BRAF ^Δβ3-αC oncoproteins, their precise pathomechanism, and their direct druggability by RAF inhibitors (RAFi) has been under debate. Here, we functionally characterize BRAF ^ΔLNVTAP>F and two novel mutants, BRAF ^delinsFS and BRAF ^ΔLNVT>F , and compare them with other BRAF ^Δβ3-αC oncoproteins. We show that BRAF ^Δβ3-αC oncoproteins not only form stable homodimers and large multiprotein complexes but also require dimerization. Nevertheless, details matter as aromatic amino acids at the deletion junction of some BRAF ^Δβ3-αC oncoproteins, e.g., BRAF ^ΔLNVTAP>F , increase their stability and dimerization propensity while conferring resistance to monomer-favoring RAFi such as dabrafenib or HSP 90/CDC37 inhibition. In contrast, dimer-favoring inhibitors such as naporafenib inhibit all BRAF ^Δβ3-αC mutants in cell lines and patient-derived organoids, suggesting that tumors driven by such oncoproteins are vulnerable to these compounds.