Cooperative genomic lesions in HRAS-mutant cancers predict resistance to farnesyltransferase inhibitors.

In the clinical development of farnesyltransferase inhibitors (FTIs) for HRAS-mutant tumors, responses varied by cancer type. Co-occurring mutations may affect responses. We aimed to uncover cooperative genetic events specific to HRAS-mutant tumors and to study their effect on sensitivity to FTIs. Using targeted sequencing data from the MSK-IMPACT and Dana-Farber Cancer Institute Genomic Evidence Neoplasia Information Exchange databases, we identified comutations that were observed predominantly in HRAS-mutant versus KRAS-mutant or NRAS-mutant cancers. HRAS-mutant cancers had a higher frequency of coaltered mutations (48.8%) in the MAPK, PI3K, or RTK pathway genes, compared with KRAS-mutant (41.4%) and NRAS-mutant (38.4%) cancers (p < 0.05). Class 3 BRAF, NF1, PTEN, and PIK3CA mutations were more prevalent in HRAS-mutant lineages. To study the effects of comutations on sensitivity to FTIs, HrasG13R was transfected into "RASless" (Kraslox/lox/Hras-/-/Nras-/-/RERTert/ert) mouse embryonic fibroblasts (MEFs), which sensitized nontransfected MEFs to tipifarnib. Comutation in the form of Pten or Nf1 deletion and Pik3caH1047R transduction led to resistance to tipifarnib in HrasG13R-transfected MEFs in the presence or absence of KrasWT, whereas BrafG466E transduction led to resistance to tipifarnib only in the presence of KrasWT. Combined treatment with tipifarnib and MEK inhibition sensitized cells to tipifarnib in all settings, including in MEFs with PI3K pathway comutations. HRAS-mutant tumors demonstrate lineage-dependent MAPK or PI3K pathway alterations, which confer resistance to tipifarnib. The combined use of FTIs and MEK inhibition is a promising strategy for HRAS-mutant tumors.

RBM10 loss induces aberrant splicing of cytoskeletal and extracellular matrix mRNAs and promotes metastatic fitness.

RBM10 modulates transcriptome-wide cassette exon splicing. Loss-of-function RBM10 mutations are enriched in thyroid cancers with distant metastases. Analysis of transcriptomes and genes mis-spliced by RBM10 loss showed pro-migratory and RHO/RAC signaling signatures. RBM10 loss increases cell velocity. Cytoskeletal and ECM transcripts subject to exon-inclusion events included vinculin (VCL), tenascin C (TNC) and CD44. Knockdown of the VCL exon inclusion transcript in RBM10-null cells reduced cell velocity, whereas knockdown of TNC and CD44 exon-inclusion isoforms reduced invasiveness. RAC1-GTP levels were increased in RBM10-null cells. Mouse Hras G12V /Rbm1O KO thyrocytes develop metastases that are reversed by RBM10 or by combined knockdown of VCL, CD44 and TNC inclusion isoforms. Thus, RBM10 loss generates exon inclusions in transcripts regulating ECM-cytoskeletal interactions, leading to RAC1 activation and metastatic competency. Moreover, a CRISPR-Cas9 screen for synthetic lethality with RBM10 loss identified NFkB effectors as central to viability, providing a therapeutic target for these lethal thyroid cancers.

RAS-Mutated Cytologically Indeterminate Thyroid Nodules: Prevalence of Malignancy and Behavior Under Active Surveillance.

Background: Genomic profiling is now available for risk stratification of cytologically indeterminate thyroid nodules (ITNs). Mutations in RAS genes (HRAS, NRAS, KRAS) are found in both benign and malignant thyroid nodules, although isolated RAS mutations are rarely associated with aggressive tumors. Because the long-term behavior of RAS-mutant ITNs is not well understood, most undergo immediate surgery. In this multicenter retrospective cohort study, we characterize tumor growth kinetics of RAS-mutant ITNs followed with active surveillance (AS) using serial ultrasound (US) scans and examine the histopathologic diagnoses of those surgically resected. Methods: US and histopathologic data were analyzed retrospectively from two cohorts: (1) RAS-mutant ITNs managed with AS at three institutions (2010-2023) and (2) RAS-mutant ITNs managed with immediate surgery at two institutions (2016-2020). AS cohort subjects had ≥3 months of follow-up and two or more US scans. Cumulative incidence of nodule growth was determined by the Kaplan-Meier method and growth by ≥72% change in tumor volume. Pathological diagnoses for the immediate surgery cohort were analyzed separately. Results: Sixty-two patients with 63 RAS-mutated ITNs under AS had a median diameter of 1.7 cm (interquartile range [IQR] 1.2-2.6) at time of diagnosis. During a median AS period of 23 months (IQR 9.5-53.5 months), growth was observed in 12 of 63 nodules (19.0%), with a cumulative incidence of 1.9% (1 year), 23.0% (3 years), and 28.0% (5 years). Most nodules (81.0%) demonstrated stability. Surgery was ultimately performed in 6 nodules, of which 1 (16.7%) was malignant. In the cohort of 209 RAS-mutant ITNs triaged to immediate surgery, 33% were malignant (23.9% American Thyroid Association [ATA] low-risk cancers, 7.2% ATA intermediate-risk, and 1.9% ATA high-risk. During a median follow-up of 6.9 (IQR 4.4-7.1) years, there were no disease-specific deaths in these patients. Conclusions: We describe the behavior of RAS-mutant ITNs under AS and find that most demonstrate stability over time. Of the resected RAS-mutant nodules, most were benign; of the cancers, most were ATA low-risk. Immediate surgical resection of all RAS-mutant ITNs appears to be a low-value practice. Further research is needed to help define cases most appropriate for AS or immediate surgery.

Novel prognostic nomogram for predicting recurrence-free survival in medullary thyroid carcinoma.

AIMS: Recently, there have been attempts to improve prognostication and therefore better guide treatment for patients with medullary thyroid carcinoma (MTC). In 2022, the International MTC Grading System (IMTCGS) was developed and validated using a multi-institutional cohort of 327 patients. The aim of the current study was to build upon the findings of the IMTCGS to develop and validate a prognostic nomogram to predict recurrence-free survival (RFS) in MTC. METHODS AND RESULTS: Data from 300 patients with MTC from five centres across the USA, Europe, and Australia were used to develop a prognostic nomogram that included the following variables: age, sex, AJCC stage, tumour size, mitotic count, necrosis, Ki67 index, lymphovascular invasion, microscopic extrathyroidal extension, and margin status. A process of 10-fold cross-validation was used to optimize the model's performance. To assess discrimination and calibration, the area-under-the-curve (AUC) of a receiver operating characteristic (ROC) curve, concordance-index (C-index), and dissimilarity index (D-index) were calculated. Finally, the model was externally validated using a separate cohort of 87 MTC patients. The model demonstrated very strong performance, with an AUC of 0.94, a C-index of 0.876, and a D-index of 19.06. When applied to the external validation cohort, the model had an AUC of 0.9. CONCLUSIONS: Using well-established clinicopathological prognostic variables, we developed and externally validated a robust multivariate prediction model for RFS in patients with resected MTC. The model demonstrates excellent predictive capability and may help guide decisions on patient management. The nomogram is freely available online at https://nomograms.shinyapps.io/MTC_ML_DFS/.