Ribociclib, a cyclin-dependent kinase (CDK) 4/6 inhibitor, is widely used in combination with endocrine therapy for advanced hormone receptor–positive breast cancer. However, drug exposure may be highly variable in older patients due to organ dysfunction and polypharmacy, raising the need for therapeutic drug monitoring (TDM). We report the case of an 88-year-old woman with metastatic lobular breast carcinoma treated with ribociclib and tamoxifen, who developed progressive renal impairment and was co-prescribed apixaban. Serial TDM demonstrated ribociclib overexposure (Cmin 1022–1318 ng/mL vs. 500 ng/mL expected at steady state), associated with markedly increased plasma concentrations of tamoxifen, endoxifen, and apixaban (923 ng/mL vs. reference peak 206 ng/mL). Monte Carlo simulations incorporating patient covariates confirmed that measured ribociclib concentrations exceeded predicted distributions, likely due to the accumulation of uremic toxins. TDM of CDK4/6 inhibitors provides valuable insight into drug exposure in complex geriatric oncology settings. Beyond monitoring ribociclib itself, this approach facilitates a broader discussion on individualized dosing, comedication safety, and management of organ dysfunction in elderly patients with cancer.
Nivolumab is approved for the treatment of advanced non-small cell lung cancer (aNSCLC) after prior chemotherapy. The Lung Initiative on Sequence Therapy (LIST) study evaluated long-term outcomes, safety and feasibility of immunotherapy rechallenge in French patients with previously treated aNSCLC in routine practice. We report the results of the final 24-month analysis. LIST was a longitudinal, prospective, observational study enrolling patients with aNSCLC who had received ≥ 1 prior line of therapy and were initiating treatment with nivolumab. Patients were classified into three cohorts according to prior immunotherapy exposure: immunotherapy-naïve (cohort 1); immunotherapy-experienced and discontinued prior immunotherapy for reasons other than immunotherapy-related toxicity (cohort 2); and discontinued because of immunotherapy-related toxicity (cohort 3). The primary endpoint was time to treatment discontinuation (TTD). Secondary endpoints included overall survival (OS), progression-free survival (PFS), response at 24 months, safety and quality of life (QoL). A total of 522 patients were included (cohort 1, n = 280; cohort 2, n = 197; cohort 3, n = 45). Median TTD was 3.8, 3.2 and 3.4 months in cohorts 1, 2 and 3, respectively, with 24-month discontinuation-free rates of 7.9
LBA4 Background: ESR1 mutations ( ESR1 m) constitutively activate the estrogen receptor (ER) and are the most common mechanism of acquired resistance to aromatase inhibitor (AI) + CDK4/6i. Molecular monitoring by ctDNA analysis can detect the emergence of ESR1 m during 1L AI + CDK4/6i. Camizestrant, the next-generation selective ER degrader (SERD) and complete ER antagonist, has shown anti-tumor activity in pts with and without detectable ESR1 m. SERENA-6 is the first global registrational Phase 3 trial assessing a ctDNA-guided approach to detect the emergence of ESR1 m during 1L AI + CDK4/6i to inform a switch in therapy ahead of disease progression. Methods: Pts with HR+/HER2– ABC who had received ≥6 months of 1L AI (anastrozole/letrozole) + CDK4/6i (abemaciclib/palbociclib/ribociclib) were enrolled and had ctDNA tested for ESR1 m every 2–3 months, coinciding with routine imaging. At ESR1 m detection, pts without evidence of disease progression were randomized 1:1 to switch to camizestrant (75 mg) with continued CDK4/6i (type and dose maintained) + placebo for AI vs continuing AI + CDK4/6i + placebo for camizestrant. The primary endpoint was investigator-assessed PFS (per RECIST v1.1). Prespecified interim analysis data cutoff was Nov 28, 2024. Results: 3,256 eligible pts were surveilled for ESR1 m using ctDNA until 315 eligible pts were randomized to switch to camizestrant (n=157) or continue with AI (n=158). All pts remained on the same CDK4/6i. ~50% of randomized pts had ESR1 m detected at the first ctDNA test. Baseline characteristics were well balanced between treatments. After 171 PFS events, hazard ratio for PFS was 0.44 (95% CI 0.31–0.60, p<0.00001; median PFS 16.0 vs 9.2 months). PFS benefit was consistent across subgroups. PFS rate at 12 months was 60.7% (95% CI 51.1–69.0) vs 33.4% (95% CI 24.9–42.2) and at 24 months was 29.7% (95% CI 19.0–41.2) vs 5.4% (95% CI 0.7–18.2). PFS2 hazard ratio was 0.52 (95% CI 0.33–0.81; 27% maturity). OS is immature (12%). Camizestrant + CDK4/6i was well tolerated with safety consistent with the known profiles of camizestrant, and of each CDK4/6i. Rates of treatment discontinuation due to adverse events were 1.3% for camizestrant and 1.9% for AI. Conclusions: Camizestrant + CDK4/6i guided by emergence of ESR1 m during 1L AI + CDK4/6i in pts with HR+/HER2– ABC resulted in a statistically significant and clinically meaningful improvement in PFS. SERENA-6 is the first global Phase 3 trial to demonstrate clinical utility of using ctDNA to detect and treat emerging resistance, ahead of disease progression. These findings represent a potential new treatment strategy to optimize and improve 1L patient outcomes. Clinical trial information: NCT04964934 .
The co-occurrence of germline and somatic oncogenic alterations is frequently observed in breast cancer, yet their combined influence on tumour evolution and therapy resistance remains poorly defined. Through an integrated clinicogenomic analysis of more than 5,800 patients, we show that germline (g) pathogenic variants dictate the evolutionary trajectory of acquired resistance. We specifically find that gBRCA2-associated tumours are uniquely predisposed to develop acquired RB1 loss-of-function alterations, resulting in poor outcomes on standard-of-care frontline CDK4/6 inhibitor (CDK4/6i) combinations. This vulnerability is driven by a dual mechanism: baseline RB1 hemizygosity (heterozygous loss resulting in a single functional RB1 allele), which lowers the evolutionary barrier to biallelic inactivation, and ongoing homologous recombination deficiency, which promotes acquisition of RB1 loss-of-function alterations under the selective pressure of CDK4/6i. Preclinical models from gBRCA2 carriers showed near-uniform resistance to CDK4/6i, with consistent post-treatment Rb loss. Across multiple independent models and in our clinical data, PARP inhibition consistently outperformed CDK4/6i. Our findings suggest that prioritizing PARP inhibition in gBRCA2 carriers may intercept RB1-loss trajectories and delay resistance. More broadly, we establish a predictive framework for forecasting drug-resistant trajectories based on pre-treatment allelic configuration and mutational signatures.
BACKGROUND:Diffuse gastric cancer (DGC) is the most common manifestation in germline CTNNA1 variant carriers, with one study estimating a 49-57% lifetime risk by age 80. Knowledge on CTNNA1-associated hereditary diffuse gastric cancer (HDGC), loss-of-function mechanisms, variant-type causality, disease spectrum and cancer risks remains scarce. OBJECTIVE:Explore CTNNA1 genotype-phenotype associations to improve genetic testing criteria, surveillance and risk-reduction recommendations for carriers. DESIGN:Using molecular, clinical and population data from 1308 individuals from 351 CTNNA1-variant carrier families and 37 428 non-carriers from European and American ancestries, we analysed genotype-phenotype associations with multivariable logistic regression. With CRISPR/Cas9 CTNNA1-knockout gastric cancer (GC) cells and CTNNA1-humanised Drosophila, we assessed CTNNA1-associated loss-of-function mechanisms. RESULTS:CTNNA1-truncating transcripts are degraded by nonsense-mediated mRNA decay (NMD), and DGCs from germline CTNNA1-truncating carriers lose αE-catenin. These transcripts are non-functional in Drosophila, in contrast to non-truncating transcripts. DGC risk is eightfold higher in truncating, compared with non-truncating carriers. The risk of GC and lobular breast cancer (LBC) development in CTNNA1-truncating variant carriers is fivefold and eightfold lower than in CDH1 pathogenic/likely pathogenic variant carriers, respectively. Compared with wild-type individuals, GC risk is 7-fold higher in CTNNA1-truncating and 38-fold higher in CDH1-truncating variant carriers. LBC is recurrent among CTNNA1-truncating carriers, some lacking HDGC criteria. Simplification of previous criteria for CTNNA1 genetic testing produced the 'Porto' criteria, which increased CTNNA1-carrier families' pick-up rate by 9%, without performance loss compared with the HDGC 2020 clinical guidelines. Macular dystrophy patterned-2 was positively associated with non-truncating variants, specifically in the αE-catenin M-fragment. CONCLUSION:We provide compelling evidence supporting that CTNNA1-truncating variants positively associate with DGC and LBC, and NMD as the pathophysiological mechanism leading to CTNNA1 downregulation. We demonstrate that compared with CDH1, CTNNA1 is a moderate penetrance HDGC gene. This new knowledge is essential to define surveillance and/or prophylactic measures for CTNNA1-carrier individuals and families.
