Fig. 6: Acquisition of subclonal RB1 mutations as mechanism of acquired resistance to ribociclib in tumors with RB1 heterozygous loss.

A On the top, copy number and mutation status of CDKN2A, RB1, CCNE1 and CCND1 in tumors derived from PDX244, including an untreated sensitive tumor (2R) or tumors with acquired resistance to ribociclib (15L to 19R). Deep-Del (homozygous loss), CN < −1; Shallow-Del (heterozygous loss), −1 ≤ CN < −0.4; Unaltered, CN ≥ −0.4. Hashtags indicate tumors that acquired deleterious mutations in RB1. On the bottom, representative pictures showing IHC staining of p16, pRb, cyclin E1 and cyclin D1 from the indicated tumors (bottom). Dashed-red lines mark off areas with different protein staining intensity and protein score is indicated. For 19R there was no FFPE tumor available. Scale bar = 100 µm. B IHC staining of p16 and pRb in representative FFPE sections from PDX476.1 and PDX476.2. Protein score is provided. Scale bar = 100 µm. C Clinical outcome expressed in months for the indicated clinical endpoint in patients with ER⁺/HER2^-, RB1 unaltered tumors vs. those harboring tumors with RB1 heterozygous loss. Data and statistical analysis were extracted from the cBioportal. HT hormone therapy, WES whole-exome sequencing, TS targeted-sequencing, n number of patients, DFS disease-free survival, OS overall survival, DOT days of treatment. D Association between RB1 double hit alterations (concomitant mutation and deletion) and prior exposure to CDK4/6 inhibitors in metastatic BC patients (n = 582 tumors). Black square represent the logit value. Multivariable logistic regression two-tailed unadjusted p-value and the 95% confidence intervals (CI; horizontal segment represents) for the test are shown. Source data are provided as a Source Data file.