p27Kip1 V109G as a biomarker for CDK4/6 inhibitors indication in hormone receptor-positive breast cancer

CDK4/6 inhibitors benefit a minority of patients who receive them in the breast cancer adjuvant setting. p27Kip1 is a protein that inhibits CDK/Cyclin complexes. We hypothesized that single-nucleotide polymorphisms that impaired p27Kip1 function could render patients refractory to endocrine therapy but responsive to CDK4/6 inhibitors, narrowing the patient subpopulation that requires CDK4/6 inhibitors. We found that the p27Kip1 V109G single-nucleotide polymorphism is homozygous in approximately 15% of hormone-positive breast cancer patients. Polymorphic patients experience rapid failure in response to endocrine monotherapy compared with wild-type or heterozygous patients in the first-line metastatic setting (progression-free survival: 92 vs 485 days, P < .001); when CDK4/6 inhibitors are added, the differences disappear (progression-free survival: 658 vs 761 days, P = .92). As opposed to wild-type p27Kip1, p27Kip1 V109G is unable to suppress the kinase activity of CDK4 in the presence of endocrine inhibitors; however, palbociclib blocks CDK4 kinase activity regardless of the p27Kip1 status. p27Kip1 genotyping could constitute a tool for treatment selection.

Abstract P6-01-46: Independent validation of the HER2DX genomic test in HER2-positive breast cancer treated with neoadjuvant docetaxel, carboplatin, trastuzumab +/- pertuzumab (TCH/TCHP): a correlative analysis from a multicenter academic study

Background: HER2DX (Prat et al. EBiomedicine 2022) is a 27-gene prognostic (risk-score) and predictive (pathological complete response [pCR]-score) assay in early-stage HER2+ breast cancer based on clinical data and the expression of 4 gene signatures (immune, proliferation, luminal differentiation and HER2 amplicon). Here, we aim to evaluate, for the first time, the ability of HER2DX to predict pCR following neoadjuvant TCH or TCHP in HER2+ disease. Methods: Standardized HER2DX was performed in a central lab on baseline pre-treatment FFPE tumor biopsies from the GOM-HGUGM-2018-05 study in Spain, a consecutive retrospective series of patients (pts) with newly diagnosed stage I-III HER2+ breast cancer eligible for neoadjuvant therapy. Pts received standard 6 cycles of docetaxel, carboplatin and trastuzumab (TCH) or TCH with pertuzumab (TCHP) regimens. Primary aim was to test the ability of HER2DX pCR score to predict pCR (ypT0/is ypN0). Secondary objectives were to test the ability of HER2DX pCR score to predict pCR independently of clinical-pathological variables and the PAM50 subtype (HER2-enriched versus not), and to evaluate the association of HER2DX pCR score with the HER2DX risk-score. Logistic regression and receiver-operator curve (ROC) analysis were assessed. Statistical analyses were performed in R code 4.0.5. Results: HER2DX was evaluated in 155 pts (97%) enrolled in the study with available RNA (as of June 2022). Mean age of pts was 50 (range 22-74) and 55.2% of pts (n=85) were pre-menopausal. Clinical T2-4 disease represented 77.4% of cases (n=120), clinical node-positive disease (cN1-3) represented 63.9% of cases (n=99), and 68.0% of tumors (n=105) were hormone receptor-positive. The overall pCR rate was 57.4% (95% confidence interval [CI] 50-65): 52.2% (95% CI 40-64) with TCH (n=67) and 61.4% (95% CI 50-72) with TCHP (n=88). The proportion of HER2DX low-, medium- and high-pCR groups was 34.2%, 34.8% and 31.0%, respectively. HER2DX pCR score (as a continuous variable from 0 to 100) was significantly associated with pCR (odd ratio [OR]=1.03, p=5.91e-07). The pCR rates in HER2DX pCR-high and pCR-low groups were 75.0% and 28.0% (OR=7.6, 95% CI 3.2-19.1, p=7.14e-06), respectively. In pts treated with TCHP, the pCR rates in HER2DX pCR-high and pCR-low groups were 85.7% and 27.3% (OR=16.0, 95% CI 4.3-59.01, p=3.2e-05), respectively. The AUC ROC of HER2DX pCR score (as a continuous variable) and pCR status was 0.746 (in all pts) and 0.812 (in pts treated with TCHP). HER2DX pCR score was significantly associated with pCR independently of hormone receptor status, Ki67, age, menopausal status, pertuzumab use, clinical stage and PAM50 HER2-enriched subtype. The proportion of HER2DX low- and high-risk of relapse disease was 32.0% and 68.0%, respectively. The correlation of HER2DX pCR score and HER2DX risk-score was weak (coefficient=-0.17), as previously described. Proportion of cases according to both HER2DX scores and absolute difference of pCR rates between TCHP and TCH in each combined group is shown in Table. Conclusion: The HER2DX genomic test predicts pCR following neoadjuvant TCH or TCHP regimens independently of clinical-pathological variables and intrinsic subtype. The combination of both HER2DX scores might help better tailor systemic therapy in patients with newly diagnosed stage I-III HER2+ breast cancer.

Citation Format: Coralia Bueno-Muiño, Isabel Echavarria, Sara López-Tarruella, Roche-Molina Marta, María del Monte-Millán, Tatiana Massarrah, Yolanda Jerez Gilarranz, Blanca Herrero, Salvador Gámez, Iván Márquez-Rodas, María Cebollero-Presmanes, Nevado Santos Manuel, Pilar de la Morena Barrio, Francisco Ayala de la Peña, José Ángel García-Sáenz, Fernando Moreno Antón, Álvaro Rodríguez Lescure, Teresa Quintanar, Diego Malón-Giménez, Laura Rodriguez-Lajusticia, Ana Isabel Ballesteros García, Dulce Bañón Torres, Lucía Villarejo, Nerea Lobato, Ainhoa Arias, Inmaculada Ocaña, Enrique Álvarez, Laia Paré, Mercedes Marín-Aguilera, Patricia Galván, Fara Brasó-Maristany, Ana Vivancos, Patricia Villagrasa, Joel S Parker, Charles M. Perou, Aleix Prat, Miguel Martín. Independent validation of the HER2DX genomic test in HER2-positive breast cancer treated with neoadjuvant docetaxel, carboplatin, trastuzumab +/- pertuzumab (TCH/TCHP): a correlative analysis from a multicenter academic study [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P6-01-46.