NATALEE Six-Year Survival Deepens but Payer and Maturity Hurdles Persist

Kisqali Demonstrates Clinically Meaningful Overall Survival in Early Breast Cancer

Novartis announced six-year follow-up results from the Phase III NATALEE trial, demonstrating positive and clinically meaningful overall survival (OS) data for Kisqali (ribociclib) plus endocrine therapy (ET) compared to ET alone. The study, conducted in the broadest population of stage II and III HR+/HER2- early breast cancer patients at high risk of recurrence, showed Kisqali plus ET reduced the risk of death by nearly 20% (HR=0.809). The invasive disease-free survival (iDFS) benefit deepened over time, increasing from 4.1% at five years to 5.3% at six years, with patients off Kisqali for a median of three years. The safety profile remained consistent, reinforcing Kisqali's long-term value and role in early breast cancer treatment.

• The six-year NATALEE analysis revealed that Kisqali plus endocrine therapy (ET) significantly reduced the risk of death by 19.1% (HR=0.809; 95% CI: 0.661-0.989) compared to ET alone in patients with HR+/HER2- early breast cancer at high risk of recurrence. This clinically meaningful overall survival benefit was consistently observed across all key subgroups, highlighting Kisqali's broad efficacy and potential to improve long-term outcomes for this patient population.
• Beyond overall survival, the trial demonstrated a deepening invasive disease-free survival (iDFS) benefit, which increased from 4.1% at five years to 5.3% at six years. This sustained benefit occurred even after patients had been off Kisqali for a median of 38 months. Furthermore, fewer patients treated with Kisqali plus ET experienced metastatic recurrence, and breast-cancer specific survival showed a ~30% reduction in risk of breast cancer-specific deaths.
• The longer follow-up confirmed Kisqali's safety profile remained consistent with previous analyses, with no new safety signals observed and low rates of secondary primary malignancies. This robust efficacy and safety profile has led to Kisqali being the only CDK4/6 inhibitor recommended by NCCN Guidelines® as Category 1 preferred for both all node-positive and high-risk node-negative HR+/HER2- early breast cancer, and achieving the highest ESMO-MCBS score (A) for eBC.

Kisqali's Long-Term OS Benefit in HR+/HER2- eBC

Hormone receptor (HR)-positive, human epidermal growth factor 2 (HER2)-negative breast cancer associates with a sustained risk of relapse over time, with women with estrogen receptor (ER)+ early breast cancer (BC) at continuing risk of relapse up to at least 15 years after diagnosis, despite being on adjuvant endocrine therapy for approximately 5 years. In a retrospective analysis using the ConcertAI Patient360 database of patients with stage II/III HR+/HER2- early breast cancer (EBC) who underwent surgery and received adjuvant endocrine therapy (ET), the risk of an invasive disease-free survival (iDFS) event was 26.1% at 5 years, rising to 45.0% at 10 years. Among patients with stage II disease, the risk of an iDFS event at 5 and 10 years was 22.7% and 40.5%, respectively; stage III 5- and 10-year risk was 40.4% and 62.9%. Patients with node-negative disease had 5- and 10-year risks of 22.1% and 36.9%, respectively; node-positive 5- and 10-year risk was 28.9% and 49.4%.

Baseline recurrence risk increasingly guides adjuvant endocrine therapy, with prognostic variability demonstrated within high-risk definitions aligned with monarchE Cohort 1 criteria. In a retrospective analysis of 989 patients with HR-positive, and HER2-negative BC who underwent surgery between January 2017 and August 2019, the 5-year iDFS rates were 94.7% (non-eligible), 88.9% (N1 + >5 cm), 83.3% (N1 + G3), and 77.3% (≥N2). Multivariate analysis identified N1 + G3 (HR 3.38), ≥N2 (HR 3.39), and neoadjuvant chemotherapy (HR 2.71) as poor prognostic factors. In the ConcertAI ET subanalysis, improved iDFS was observed with non-steroidal aromatase inhibitors (NSAI) ± ovarian function suppression vs tamoxifen ± ovarian function suppression (HR, 0.83; 95% CI, 0.69-0.98; p = 0.031).

Extended adjuvant endocrine therapy with an aromatase inhibitor (AI) after 5 years of tamoxifen further reduces the risk of recurrence in postmenopausal women, and continuing tamoxifen for 10 years has also been shown to further reduce the risk of recurrence compared with 5 years. Prognostic tools add information on late recurrence beyond 5 years, including the PAM50-based risk of recurrence (ROR) score, which was significantly prognostic by itself in years 5 to 10 and added clinically meaningful prognostic information to the Clinical Treatment Score (CTS) in all patients and all subgroups in the late follow-up period, and the GenesWell BCT score, where the 15-year distant metastasis-free survival (DMFS) rate was significantly lower in the BCT high-risk group (63.3%) than in the BCT low-risk group (93.6%). To reduce breast cancer recurrence in the early disease setting, the phase III, randomized, open-label CAMBRIA-1 and CAMBRIA-2 studies are comparing the next-generation oral selective estrogen receptor degrader (SERD) camizestrant versus standard-of-care endocrine therapy (aromatase inhibitors or tamoxifen) in patients with ER-positive/HER2-negative early breast cancer, who are at intermediate or high risk of disease recurrence, with the primary endpoint for both studies of invasive breast cancer-free survival.

NATALEE: Design, Endpoints, and Sustained Efficacy

Recent Phase III trials have expanded adjuvant options for high-risk HR+/HER2- early breast cancer by adding CDK4/6 inhibition to endocrine therapy. The monarchE trial established 2 years of abemaciclib plus endocrine therapy, while NATALEE evaluates 36 months of ribociclib plus endocrine therapy in a broad stage IIA to III population.

Kisqali's Evolving Role in HR+/HER2- eBC Treatment

The treatment landscape for high-risk hormone receptor-positive, HER2-negative (HR+/HER2-) early breast cancer (eBC) has expanded from endocrine therapy (ET) alone with tamoxifen, aromatase inhibitors (AI), and GnRH analogs to include cyclin-dependent kinases 4/6 inhibitors (CDK4/6is). Abemaciclib was approved for the adjuvant treatment of HR+/HER2- eBC in cases with positive lymph node involvement in 2022. In the open-label, phase III monarchE trial in patients with four or more positive nodes, or one to three nodes and either tumor size ≥5 cm, histologic grade 3, or central Ki-67 ≥20%, standard-of-care adjuvant ET with or without abemaciclib (150 mg twice daily for 2 years) demonstrated superior invasive disease-free survival (IDFS) versus ET alone (hazard ratio, 0.75; 95% CI, 0.60 to 0.93), with 2-year IDFS rates of 92.2% versus 88.7%, respectively, and an invasive disease-free survival (iDFS) improvement after 5 years by around 7.6% in patients with a high risk of recurrence. Ribociclib was approved based on the NATALEE trial, which randomized premenopausal/postmenopausal women and men with anatomical stage IIA (N0 with additional risk factors or N1), IIB, or III disease 1:1 to ribociclib (400 mg/day, 3 weeks on/1 week off for 36 months) plus nonsteroidal aromatase inhibitor (NSAI) (letrozole 2.5 mg/day or anastrozole 1 mg/day for 60 months) or NSAI alone. Ribociclib plus NSAI demonstrated significant iDFS benefit over NSAI alone [hazard ratio 0.749, 95% confidence interval (CI) 0.628-0.892; P = 0.0012], with 3-year iDFS rates of 90.7% (95% CI 89.3% to 91.8%) versus 87.6% (95% CI 86.1% to 88.9%), and when combined with non-steroidal AIs, ribociclib showed a significant iDFS benefit of 4.9% after 4 years in node-positive and node-negative patients with a high risk of recurrence.

In parallel, the poly (ADP-ribose) polymerase (PARP) inhibitor olaparib has been established as adjuvant therapy for 1 year in patients with BRCA germline mutation and HR+/HER2- eBC and a high risk of recurrence (CPS-EG score ≥ 3) who have been previously treated with neoadjuvant or adjuvant chemotherapy. In the phase III OlympiA trial (NCT02032823) in patients with germline BRCA1 and/or BRCA2 pathogenic variants and HER2-negative, high-risk early breast cancer, 1 year of adjuvant olaparib significantly extended invasive disease-free survival and overall survival, with benefit consistent across subgroups. The OlympiA approval study showed an iDFS benefit of 7.3% after four years and a benefit of 3.4% for overall survival.

Differentiation between these options is increasingly driven by nodal and biological eligibility criteria and comparative tolerability. MonarchE required ≥4 positive lymph nodes (LNs) or 1-3 LNs with tumor size ≥5 cm or grade 3 histology (Cohort 1), or 1-3 LNs with Ki-67 ≥20% (Cohort 2), whereas NATALEE included stage IIB-III and high-risk stage IIA (T2N0 with grade 3 or Ki-67 ≥20%). In a United States Electronic Health Records database analysis of 7060 patients with stage I-III HR+/HER2- EBC, 30.6% were eligible for NATALEE and 14.5% for monarchE, with 91.8% and 45.9% of N1 disease eligible for NATALEE and monarchE, respectively, and 9.5% of N0 disease eligible for NATALEE and none for monarchE. A matching-adjusted indirect comparison using individual patient data from NATALEE and aggregate data from monarchE cohort 1 showed similar invasive disease-free survival with weighted ribociclib + NSAI versus abemaciclib + ET (hazard ratio, 0.901; 95% CI: 0.678-1.197), with lower odds for diarrhea, leukopenia and lymphopenia and higher odds for increased alanine aminotransferase and neutropenia with ribociclib + NSAI versus abemaciclib + ET.