NATALEE: Six-Year Follow-Up Moves the Discussion Toward Overall Survival

NATALEE (NCT03701334) is a global, randomized, open-label Phase III trial evaluating adjuvant ribociclib plus a non-steroidal aromatase inhibitor (NSAI) against NSAI alone in adults with HR+/HER2-negative early breast cancer at risk of recurrence. The trial enrolled 5,101 patients with stage IIA, IIB or III disease. Patients in the ribociclib arm received ribociclib 400 mg daily on a three-weeks-on, one-week-off schedule for three years, alongside letrozole or anastrozole for five years; premenopausal women and men also received goserelin when indicated. The primary endpoint was invasive disease-free survival (iDFS), while OS and other recurrence-related outcomes were secondary or exploratory endpoints. The six-year analysis assessed whether the benefits observed in earlier NATALEE readouts continued to deepen with longer follow-up.

Key Efficacy and Safety Highlights
Category	Parameter	Ribociclib + Endocrine Therapy (n=2549)	Endocrine Therapy Alone (n=2552)
Efficacy	Median OS follow-up	Six-year analysis; exact median follow-up not reported	Six-year analysis; exact median follow-up not reported
	OS hazard ratio	0.809	Reference
	Relative reduction in risk of death	19.1%	Reference
	Absolute OS benefit at 6 years	2.1 percentage points	Reference
	Breast cancer-specific survival HR	0.709	Reference
	Absolute BCSS benefit at 6 years	2.6 percentage points	Reference
	iDFS hazard ratio	0.741	Reference
	Absolute iDFS benefit at 6 years	5.3 percentage points	Reference
	DDFS hazard ratio	0.744	Reference
	Absolute DDFS benefit at 6 years	4.9 percentage points	Reference
	DRFS hazard ratio	0.738	Reference
	Absolute DRFS benefit at 6 years	4.4 percentage points	Reference
Safety	Secondary primary malignancies	3.0%	3.3%
Safety	Secondary primary malignancies leading to death	0.2%	0.2%
BCSS: breast cancer-specific survival; iDFS: invasive disease-free survival; DDFS: distant disease-free survival; DRFS: distant recurrence-free survival. The absolute benefits represent between-group differences at six years, not the percentage of patients surviving or remaining disease-free.

Conclusion

The six-year NATALEE results strengthen the evidence for adjuvant ribociclib plus endocrine therapy in HR+/HER2-negative early breast cancer at high risk of recurrence. The emerging OS benefit, alongside progressively greater iDFS and distant-recurrence benefits, suggests that treatment may deliver lasting clinical value beyond the three-year ribociclib course. The findings are particularly relevant because the trial included a broad high-risk population encompassing eligible node-negative and node-positive patients. While the OS results are clinically meaningful, continued follow-up will help clarify the magnitude and durability of the survival benefit. Overall, the data reinforce ribociclib’s role in adjuvant treatment discussions and highlight the growing importance of balancing recurrence risk, treatment duration and long-term outcomes when selecting therapy for early breast cancer.

Tags:

Executive Summary

The six-year NATALEE results strengthen the evidence for adjuvant ribociclib plus endocrine therapy in HR+/HER2-negative early breast cancer at high risk of recurrence.