medwireNews: The final analysis of the SOLE trial has shown no significant difference in the outcomes of postmenopausal women with hormone receptor-positive breast cancer who received extended intermittent or continuous adjuvant letrozole.
As reported in the Annals of Oncology, the primary endpoint of disease-free survival (DFS) was achieved at the 7-year mark by a nearly identical 81.4% of patients in the intermittent letrozole group and 81.5% of those in the continuous group.
These results are in line with the previously reported 5-year rates, and confirm that the trial did not demonstrate the superiority of the intermittent regimen, say the study authors.
They highlight, however, that prior research has also shown “less worsening in symptom-specific and global quality of life” with intermittent versus continuous treatment, and taken together these findings “will be reassuring to patients and clinicians who may for various reasons need or choose to interrupt extended adjuvant therapy.”
The phase 3 study was initiated following preclinical work indicating that resistance to aromatase inhibitors such as letrozole “can be reversed” by intermittent use, explain the researchers, who recruited 4851 postmenopausal patients with node-positive disease who had already received 4–6 years of adjuvant endocrine therapy.
After a median 84 months of follow-up, all secondary endpoints were also comparable between participants who were randomly assigned to receive extended letrozole 2.5 mg/day for up to 5 years either on an intermittent (daily for 9 months followed by a 3-month break in years 1–4 and continuously in year 5) or continuous schedule.
For instance, at 7 years, 88.6% of patients in the intermittent group remained free from recurrence of invasive breast cancer, as did 88.0% of those in the continuous group, while the respective overall survival rates at this timepoint were 90.6% and 89.6%.
“SOLE was not designed as a non-inferiority study,” say Guy Jerusalem, from Liège University in Belgium, and co-investigators.
“Had it been so, the observed confidence intervals of the hazard ratio for DFS with intermittent therapy (0.91 – 1.17) would fit within the success parameters of most non-inferiority trials,” they conclude.
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