Extended intermittent letrozole not better than continuous use in SOLE study, but temporary treatment breaks may be safe for some patients

Intro text: 

-11 December 2017-

Results of the phase III SOLE study (Study of Letrozole Extension) presented at ASCO 2017 were published recently in The Lancet Oncology They show that extended intermittent letrozole treatment does not improve disease-free survival compared with the continuous use of letrozole, in postmenopausal women with hormone receptor-positive breast cancer. As reported by the study investigators, these findings also suggest an attractive treatment approach, since some patients could benefit from temporary treatment breaks without increasing the risks of cancer recurrence.


Study investigator Dr Marco Colleoni, Director, Division of Medical Senology at the European Institute of Oncology, Milan, Italy, member of the International Breast Cancer Study Group (IBCSG) and of the BIG Executive Board, says:

“These results did not support our main hypothesis, but they do support the safety of temporary treatment breaks, which would mean a lot for patients’ quality of life, and contribute to the further tailoring endocrine treatment.”

Study details

SOLE is the first trial evaluating a de-escalation of extended adjuvant endocrine therapy. From December 2007 to October 2012, it enrolled 4,851 postmenopausal women with hormone receptor-positive breast cancer who were cancer-free after surgery and had already completed 4 to 6 years of adjuvant endocrine therapy. 2,426 received extended continuous letrozole, and 2,425 patients intermittent letrozole that involved several treatment breaks. Scientists compared the disease-free survival rate (DFS, i.e. absence of cancer cells in the body) in the two groups after five years, and observed that DFS was 87.5% in the continuous letrozole group and 85.8% in the intermittent letrozole one.


22 countries involved

240 sites from 22 countries worldwide were involved in this trial, which was led by the International Breast Cancer Study Group (IBCSG) under the Breast International Group (BIG) umbrella and in collaboration with Novartis.