Study Of Letrozole Extension (SOLE) trial

17 November 2017


The SOLE trial aimed to find out if taking letrozole intermittently was better than taking it continuously.

Scientific Title

IBCSG 35-07/BIG 1-07. A phase III trial evaluating the role of continuous letrozole versus intermittent letrozole following 4 to 6 years of prior adjuvant endocrine therapy for postmenopausal women with hormone-receptor-positive, node-positive early-stage breast cancer


Previous research has indicated that breast cancers may be more sensitive to intermittent treatment with letrozole.


SOLE trial results showed that letrozole taken for 9 out of every 12 months, is as good as continuous letrozole in the extended treatment of early-stage breast cancer. No new side effects were noted, beyond what is already known about letrozole. Importantly, women who took intermittent letrozole reported that their quality of life was better, compared with those who took continuous letrozole. This may be because they were able to have time off letrozole, and the side effects were less during that break.

Now, because of this trial, women who have a sufficiently high chance of breast cancer recurrence to require 10 years of hormone-blocking therapy can safely have a break from that treatment for 3 months every year. This strategy may be particularly worthwhile for women who are experiencing troublesome side effects but want to remain on the medication to minimise their chance of breast cancer recurrence.

Main publication

Extended adjuvant intermittent letrozole versus continuous letrozole in postmenopausal women with breast cancer (SOLE): a multicentre, open-label, randomised, phase 3 trial. Marco Colleoni et al on behalf of the SOLE Investigators. Lancet Oncology. 17 November, 2017; S1470-2045(17)30715-5.