The following article features coverage from the 2017 American Society of Clinical Oncology (ASCO) Annual Meeting in Chicago, Illinois. Click here to read more of Cancer Therapy Advisor‘s conference coverage.

In postmenopausal women with hormone receptor–positive breast cancer, extended intermittent letrozole did not improve disease-free survival (DFS) compared with continuous letrozole therapy, though the rate of adverse events was similar in both groups, according to data from SOLE presented at the 2017 American Society of Clinical Oncology (ASCO) Annual Meeting in Chicago, Illinois.1

SOLE was a phase 3 study ( Identifier: NCT00553410) that tested whether 3-month treatment-free intervals during extended adjuvant therapy would improve DFS.

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Marco Colleoni, MD, of the European Institute of Oncology in Milan, Italy, presented on behalf of the SOLE investigators.

SOLE enrolled 4884 women with hormone receptor–positive, lymph-node positive breast cancer who had completed between 4 and 6 years of adjuvant endocrine therapy.  Patients were randomly assigned to an additional 5 years of continuous therapy with letrozole 2.5 mg daily (2441 patients) or to intermittent letrozole (2443 patients), which was administered for the first 9 months in years 1 to 4 and for 12 months in year 5.

At 60 months median follow up, 5-year DFS was 85.8% for the intermittent arm vs 87.5% for the continuous arm. With a hazard ratio of 1.08, there was no benefit in DFS for patients receiving intermittent letrozole.

Twenty-four percent of women discontinued letrozole early in both arms of the study.

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As the rate of adverse events in both groups was similar, “SOLE provides clinically relevant information for the intermittent use of letrozole and suggests that patients may benefit from temporary treatment breaks,” Dr Colleoni concluded.

Read more of Cancer Therapy Advisor‘s coverage of the 2017 American Society of Clinical Oncology (ASCO) Annual Meeting by visiting the conference page.


  1. Colleoni M, Luo W, Karlsson P, et al. SOLE (Study of letrozole extension): A phase II randomized clinical trial of continuous vs intermittent letrozole in postmenopausal women who have received 4-6 years of adjuvant endocrine therapy for lymph node-positive, early breast cancer. J Clin Oncol. 2017;35(suppl; abstr 503).