Significant risk of relapse remains for ER-positive breast cancer patients beyond 10 years

Recent studies have shown that 10 years of adjuvant tamoxifen further improves breast cancer survival compared with 5 years of adjuvant therapy, albeit at a cost of 0.4% due to mortality resulting from endometrial carcinoma or pulmonary embolism. The studies underline the critical importance of sufficiently large patient populations and longer follow-up to provide accurate outcome data.

The report by Colleoni et al. describes clinical trial results from a median 24-year follow up. Patients with ER-positive disease require long-term follow up, which should be fundamentally different from those with ER-negative and/or human epidermal growth factor receptor 2–positive disease, who require shorter follow-up. Given these differences, adjuvant clinical studies with shorter follow-up periods will underreport events for ER-positive patients.

The study also reports a secondary malignancy rate of 4.9%, a figure likely to be underreported in studies with shorter follow-up schedules.

Limitations of the study arise from the time period in which it began. Regimens used in the study (different schedules of cyclophosphamide, methotrexate, and fluorouracil, and 1 year of tamoxifen with or without prednisone) have been shown to be inferior to newer regimens. None of the patients received postoperative radiotherapy, in accordance with data available at the time. Today, women with node-positive disease receive locoregional radiotherapy to reduce the risk of locoregional recurrence.

Studies with long-term follow up periods offer insights into both efficacy and safety; however, such studies require extensive resources. The entities that decide which types of cancer care are made available, such as insurance companies, governments, and regional health care funders, must shoulder the responsibility to ensure the required long-term evaluation of these treatments is conducted. Joint projects between pharmaceutical companies and health care providers could identify long-term benefits and adverse effects. The process may be more readily implemented in countries with population-based cancer registries.

Dr. Jonas Bergh is professor in the department of oncology-pathology at Karolinska Institutet and University Hospital, Stockholm. Dr. Kathleen Pritchard is a medical oncologist at Sunnybrook Odette Cancer Centre and professor at the University of Toronto. Dr. David Cameron is clinical director and chair of oncology at the University of Edinburgh Cancer Research Centre, Scotland. These remarks were part of an editorial accompanying the report by Colleoni et al. (J Clin Oncol. 2016 Jan 18. doi: 10.1200/JCO.2015.65.2255). Dr. Bergh reported financial ties to Amgen, AstraZeneca, Bayer HealthCare Pharmaceuticals, Merck, Pfizer, Roche, and Sanofi. Dr. Pritchard reported ties to AstraZeneca, Pfizer, Roche, Amgen, Novartis, GlaxoSmithKline, and Eisai. Dr. Cameron reported ties to Novartis.