[The importance of adherence to oral therapies in the field of oncology: the example of breast cancer].

Today, over 40 different oral anticancer therapies are available in the French prescription pricing authority dictionary. Adherence to these therapies has become a major issue in the field of oncology. Most of the available research has focused on adherence to hormonal therapy for breast cancer (BC). The objective of this paper is to synthesize current knowledge on adherence and persistence to hormonal therapy for BC. Available studies display significant heterogeneity due to variability in the measurements and data sources used, as well as in the timing of the measurements. Adherence and persistence estimates have recently been summarized in a meta-regression analysis. For tamoxifen, adherence ranges from 79% at one year to 65% at five years, and for Aromatase Inhibitors (AI), from 80% at one year to 72% at five years. Persistence decreases with the increasing duration of treatment: from a high of 86% of patients persistent at 1 year to a low of 53% at five years for tamoxifen, and from 88% to 69% for AI. Some of the modifiable determinants of adherence are directly linked to the patient-physician relation, to information provided during consultations, or to the specialty of the physician involved in the patient follow-up. Non-modifiable determinants, such as age or comorbidities, can be used to identify sub-groups of patients at high risk of non-adherence in order to target interventions. Few trials have been conducted in oncology to evaluate the efficacy of interventions to improve adherence. Adherence directly impacts both the efficacy of treatment and long-term treatment costs. Interventions to improve adherence to oral therapies should be systematically promoted in oncology. Improving adherence should be considered a priority in the field, lest physicians continue writing inefficient prescriptions for highly efficacious treatments.