Evaluation of Adherence to Cell Cycle Inhibitors Used as Adjuvant Therapy in Patients With Localized Breast Cancer at High Risk of Recurrence.

Hormone receptor-positive (HR+) breast cancers represent the most common histological subtype of breast cancer, accounting for approximately 75% of cases, regardless of HER2 (human epidermal growth factor receptor 2) status (1). Adjuvant endocrine therapy (ET), including tamoxifen and aromatase inhibitors (AIs), is an effective pharmacological treatment for improving the prognosis of HR+ breast cancer, reducing the risk of recurrence by up to 50% (2-3-4-6). Despite its proven prognostic benefit, the full potential of endocrine therapy is not realized due to patient non-adherence (i.e., failure to comply with prescribed treatment). Adjuvant endocrine therapy is generally prescribed for a duration of 5 to 10 years. However, up to 40% of patients discontinue treatment prematurely, and 30% take the medication less frequently than prescribed. Poor adherence and low treatment persistence carry a substantial mortality burden: non-adherence is associated with a 49% increase in all-cause mortality. A retrospective analysis of a large database including more than 8,700 patients showed a 10-year survival rate of 80.7% among women who continued treatment, compared with 73.6% among those who discontinued adjuvant therapy prematurely (p \< 0.001). Among patients who continued treatment, the survival rate was 82% in those who were fully adherent, versus 78% in those who were only partially adherent (7-16). The literature has documented a wide range of risk factors associated with non-adherence to or discontinuation of long-term adjuvant endocrine therapy. Treatment-related adverse effects, including hot flashes, joint stiffness, and sexual dysfunction, are common and may lead to treatment discontinuation. Fear of side effects may also prevent some patients from initiating or maintaining endocrine therapy. Others may not be fully convinced of the necessity of adjuvant endocrine therapy, particularly in the absence of overt signs of cancer. In addition, supportive care required to