Introduction: Adjuvant treatment with aromatase inhibitors (AI) in oestrogen receptor-positive and/or progesterone receptor-positive breast cancer (BC) has been shown to increase overall survival. However, arthralgias and myalgias are common adverse effects in patients treated with AI.

Objective: To evaluate the frequency and characteristics of arthralgias and myalgias in patients with early BC-treated adjuvantly with AI in the Mastology Unit of the Oncology Service of the Hospital de Clínicas and the Departmental Hospital of Soriano.

Materials and methods: A prospective, cross-sectional and descriptive study was performed. A questionnaire was administered to patients to assess the presence and characteristics of arthralgias and myalgias associated with AI.

Statistical analysis: ‘Age’ was described with measures of central tendency and dispersion. Qualitative variables were presented in absolute and relative frequencies. Logistic models were used to evaluate the association between patient characteristics, tumour characteristics, treatment characteristics and the presence of pain. Results were presented by odds ratio and p-value, using R software (version 4.1.2) with a significance threshold of 5%.

Results: 83 patients were included, with a median age of 69 years. 75.9% presented arthralgias and/or myalgias related to treatment, with an average intensity of 5–7. 80.9% received non-steroidal anti-inflammatory drugs (NSAIDs), achieving satisfactory analgesia. The presence of arthralgias and myalgias was significantly associated with age and time since the last menstrual period (LMP), being more frequent in patients older than 50 years and those with more than 5 years since the LMP.

Conclusion: Approximately 70% of the patients presented arthralgias or myalgias. These findings suggest a possible role of oestrogen withdrawal in its mechanism of development. Multidisciplinary and translational research is crucial to evaluate the ethology and therapeutic options for patients with AI-related arthralgia.