Introduction: Oral anticancer therapy has the benefit of allowing cancer patients to carry out their treatment at home, without being inconvenienced or being at risk of nosocomial infection. However, non-adherence is a public health problem that contributes to the clinical decline of the patient and there are no studies submitted on the adherence of cancer patients to oral anti-anticancer agents in Santarém, PA.

Objective: In view of this, the general objective of this work was to evaluate this oral medication adherence.

Methods: The methodology consisted of a cross-sectional documentary study with a quantitative approach of patients seen at the pharmaceutical office. The Morisky–Green test was used to analyse the degree of adherence and descriptive and inferential statistics were used (p < 0.05).

Results: Patients’ adherence to antitumour therapy was not 100%, the majority belonging to females; men were the most adherent, showing adverse reactions to anti-anticancer agents (p = 0.0096); comorbidity (p = 0.0202) negatively impacted adherence.

Conclusion: It is necessary to adopt new clinical procedures that can contribute to the management of these variables that prevent adherence, in order to improve the effectiveness of the treatment of these patients. There are circumstances that go beyond the aspects inherent to the patient, so it is also relevant to research the external factors that influence the individual’s behaviour, such as the duration of therapy and the consequences of the treatment in the patient’s routine.