Background and importance Nutritional support in breast cancer patients has an important role during oncological treatment, which varies according to the stage of the breast tumour. When surgery is performed followed by radiotherapy or chemotherapy, some of the possible adverse effects that may occur are caused by the interaction of this treatment with nutritional support.

Aim and objectives To investigate the possible drug–food interactions that can occur in breast cancer patients.

Material and methods We conducted a systematic review through searches in the databases PubMed, Scielo, MedlinePlus, Google Scholar and other sources, such as the National Cancer Institute and the World Health Organization, on possible food–drug interactions in patients with breast cancer. Inclusion criteria were works published in English or Spanish, from 2008 to 2019, and related to the treatment used in breast cancer. Key terms used were: breast cancer, drug–food interaction, treatment, nutritional support, chemotherapy and grapefruit juice.

Results 23 articles met the inclusion/exclusion criteria. Possible interactions were a consequence of decreased efficacy in treatment, increased toxicity of treatment, poor tolerance to nutritional support or nutritional deficiencies. Interactions could be physical, pharmacokinetic, pharmacodynamic or pharmacological. The probability that patients might experience adverse effects increased as drug plasma concentrations increased and by extrapolating the dynamic response. This situation has been evidenced for exemestane, a treatment in breast cancer whose absorption is influenced by food, particularly by grapefruit juice. It acts as a potent inhibitor of the intestinal activity of CYP3A4 and increases the bioavailability of various drugs. The identified substances in grapefruit juice that act as clinically important inhibitors of CYP3A4 are bergamotin and 6’,7’-dihydrobergamotin.

Conclusion and relevance There is a proven interaction between grapefruit juice and cancer treatment, particularly in breast cancer. Grapefruit juice contains bergamotin and 6’,7’-dihydrobergamotin, inhibitors of the CYP3A4 cytochrome P450 isoenzyme involved in the metabolism of various drugs. The inhibition increases plasma concentrations of several drugs, creating a risk of overdose and development of adverse effects. They also block other P450 isoenzymes and protein carriers, such as p-glycoprotein. Therefore, its consumption should be avoided during the treatment of breast cancer.

Conflict of interest No conflict of interest