Metastatic Breast Cancer Treatment Complicated by a Supplement–Drug Interaction

What happened, in summary

A 55-year-old woman with bilateral breast cancer and bone metastases was receiving ribociclib with letrozole for hormone-receptor-positive, HER2-negative disease. Treatment began in May 2019. When moderate neutropenia developed in 2020, the ribociclib dose was reduced, after which the blood-count problem became milder.

In July 2021, she began taking a dietary supplement containing diosmin, escin and resveratrol in an effort to reduce peripheral swelling. Two months later, moderate neutropenia returned. The supplement was stopped permanently, and ribociclib was temporarily suspended. After her blood counts recovered, ribociclib was restarted at the reduced dose together with letrozole.

The clinical team considered the supplement a possible contributor to the recurrent toxicity because its ingredients could interfere with the metabolism of ribociclib. Her case highlights the practical importance of discussing supplements during cancer treatment, especially when a patient is receiving medicines with known interaction risks. Her metastatic breast-cancer care continued after the toxicity was addressed.