JoEllen Zembruski-Ruple, 65, began chemotherapy for squamous cell carcinoma at Memorial Sloan Kettering Cancer Center on January 29, unaware of the risks associated with the drug capecitabine, which she was deficient in metabolizing. After experiencing severe side effects, including oral infections and gastrointestinal distress, she was admitted to hospice care and died on March 25 from the drug’s toxic effects, highlighting the need for genetic testing to prevent such fatalities. Despite recent FDA warnings and evolving guidelines, testing for enzyme deficiencies remains inconsistent, prompting calls for routine screenings before chemotherapy treatment.