Antimetabolites

A 38-year-old woman with metastatic colorectal cancer is being evaluated for 5-fluorouracil (5-FU) toxicity after developing severe hand–foot syndrome and mucositis. Which investigation would be most appropriate to identify patients at risk for severe 5-FU toxicity due to dihydropyrimidine dehydrogenase (DPD) deficiency?

Which feature best distinguishes 5-fluorouracil (5-FU) from methotrexate among antimetabolite chemotherapy agents?

A 48-year-old woman with metastatic colorectal cancer has completed 2 cycles of 5-fluorouracil (5-FU) and leucovorin. She now presents with severe hand-foot syndrome (palmar-plantar erythrodysesthesia), grade 3 diarrhea, and oral ulceration. Her performance status has declined. The oncologist is considering whether to continue, modify, or switch chemotherapy. What is the most appropriate immediate next step?

A 52-year-old woman with colorectal cancer is being treated with 5-fluorouracil. Her oncologist adds leucovorin to the regimen. Which feature best distinguishes the pharmacological effect of leucovorin addition from the mechanism of 5-FU itself?

Methotrexate exerts its cytotoxic effect by inhibiting which enzyme, leading to depletion of reduced folate cofactors required for nucleotide synthesis?