Wow, it's not every day I hear about 5FU! It's an incredibly potent anti-cancer drug and one of its quirks is the active dose is very close to the fatal dose,

Wow, it's not every day I hear about 5FU! It's an incredibly potent anti-cancer drug and one of its quirks is the active dose is very close to the fatal dose, and there is high variability amongst individuals wrt dosage. It (probably) works by inhibiting a protein that makes the T DNA residue from making more T, which is fatal to rapidly growing cells.