A 39-year-old female presents with chronic abdominal cramps, watery diarrhea, and periodic facial flushing. Physical examination reveals wheezing and a slightly enlarged liver. Workup reveals several masses within the liver and a large mass in the small intestine. Which one of the listed substances is most likely to be elevated in the urine of this individual as a result of her disease?
5-hydroxyindoleacetic acid (5-HIAA) Aminolevulinic acid (ALA) N-formiminoglutamate (FIGlu) Vanillylmandelic acid (VMA)