Many types of cancer remain largely incurable (such as pancreatic cancer) and the overall death rate from cancer has not decreased appreciably since the 1970s.
Thus, even proteins that have diverged appreciably in sequence but still share detectable similarity will also share common structural properties, particularly the overall fold.
Many commercial immunoassay screening tests directed at the amphetamines cross-react appreciably with pseudoephedrine, but chromatographic techniques can easily distinguish pseudoephedrine from other phenethylamine derivatives.