metastasis (n.)

"change of substance, conversion of one substance into another," 1570s, originally in rhetoric, from Late Latin metastasis "transition," from Greek metastasis "a removing, removal; migration; a changing; change, revolution," from methistanai "to remove, change," from meta, here indicating "change" (see meta-) + histanai "to place, cause to stand," from PIE root *sta- "to stand, make or be firm." A rhetorical term in Late Latin for "a sudden transition in subjects," medical use for "shift of disease from one part of the body to another" dates from 1660s in English. Related: Metastatic.