Methasthysis is where the surgeon goes in and cuts a tumor to remove it, and tiny particles from it escape to the surrounding tissues carried by the lymph or bloodstream.
Like going into the forest and taking a big ole lichen of a tree, crumbling it up into a few chunks, and casting it into the forest while a little wind is blowing. Soon, you get lichen methasthesis in the forest, the lichens appearing on other organs (trees) of the forest where they weren't previously present.