I had a seroma after my reconstruction and it took it several weeks to go away. It was painful and irritating. Seromas have nothing to do with cancer ok? :)
No, seromas are not life-threatening, just annoying or painful until they resolve on their own, or with additional measures by the doctor if they persist or are highly painful.
They will not bring back or contribute to the spread of cancer.
Best wishes,
bluebutterfly