レアケース

noun

rare case; outlier

A situation or instance that occurs infrequently; often used in medical, statistical, or everyday contexts to describe something unusual.

• この病びょう気きはレアケースで、医い者しゃもあまり見みたことがない。

  This illness is a rare case; even doctors haven't seen it much.

• 統とう計けい的てきに見みれば、それはレアケースだ。

  Statistically speaking, that's an outlier.