There is not much difference between a lesion and a tumor. That is a reason wh7y these terms are often used interchangeably.
A difference, if there is one, is that a lesion is something that can be a tumor, a pocket of infection like an abscess
, or a skin abnormality like a papule. A tumor is a swelling or mass and is used to describe a benign or malignant neoplasm or growth.