A. Depending on how long it's been there, I'd consider a bee/insect sting reaction, penetrating foreign body, or benign or malignant tumor to all be possibilities. Your vet can do a procedure called a fine needle aspirate, in which a needle is used to remove some cells from the lesion to examine under a microscope, and hopefully obtain a diagnosis. If it persists surgical removal should be considered, as surgery on large ear flap masses can be tricky and may require removal of part of the ear.
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