A white, opalescent lesion of the buccal mucosa disappears or fades significantly when the mucosa is stretched. What is the most likely diagnosis?

The key diagnostic feature of leukoedema is that the white, opalescent appearance fades or disappears when the buccal mucosa is stretched, and reappears when the stretching is released. This transient nature distinguishes it from leukoplakia (which does not change with stretching) and white sponge nevus (a hereditary condition that persists when stretched). Leukoedema is a benign, bilateral, diffuse opacification of the buccal mucosa with no malignant potential. It is more prevalent in darker-skinned individuals and in smokers. No treatment is required; biopsy should be performed only if there is diagnostic uncertainty.