After presenting to the dermatologist for a full-body skin examination, a 48-year-old man was found to have a pale white patch on the right side of his back. The patch was completely asymptomatic, and he had never noticed it. The irregularly shaped patch had well-defined borders and was pale relative to the surrounding skin. The border between the patch and the surrounding skin was obliterated when a glass slide was pressed against the edge of the lesion.
What is your diagnosis?
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