What is "recurrent nevus phenomenon"? if pathologist is not aware it is a recurrence why does it matter?

False DX of melanoma: When a benign or dysplastic nevus grows back after biopsy, and is re-biopsied or excised, it may now show features that closely mimic a melanoma under the microscope. This melanoma-like pattern is called "recurrent nevus phenomenon." A pathologist might accidentally misdiagnose a benign, recurrent nevus as melanoma, if they don't know (or don't suspect) it was previously biopsied.

Incompletely removed: A nevus is a benign skin growth (mole or beauty mark) that may be of concern if it has a changing or irregular appearance. A biopsy can be performed to determine if there are abnormal cells that would prompt removal. If not removed completely, it can recur. Further removal is then indicated if the cells were abnormal. It can be difficult to interpret pigmented cells, a challenge for pathologists.