Transformation of a benign oral pigmentation to primary oral melanoma

The objective is to report the serendipitous 7-year follow-up and transformation of a melanotic palatal lesion, which was initially diagnosed histologically as a benign oral melanotic macule, into primary oral melanoma and to provide long-term follow-up of a case of oral malignant melanoma.

Nine formalin-fixed paraffin-embedded tissue blocks from several different facilities and microscopic slides of the patient's lesions were reviewed to study the transformation of a benign, oral, pigmented lesion into melanoma.

Review of blocks and slides of the patient's lesions suggest that the onset of melanocytic hyperplasia (increased clear cell activity) heralded the transformation of the melanotic macule into melanoma. The histology of the first biopsies was totally benign, but retrospectively, the clinical appearance was not typical and was somewhat worrisome because of the size of the lesion and feathering of the pigmentation at the periphery. This clinical presentation, however, was unknown to the pathologists.

This study documents a case of primary oral melanoma arising from an apparent oral melanotic macule and suggests that even histologically benign-appearing oral melanotic lesions should perhaps be viewed with caution if increased numbers of melanocytes (melanocytic hyperplasia or clear cell activity) are present. Careful correlation of clinical appearance and histology is necessary to arrive at an appropriate diagnosis and prognosis for oral pigmented lesions.