The plexiform spindle cell nevus nevi and atypical variants: report of 128 cases.

The plexiform spindle cell nevus (PLXSCN) is a distinct melanocytic lesion that often provokes concern for melanoma. We describe the features of 119 typical PLXSCNs and 9 atypical/high-grade lesions. Histologically, all cases had a fascicular plexiform architecture and were composed of predominately spindled cells. The 6 atypical plexiform spindle cell tumors (PLXSCTs) exhibited features such as greater mitotic activity, increased cellularity/nodular confluence, and more concerning cytological atypia. Three high-grade tumors (perhaps evolving plexiform spindle cell melanomas) had additional alarming clinical or histologic characteristics, such as patient age greater than 40 years, greater degree of cellularity, higher degree of cytological atypia, mitotic rate greater than 3/mm(2), regional lymph node metastases, and greater than 1 positive sentinel lymph node. Follow-up data were available for 18 typical PLXSCNs: all patients were without tumor recurrence or death in a mean follow-up period of 3.9 years (range, 1 month to 10 years). One atypical PLXSCT and 3 high-grade lesions had follow-up information: the atypical PLXSCT had sentinel lymph node involvement, and the patient was alive without recurrent disease at 1-year follow-up; 2 of the 3 high-grade lesions were positive for lymph node involvement, and all 3 patients were alive with 2-, 4-, and 0.8-year follow-up periods. All PLXSCTs should be completely excised with clear margins, and high-grade or potentially malignant lesions may require management as melanoma.