Any skin lesion suspicious of melanoma should be completely excised with a 1 mm margin of normal surrounding skin and sent for detailed analysis by a histopathologist.
Guidelines differ, but a melanoma-in-situ and and invasive melanoma with a tumour thickness less than 1 mm should be excised with a 1 cm margin. Invasive melanoma greater than 1 mm in thickness should be excised with a 2 cm margin and certainly if the Breslow thickness is 2 mm or greater.
Data from: The United Kingdom Melanoma Study Group and the British Association of Plastic Surgeons (MSG/BAPS) multi-centre randomised trial of surgical width of excision margin in patients with thick cutaneous malignant melanoma.
| Breslow Thickness | Margin Size |
| < 1 mm | 1 cm |
| 1-2 mm | 2 cm |
| > 2 mm | 3 cm |