Breslow thickness of cutaneous malignant melanoma in paraffin wax and frozen sections

Breslow tumour thickness was measured in frozen and paraffin wax sections from 21 excision biopsies of cutaneous malignant melanomas by two observers. There was no consistent variation between frozen and paraffin wax sections, with recorded differences ranging from +0.3 mm to -0.2 mm. Interobserver differences ranged from +0.4 mm to -0.2 mm. The interobserver variations exceeded the intraobserver variations, but neither were significant. These findings show conclusively that, when using high quality frozen sections, there is no significant difference between Breslow thickness measured in frozen or paraffin wax sections and therefore that frozen sections can be used to microstage melanoma. Interobserver variations seem to be a more likely source of erroneous measurements of tumour thickness.