p53-protein and Ki-67-antigen expression are both reliable biomarkers of prognosis in thick stage I nodular melanomas of the skin.

The maximum tumour thickness is the most important prognostic factor in malignant melanomas of the skin. However, the clinical outcome of thick nodular melanomas remains unpredictable. Therefore, we investigated possible prognostic markers in this subset of melanomas. From a melanoma data base, 12 patients with thick (> 3 mm) stage I nodular melanomas of the skin were identified, who were still without signs of progression after five years of follow-up. These tumours were compared to randomly selected series of 12 cases, who did not survive the first five years after removal of the tumours. We performed immunostaining for the p53-protein and the proliferation associated Ki-67-antigen. For quantification of immunostaining the tumours were entirely scanned. In addition, all tumours were investigated for any differences with conventionally applied prognostic features: the tumour thickness: the level of invasion; the prognostic index (tumour thickness multiplied by mitotic count); and the mean volume-weighted mean nuclear volume. We demonstrated significant differences between survivors and non-survivors exclusively in respect of the staining indices for p53 and Ki-67 (P < 0.03 and 0.02, respectively). With both antibodies the tumours of survivors showed lower counts as compared to non-survivors survivors. However, within both groups we found no significant correlations between the p53- and Ki-67-staining results. We conclude that immunostaining for p53-protein and Ki-67-antigen is helpful to identify individuals with thick nodular melanomas who are at risk of metastatic disease.