Prognostic index for cutaneous melanoma: an analysis after follow-up of 2715 patients

In 2715 of 4524 patients with cutaneous melanoma treated surgically between 1968 and 1992 prognostic parameters were analysed for their value in predicting the occurrence of first progression. All of the 2715 patients developed only one invasive cutaneous melanoma during the follow-up period. Data concerning tumour thickness and mitotic index (maximum number of mitoses per square millimetre) of the cutaneous melanomas were determined. Between the characteristics age, tumour thickness, mitotic index, prognostic index (PI), sex, site of tumour, melanoma subtype and Clark level, the value of the mitotic index, as a prognostic parameter independent of tumour thickness, and the combination of mitotic index and tumour thickness were evaluated. The development of the first metastases was documented during a mean follow-up of 7.5 years. The majority of first recurrences occurred at regional lymph nodes and attempts have been made to identify those patients at risk of developing metastatic disease. The most effective parameters proved to be tumour thickness and mitotic index. For both parameters an independent prognostic influence was shown. The prognostic index, defined as the product of tumour thickness and number of mitoses per square millimetre, was re-evaluated and confirmed. A new modified prognostic index, defined as the product of square tumour thickness and mitotic index, proved to be even more useful for defining a subgroup of patients who are at risk of developing metastases and, therefore, might benefit from adjuvant therapy.