Problems in assessing multiple cutaneous melanoma. A review on the accuracy of a population based cancer registry.

Databases with information on malignant tumors are of great value for epidemiologic studies. From the Regional South Swedish Tumour Registry, which is of documented high quality, 24 patients out of 8008 with reported melanoma diagnosis 1973-2003 were reported as having multiple (> or =3) primary, invasive cutaneous malignant melanomas (CMM). Of the 76 tumours identified in these patients, 7 (9%) were found not to be invasive melanomas. Additional cases could be put into question since the lesions could be interpreted as epidermotropic metastases, a diagnosis which can be difficult to establish reliably by microscopic examination. Among the 24 patients we could also identify 8 (10%) additional lesions representing invasive CMM, not included in the Tumour Registry database. Thorough information concerning an earlier melanoma diagnosis and its site of presentation is needed from the clinician and the pathologist for optimal assessment of the histology and the prognostication of the patient, as well as proper reporting to a tumour registry. Identifying multiple primary malignant melanomas is also of special importance for counselling patients belonging to families with hereditary disease. In this study it is shown that diagnosing and reporting multiple malignant melanomas can be problematic due to insufficient communication and to the rare and deceptive capability of cutaneous metastases to imitate primary tumours.