Melanoma in situ and low risk pT1a melanoma: Need for new diagnostic terminology.

Melanoma incidence has risen rapidly, at least until recently, while mortality has changed only a little, a phenomenon suggestive of overdiagnosis, which can be defined as the diagnosis as "melanoma" of a lesion that would not have had the competence to cause death or symptoms even if it had not been excised. Overdiagnosis has been attributed to efforts at early diagnosis ("overdetection"), and to changes in criteria resulting in diagnosis as melanoma of lesions previously termed nevi ("overdefinition"). In terms of overdefinition, there is evidence that criteria for the histopathologic diagnosis of melanoma has changed over a period of approximately two decades. Specialization may play a role in overdefinition; research has shown that when pathologists interpret the same lesion, dermatopathologists are more likely to diagnose low stage (AJCC T1a) melanomas and general/surgical pathologists are more likely to diagnose atypical nevi. An important subset that contributes to overdiagnosis is those melanomas that lack the property of tumorigenic vertical growth phase, thus lacking metastatic competence, and perhaps not warranting diagnosis as overt melanomas. Studies have defined subsets of patients with very low stage lesions diagnosed as melanomas in which observed survival has been 100%. In the past, many of these lesions would have been diagnosed as nevi, constituting overdefinition. Other key characteristics for very low risk (or no risk) lesions that are currently termed invasive "melanomas" include low Breslow thickness, Clark's level II invasion, absence of mitoses, and clinically, lack of observed or experienced dynamic changes. We propose a provisional terminology for diagnosing extremely low risk subgroups as "Melanocytic neoplasms of low malignant potential", aimed at reducing the negative personal and social effects of a cancer diagnosis for patients whose health and wellbeing are in reality not affected by an overdiagnosed "melanoma". With additional confirmation and appropriate consensus, it is likely that some of these subgroups can be reclassified as atypical or dysplastic nevi.