AJCC 8th Edition (2017) versus AJCC 7th Edition (2010) in thin melanoma staging.

In comparison with the 7th Edition, the 8th Edition of the American Joint Committee on Cancer (AJCC) staging system no longer considers the mitotic count in the a or b T1 categorization for melanoma, but it adopts a sub-stratification based on the Breslow's depth. Today, the death burden of thin melanoma is still severe, despite of attempts for early screening. We believe that a bio-histological implementation may explain this evidence. It is generally accepted that melanoma progression includes two subsequent phases: the radial growth phases (RGP) and the vertical growth phase (VGP). If left untreated, RGP is able to move towards VGP. In this second phase, melanoma grows as a malignant, mitotically active, tumor with invasive and metastatic capacities. By our experience, thin melanoma includes three bio-histological subtypes: the non-tumorigenic micro-invasive RGP without significant regression, the micro-invasive RGP with regression of uncertain tumorigenic potential at diagnosis, due to the extensive presence (> 75%) of regression which could contain a VGP clone, and the micro-invasive tumorigenic VGP. Therefore, we are prone to support that the prognosis of thin melanoma is correlated with the type of growth phase inside it.