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 mitotic count in a or b T1 categorization for melanoma, but it adopts a sub-stratification based on Breslow's depth. Today, the death burden of thin melanoma is still severe, despite attempts for early screening. We believe that bio-histological implementation can explain this evidence. It is generally accepted that melanoma progression includes two subsequent phases: radial growth phases (RGP) and 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 capacity. Our experience shows that thin melanoma has three bio-histological subtypes: non-tumorigenic micro-invasive RGP without significant regression; micro-invasive RGP with regression of uncertain tumorigenic potential at diagnosis due to the extensive presence (>75%) of regression which can contain a VGP clone and micro-invasive tumorigenic VGP. Therefore, we support the conclusion that the diagnosis in melanoma is correlated with the type of growth phase inside it.