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

 Luca Roncati, Francesco Piscioli

Abstract:

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.