Novel Additions to the AJCC's New Staging Systems for Skin Cancer

The eighth edition of the staging manual of the American Joint Committee on Cancer incorporates important changes in the classification of skin cancers. Coming 40 years after the first edition, the latest manual preserves its specific system for Merkel cell carcinoma and takes into account recent publications on the prognosis of squamous cell carcinoma by defining a completely new T category for this neoplasm. Staging for squamous cell carcinoma considers head and neck tumors (excluding the eyelid) and does not offer solutions for other sites except the vulva, penis, and perianal region. Regarding melanoma, use of the mitotic index has been eliminated and the prognosis of the primary tumor is based on Breslow thickness and ulceration. In addition, thickness is now recorded to an accuracy of 0.1mm, and the T0 concept has been introduced to define those metastatic melanomas in which the primary tumor has regressed completely. In this new edition, changes have also been made to the N category of all the skin cancer staging systems, and M1d has been added to the M category for melanoma to refer to metastatic involvement of the central nervous system, which, up to now, had been included in the M1c category. This new system will need to be validated with patient series to determine if it adequately satisfies the objective of tumor risk stratification.