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. 2015 Mar;185(3):704–716. doi: 10.1016/j.ajpath.2014.11.021

Figure 6.

Figure 6

Proposed role of protein S6 kinase, 90 kDa, polypeptide 1 (RSK1) activation in a parallel progression model of melanoma. Schematic depicting the linear progression model of melanoma and the parallel progression model that we propose. Linear progression model: Superficial spreading melanoma (SSM) and nodular melanoma (NM) grow according to a linear model of progression, as malignant or normal melanocytes spread radially and then invade vertically. Parallel progression model: SSM and NM develop along divergent pathways from the transformed melanocyte to the primary melanoma, and these differences are maintained as the tumors invade and metastasize. p-RSK1, phospho-RSK1; RGP, radial growth phase; VGP, vertical growth phase.