Critical Review-A Tribute to Louis Brocq Lymphomatoid Papulosis, the Key in Exploring the Relationship of Parapsoriasis and Mycosis Fungoides.

Both parapsoriasis and LyP appear clinically as inflammatory dermatoses with a paradoxical link to cMF. A key element in addressing the relationship of parapsoriasis and MF were the results of the French and Dutch long-term registries tracking the emergence of lymphomas in the setting of LyP. Both cMF and cALCL emerged almost equally in these long-term studies. This ultimately supports that the stem cells in both cMF and cALCL are probably derived from a common stem cell shared by CD4+/CD8+ memory stem cells defining cMF and CD30+ stem cells defining cALCL. The discovery of inducible Skin Associated Lymphoid Tissue (iSALT) mesenchymal hubs incorporating Tregs, with their pleiotropic functions represents a paradigm shift and formed a translational tool in this analysis of the paradox. LyP can be recast as activated inhibitory lymphomatoid T-cell hubs derived from inducible iTregs in iSALT and the source of the common stem cell LyP line. iSALT Treg integrated mesenchymal hubs provided an emerging translational tool in redefining integrated lymphomatoid pathways. Brocq's complex scheme defining parapsoriasis as hybrid inflammatory dermatoses with a paradoxical link to cMF became a template to preserve parapsoriasis as a clinical diagnosis. Two major iSALT Treg generated inhibitory integrated lymphomatoid hubs emerged. The major CD30+TNF lymphomatoid hub has been linked to cALCL. Clinically defined chronic regressing and relapsing parapsoriasis with the histopathology of patch stage MF can be redefined as lymphomatoid parapsoriasis. This twin inhibited oncogenic memory based hub is defined by Treg modulated, CD4+/CD8+memory linked PD-1/DL-1 cytoxic complex and lichenoid histopathology.