Systemic sclerosis: To subset or not to subset, that is the question.

Systemic sclerosis (SSc) is a heterogeneous disease with variability in autoantibody profiles, skin and internal organ involvement, disease trajectory, and survival. The ability to identify more homogeneous subsets of SSc patients has informed patient care and been an essential aspect of SSc research. In this article, the historic evolution of subsetting systems in SSc are described including clinically based SSc subsetting systems, their utility, strengths, and limitations. There is a shifting paradigm of SSc subsets, including biologic classification of SSc subsets and fully data-driven approaches to SSc subset classification, taking into consideration the needs of the SSc global community in the modern era and the ability to prognosticate patients with SSc.