Alternative serum biomarkers emerged during the last decades, such as inhibitory cytokine-1 (MIC-1), CEACAM1, osteopontin (OPN), MUC-1, HSP70 and ULBP2 [7–12], and panels of other emerging serum markers, capable of discriminating PC patients from healthy subjects, have been also reported [7]. Here, SPP1 is linked to pachyonychia congenita.