In a clinical scenario of such heterogeneity and lack of other useful and available biomarkers for patients with uncontrolled moderate-to-severe asthma, the aims of this study were to (1) assess the stability over time of molecular T2 and non-T2 phenotypes, defined according to the simple biomarkers proposed by Woodruff (serum IgE levels and peripheral blood eosinophilia); (2) assess the correlation of these phenotypes with serum periostin levels; and (3) assess the correlation between serum periostin and asthma endotypes, on the path to personalized medicine in asthma. Here, POSTN is linked to asthma.