As these biomarkers may be non-invasively sampled in a prospective and serial manner, Mueller et al. demonstrated that mucus cystatin 2 and periostin levels were capable of predicting worsening SNOT-22 scores, a proxy for AE in CRSwNP, and even the need for revision surgery among patients with CRSwNP months in advance [24]. Here, CST2 is linked to chronic rhinosinusitis with nasal polyps.