FIGURE 4.

Serum KL‐6 and CYFRA 21‐1 are associated with the presence and extent of systemic sclerosis‐associated interstitial lung disease (SSc‐ILD). KL‐6 is a mucin‐like glycoprotein (MUC1) that is expressed by type II pneumocytes, and CYFRA 21‐1 is expressed by alveolar and bronchiolar epithelial cells. Serum KL‐6 and CYFRA 21‐1 levels were measured in a retrospective (n = 189) and a prospective (n = 118) cohort of SSc‐ILD patients. Serum KL‐6 and CYFRA 21‐1 correlated with the presence and severity of ILD, with higher levels in SSc‐ILD compared to SSc‐no ILD, and in extensive compared to limited ILD. Serum KL‐6 levels in no‐ILD, limited ILD and extensive ILD in the (A) retrospective and (B) prospective cohorts. Serum CYFRA 21‐1 levels in no‐ILD, limited ILD and extensive ILD in the (C) retrospective and (D) prospective cohorts. Central lines indicate median values with boxes showing the 25th and 75th percentiles, whiskers indicate upper and lower quartile + 1.5 × interquartile range. Reproduced from Stock et al., ⁵³ with permission