Predictive Biomarkers and Novel Treatments for the Progressive Fibrosing Phenotype in Interstitial Lung Disease Associated with Connective Tissue Disease.

Progressive fibrosing interstitial lung disease (PF-ILD) is a significant complication of connective tissue diseases (CTDs), particularly in systemic sclerosis (SSc), rheumatoid arthritis (RA), and idiopathic inflammatory myopathies (IIM). Despite clinical similarities with idiopathic pulmonary fibrosis (IPF), CTD-associated ILDs exhibit distinct pathogenetic and immunologic features. This review aims to summarize key predictive biomarkers and current treatment strategies associated with the progressive fibrosing phenotype in SSc-ILD, RA-ILD, and IIM-ILD. We conducted a focused literature search of PubMed and Scopus databases covering publications from January 2010 to February 2024. Included studies evaluated serum, cellular, or genetic biomarkers with predictive value for disease progression or treatment response. Only peer-reviewed English-language articles were included. Exclusion criteria encompassed single case reports and editorials. Several biomarkers, including KL-6, SP-D, CXCL4, and anti-MDA5, demonstrate potential in predicting fibrotic progression in CTD-ILDs. However, variability in sensitivity and specificity across CTD subtypes limits broad clinical applicability. Therapeutic agents such as nintedanib and pirfenidone show efficacy in slowing lung function decline. Biologics including rituximab and tocilizumab offer additional options, particularly in immunologically active diseases. Although promising biomarkers and therapies are emerging, no single marker or intervention currently predicts or modifies PF-ILD outcomes across all CTD subsets. Prospective studies and integrative biomarker panels are needed to improve patient stratification and guide therapy.