C-reactive protein as an early marker of immune-related adverse events

Purpose Immune checkpoint inhibitors (ICIs) are effective against a wide variety of cancers. However, they also induce a plethora of unique immune-related adverse events (irAEs). Since for many organ systems symptoms can be unspecific, differential diagnosis with progression of disease or infection may be difficult. C-reactive protein (CRP) has been suggested as a marker for infection. The purpose of this study was to evaluate the diagnostic value of CRP in differentiating infectious causes from autoimmune side effects induced by ICIs. Methods In order to investigate the role of CRP in irAEs, we screened our patient data base. Only events with full infectious workup were included. In total 88 events of irAEs in 37 melanoma patients were analyzed. CRP levels before and during irAEs were evaluated. Statistical analyses were conducted using the Chi-square test for categorical variables. Results At the onset of irAE, CRP rose in 93% of cases to a mean of 52.7 mg/L (CI 35.1-70.3) from 8.4 mg/L at baseline (normal < 5 mg/L) (P < 0.0001). Other causes of CRP elevation including infectious diseases were excluded, and procalcitonin (PCT) levels were normal in 92% of events. Importantly, in 42% of cases CRP elevations preceded clinical symptoms. Conclusion CRP elevation can predict the onset of irAEs in patients treated with ICIs in the absence of infectious disease.