Ferritin as a diagnostic, differential diagnostic, and prognostic marker for immune-related adverse events

Introduction

Immune checkpoint inhibitors (ICIs) targeting cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4) or programmed cell death 1 receptor (PD-1)/programmedcell death 1 ligand 1 (PD-L1) pathways are influencing new cancer treatment model sand producing unprecedented clinical effects in a wide diversity of cancers, such as melanoma, renal cell carcinoma, lung cancer, urothelial cancer, or head and neck cancer^1–6. However, these treatments induce a series of distinct immune-related adverse events (irAEs), which are similar to autoimmune responses. Virtually every organ of the body is affected by irAEs, such as pneumonitis, colitis, endocrinopathies, and hepatitis; rarer adverse effects include myocarditis and neurotoxicity^7,8. The gastrointestinal, pulmonary, dermatologic, hepatic, and endocrine systems are thereby frequently affected. The ASCO Clinical Practice Guideline Summary provides system-based toxicity diagnosis and management guidelines, which recommend treatments depending on the affected system. The major treatment for ICI-related AEs is immunosuppression with methylprednisolone⁸. Because of the adverse effects of steroid-refractory, immunosuppressive effects are in facilitating escalation, including other immunosuppressants like tocilizumab, mycophenolate mofetil, or infliximab⁸. Although these irAE symptoms are usually reversible and controllable, they often lead to treatment disruption or dose reduction, and/or discontinuation of checkpoint treatment. When new symptoms appear during ICI treatment, other etiological factors such as infections, viral reactivation, tumor progression, or toxicity associated with other drugs must be excluded. Because a host of organ system symptoms are unspecific in irAE, diagnosis and differential diagnosis have become difficult. Especially with a combination of immunotherapy with chemotherapy or targeted therapy, distinguishing irAEs from AEs caused by chemotherapy or targeted therapy is very difficult. The diagnosis and differential diagnosis of irAEs play a major role in the treatment of AE and in subsequent tumor treatment decisions.

Recently, Abolhassani et al.⁸ have evaluated the value of CRP in diagnosing irAEs through retrospective analysis of the correlations among 88 events of irAEs in 37 patients with melanoma and their serumc-reactive protein (CRP) levels. Elevated CRP was predictive of irAEs in patients without infectious disease who were treated with ICIs. Liudahl and colleagues⁹ have reported a relationship between enhanced risk of high-grade irAEs in patients treated with ICIs and inchoate therapy-induced changes in circulating B cells. Bamias¹⁰ has shown that levels of CRP pre-therapy, combined with IFN-γ and IL-17, may be used to predict irAE development. These study designs were retrospective; therefore, a control group without AEs or with non-irAEs was not included. ICIs combined with chemotherapy or other therapies are increasingly and widely used in tumor treatment, and distinguishing irAEs from the AEs caused by chemotherapy or other treatments will be difficult. Thus, markers for convenient and rapid detection and differentiation of irAEs from infections or other AEs are urgently needed. At present, no effective marker can distinguish irAEs from infections or other AEs. Serum ferritin, a marker of inflammation, infection, and malignancy, continues to be measured in patients with cancer. On October 28, 2018, a patient with adrenal carcinoma and PD-L1 > 50% in tumor tissues received PD-1 inhibitor treatment in our department. After 1 day of treatment, the patient had panic symptoms. Electrocardiography indicated bigeminy with premature ventricular contraction. Myocardial enzyme indexes were abnormally elevated. Serum ferritin increased from 67 µg/L at baseline (normal range, 35–150 µg/L) to 7,680 µg/L. After 3 days, the patient developed heart failure, renal failure, and respiratory failure. The patient was diagnosed with the grade 4 irAE of explosive autoimmune myocarditis and received high-dose methylprednisolone, mycophenolate mofetil, high-dose immunoglobulin, and plasma exchange to treat the irAE. After 30 days of treatment, the patient recovered from the irAE. During the 30 days of treatment for the irAE, ferritin and myocardial enzymes simultaneously decreased to normal levels. Therefore, we wondered whether ferritin might serve as a diagnostic and prognostic indicator of irAE. Consequently, we designed this study to evaluate the diagnostic, differential diagnostic, and prognostic value of ferritin in irAEs induced by ICIs.

Materials and methods

Results

Diagnosis

At the onset of 90 irAEs, the ferritin (normal range, 35–150 µg/L) rose to a median of 927 µg/L (range, 117–17,825 µg/L) from 86 µg/L at baseline (range, 29–421 µg/L) (P < 0.001). The ferritin at AE onset in 20 grade 1 irAEs (median, 272 µg/L; range, 117–423 µg/L) was significantly higher than that at baseline in 90 irAEs (P < 0.001). The ferritin at AE onset in 41 grade 2 irAEs (median, 856 µg/L; range, 231–1,879 µg/L) was significantly higher than that in grade 1 irAEs (P < 0.001). In addition, we compared 23 grade 3 irAEs (median, 3,054 µg/L; range, 1,456–7,078 µg/L) with grade 2 irAEs (P < 0.001), and compared 6 grade 4 irAEs (median, 7,260 µg/L; range, 6,754–17,825 µg/L) with grade 3 irAEs (P < 0.001) (Figure 1A). In grade 1 irAEs, the ferritin levels at AE onset were significantly higher than those at baseline (median, 93 µg/L; range, 32–192 µg/L) (P < 0.001) (Figure 1B), and in grade 2 irAEs (Figure 1C), grade 3 irAEs (Figure 1D), and grade 4 irAEs (Figure 1E).

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Figure 1

Ferritin values at baseline and AE onset in the irAE group. The bars represent the median and range. (A) Ferritin values at baseline and AE onset for 90 irAEs; ferritin at AE onset for 20 grade 1 irAEs, 41 grade 2 irAEs, 23 grade 3 irAEs, and 6 grade 4 irAEs; (B) ferritin for 20 grade 1 irAEs; (C) ferritin for 41 grade 2 irAEs; (D) ferritin for 23 grade 3 irAEs; (E) ferritin for 6 grade 4 irAEs. ***, P < 0.001.

Differential diagnosis

The ferritin levels at AE onset in the irAE group were significantly higher than those in the non-irAE group (median, 81 µg/L; range, 32–478 µg/L) (P < 0.001) and the AE group (median, 103 µg/L; range, 23–712 µg/L) (P < 0.001) (Figure 2A). The ferritin at AE onset in 16 patients with pneumonia in the irAE group (median, 1,765 µg/L; range, 635–8,134 µg/L) was significantly higher than that of 27 patients with pneumonia in the non-irAE group and AE group (median, 134 µg/L; range, 27–478 µg/L) (P < 0.001) (Figure 2B). In addition, we observed 18 hepatitis cases in the irAE group (median, 3,008 µg/L; range, 902–17,825 µg/L), compared with 23 in the non-irAE group and AE group (median, 86 µg/L; range, 32–298 µg/L) (P < 0.001) (Figure 2C); 14 rash cases in the irAE group (median, 517 µg/L; range, 201–17,825 µg/L) compared with 13 in the non-irAE group and AE group (median, 71 µg/L; range, 33–151 µg/L) (P < 0.001) (Figure 2D); and 13 fever cases in the irAE group (median, 487 µg/L; range, 187–2,899 µg/L) compared with 6 in the non-irAE group and AE group (median, 131 µg/L; range, 63–267 µg/L) (P = 0.002) (Figure 2E).

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Figure 2

Ferritin values at baseline and after AE onset among groups. The bars represent the median and range. (A) Ferritin at AE onset in the irAE group; ferritin at baseline and AE onset in the non-irAE group and the AE group; and baseline ferritin in the no irAE-nonir AE group and no AE group; (B) ferritin at AE onset for pneumonia; (C) ferritin at AE onset for hepatitis; (D) ferritin at AE onset for rash; (E) ferritin at AE onset for fever. ***, P < 0.001.

Prognosis

After treatment in the irAE group, the ferritin continuously decreased to a normal range in 62 effective patients (endpoint median, 75 µg/L; range, 34–95 µg/L); no significant changes in ferritin were observed in 4 stable patients (endpoint median, 2,317 µg/L; range, 678–4,770 µg/L); and the ferritin continued to rise in 4 patients who died (endpoint median, 16,954 µg/L; range, 11,217–17,825 µg/L) (Figure 3).

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Figure 3

Changes in ferritin levels after treatment in 62 recovered patients, 6 stable patients, and 4 patients who died.

Discussion

In this study, patients who received ICI therapy, chemotherapy, or ICI therapy plus chemotherapy were included. We analyzed the ferritin levels in patients with irAEs, non-irAEs, AEs caused by chemotherapy, or no AEs to better evaluate the diagnostic, differential diagnostic, and prognostic value of ferritin for irAEs induced by ICIs. The median ferritin at AE onset was significantly higher than the baseline ferritin in patients with irAEs. The median ferritin at AE onset increased with irAE grade, and statistically significant differences were observed among grades. The median ferritin at AE onset for each grade was significantly higher than the baseline ferritin for the corresponding irAE grade. Therefore, ferritin can serve as a predictive and diagnostic marker of irAEs. The median ferritin level at AE onset in patients with irAEs was significantly higher than that in patients with non-irAEs or AEs caused by chemotherapy. The ferritin level at AE onset for the irAEs pneumonia, hepatitis, rash, or fever were significantly higher than those for non-irAEs or AEs caused by chemotherapy. These results showed that the ferritin can serve as a differential diagnostic marker to distinguish irAEs from non-irAEs. After treatment in the irAE group, the ferritin continuously decreased to normal ranges in effective patients, showed no significant changes in stable patients, and continued to rise in patients who died. The change in ferritin levels reflects the therapeutic effects of ICIs on irAEs, thus indicating that ferritin is a prognostic biomarker of irAEs.

The French scientist Laufberger discovered ferritin in 1937¹¹. In 1972, Addison et al.¹² used immunoradiometric assays and validated the ability to detect ferritin in human serum. In addition, ferritin is secreted by Kupffer cells, hepatocytes, and macrophages¹³. Although numerous facets of the basic biology of serum ferritin remain unclear, various effects are increasingly being ascribed to extracellular ferritin, including newly discovered effects such as angiogenesis, immunity, cancer, inflammation, iron delivery, and signaling¹⁴. According to early in vitro studies, ferritin regulates the body’s immune function by inhibiting the function of lymphocytes¹⁵. Lymphocytes are activated by phytohemagglutinin and concanavalin A when human lymphocytes are treated with spleen ferritin¹⁶. Subsequently, another in vivo study has shown that ferritin suppresses immunity. Excess iron restrains the function of helper T (CD4) cells, as well as the tumoricidal action of monocytes and macrophages, and influences the distribution of the T-lymphocyte subset^17,18. In patients with hereditary hemochromatosis, iron overload decreases the numbers and activity of CD4 cells, and increases the numbers and activity of suppressor T (CD8) cells, thus increasing the CD8:CD4 ratios¹⁹. Therefore, excessive iron is thought to damage the monitoring of cancer cells through these mechanisms. Serum ferritin is widely accepted to be a reactant in the acute phase and a marker of acute and chronic inflammation, and it is known to nonspecifically increase in a variety of inflammatory conditions, including chronic kidney disease, rheumatoid arthritis, and acute infection^20,21. The elevated ferritin in these states reflects an increase in total iron storage throughout the body, but paradoxically, these stores are isolated and cannot be used for hematopoiesis, a process that leads to inflammatory anemia²². The relative lack of iron in inflammation and malignant tumors is speculated to be a defense mechanism that limits the use of serum iron by pathogens and tumors²³. Serum ferritin is elevated in many malignancies^18,24. In neuroblastoma, increased serum ferritin is directly associated with the secretion of ferritin through the tumor²⁵. In our study, the ferritin levels in irAEs induced by ICIs were significantly higher than those in non-irAEs or AEs caused by chemotherapy. The mechanism underlying this phenomenon is unclear and requires further research. Studies on the mechanisms of recently emerging viruses—for instance, severe acute respiratory syndrome corona virus, Middle Eastern respiratory syndrome corona virus, and H7N9, which drive hyper cytokinemia and aggressive inflammation that lead to fatal acute lung injury—have shown that activation of the proinflammatory monocyte/macrophage system plays a crucial role in the development of diseases²⁶. The occurrence and development of GVHD are always accompanied by the activation of the monocyte/macrophage system^27,28. Whether the monocyte/macrophage system can be activated and secrete large amounts of ferritin, thus increasing serum ferritin levels in irAEs induced by ICIs, as in GVHD and severe viral infection, remains to be determined. These hypotheses must be verified and confirmed through in vitro and in vivo experiments.

Conclusions

In conclusion, our data showed that ferritin can be used as a diagnostic, differential diagnostic, and prognostic marker for irAEs in patients with ICI treatment. The mechanism responsible for higher ferritin levels in irAEs induced by ICI than those in non-irAEs or AEs caused by chemotherapy or other therapy must be further studied.

Grant support

This work was supported by grants from the National Key R&D Program of China (Grant No. 2018YFC1313400), the National Major Scientific and Technological Special Project for “Significant New Drug Development” of China (Grant No. 2018ZX09201-015), and the National Natural Science Foundation of China (Grants Nos. 81872487, 81872166, U20A20375, and 81974416).