Elevated Eosinophil Count Following Pembrolizumab Treatment for Non-Small Cell Lung Cancer

The multidisciplinary approach to eosinophilia

Eosinophilic granulocytes are normally present in low numbers in the bloodstream. Patients with an increased number of eosinophilic granulocytes in the differential count (eosinophilia) are common and can pose a clinical challenge because conditions with eosinophilia occur in all medical specialties. The diagnostic approach must be guided by a thorough medical history, supported by specific tests to guide individualized treatment. Neoplastic (primary) eosinophilia is identified by one of several unique acquired genetic causes. In contrast, reactive (secondary) eosinophilia is associated with a cytokine stimulus in a specific disease, while idiopathic eosinophilia is a diagnosis by exclusion. Rational treatment is disease-directed in secondary cases and has paved the way for targeted treatment against the driver in primary eosinophilia, whereas idiopathic cases are treated as needed by principles in eosinophilia originating from clonal drivers. The vast majority of patients are diagnosed with secondary eosinophilia and are managed by the relevant specialty-e.g., rheumatology, allergy, dermatology, gastroenterology, pulmonary medicine, hematology, or infectious disease. The overlap in symptoms and the risk of irreversible organ involvement in eosinophilia, irrespective of the cause, warrants that patients without a diagnostic clarification or who do not respond to adequate treatment should be referred to a multidisciplinary function anchored in a hematology department for evaluation. This review presents the pathophysiology, manifestations, differential diagnosis, diagnostic workup, and management of (adult) patients with eosinophilia. The purpose is to place eosinophilia in a clinical context, and therefore justify and inspire the establishment of a multidisciplinary team of experts from diagnostic and clinical specialties at the regional level to support the second opinion. The target patient population requires highly specialized laboratory analysis and therapy and occasionally has severe eosinophil-induced organ dysfunction. An added value of a centralized, clinical function is to serve as a platform for education and research to further improve the management of patients with eosinophilia. Primary and idiopathic eosinophilia are key topics in the review, which also address current research and discusses outstanding issues in the field.

Tumor-associated eosinophilia in a patient with EGFR-positive, MET-amplified lung adenocarcinoma refractory to targeted therapy: a case report and review of literature

Paraneoplastic eosinophilia is a rare complication observed in 1% solid tumor cases and appears to have tumor type-dependent prognostic impact, in which the increased eosinophil count was generally associated with unfavorable prognosis. In the English literature, more than 20 patients have been reported of eosinophilia associated with primary non-small cell lung cancer (NSCLC) at diagnosis, all of whom underwent either surgery, chemotherapy, or symptomatic therapy. Herein, we describe clinical course a stage IV NSCLC patient with paraneoplastic eosinophilia and leukocytosis and receiving targeted therapy. A 64-year-old male former smoker was diagnosed with lung adenocarcinoma harboring EGFR L858R mutation and MET amplification. Blood eosinophilia was manifested at diagnosis and confirmed to be paraneoplastic by eliminating other potential causes. The disease progressed rapidly within a month on EGFR inhibitor icotinib and then within three months on icotinib plus crizotinib after rapid response within the first month. A multi-target kinase inhibitor anlotinib was added, and the disease progressed one month later despite initial self-reported asymptomatic high-performance status. The patient was lost to subsequent follow-ups. Radiographic evaluation of disease control or progression coincided with respective distinct alleviation or worsening of eosinophilia. Consistent with previous reports of poor clinical outcome associated with blood eosinophilia, our results suggested a negative prognostic impact in EGFR-/MET-altered NSCLC. This case is, to the best of our knowledge, the first to provide evidence for blood eosinophilia paralleling disease progression in an EGFR- and MET-altered lung adenocarcinoma under targeted therapy, which suggested negative prognostic impact of blood eosinophilia in driver-positive NSCLC.

Bridging the Gap: Connecting the Mechanisms of Immune-Related Adverse Events and Autoimmunity Through PD-1

The emergence of anti-cytotoxic T-lymphocyte antigen 4 (anti-CTLA-4), anti-programmed cell death 1 ligand (anti-PD-1), and anti-PD-L1 antibodies as immune checkpoint inhibitors (ICIs) revolutionized the treatment of numerous types of tumors. These antibodies, both alone and in combination, provide great clinical efficacy as evidenced by tumor regression and increased overall patients' survival. However, with this success comes multiple challenges. First, while patients who respond to ICIs have outstanding outcomes, there remains a large proportion of patients who do not respond at all. This all-or-none response has led to looking downstream of programmed cell death 1 (PD-1) for additional therapeutic targets and for new combination therapies. Second, a majority of patients who receive ICIs go on to develop immune-related adverse events (irAEs) characterized by end-organ inflammation with T-cell infiltrates. The hallmarks of these clinically observed irAEs share many similarities with primary autoimmune diseases. The contribution of PD-1 to peripheral tolerance is a major mechanism for protection against expansion of self-reactive T-cell clones and autoimmune disease. In this review, we aim to bridge the gaps between our cellular and molecular knowledge of PD-1 signaling in T cells, ICI-induced irAEs, and autoimmune diseases. We will highlight shared mechanisms and the potential for new therapeutic strategies.