BACKGROUND: Immune-related eosinophilia is a new immune related adverse effect associated with anti- PD-1 or anti-PD-L1 treatment (Bernard-Tessier, 2017). It appears to be a rare adverse effect with estimated frequency of 2.9% (Bernard-Tessier, 2017). There is evidence that changes in blood eosinophilia during anti- PD-1 therapy can be a predictor of long-term disease control in metastatic melanoma (Gaba, 2015). At least 3 studies have correlated immune mediated eosinophilia with high overall response rates up to 69% (Bernard- Tessier, 2017; Gaba, 2015; A, 2017). With this interesting observation, we retrospectively reviewed 36 patients in our center who were treated with PD-1 and anti PD-L1 agents. The Objective of our review was to assess the correlation of eosinophilia with the complete response rate.
METHODS: We retrospectively reviewed the medical records of 36 patients from May 2016 -May 2020 who had received anti PD-1 or anti PD-L1 treatment for metastatic solid tumors. Patients who had received consolidation immunotherapy were excluded from the review. Absolute Eosinophil Count (AEC) of over 500 per mm3 was used to define eosinophilia. Incidence rate of eosinophilia was estimated in comparison to the total number of patients who had received the above treatments.
RESULTS: In this small single center cohort of 36 male patients, eosinophilia was observed in 4/36 patients (11.11%). The median time to the absolute eosinophilia was 24 weeks (3 weeks - 52 weeks). Three out of the 4 patients had complete response. Complete response rates in patients with eosinophilia at any point after initiation of immunotherapy was 75% compared with 2.7% in the noneosinophila group. Overall response rate was 75% (3/4) in the eosinophilia group vs 12.5% (4/32) in the noneosinophilia group.
CONCLUSIONS: In our small retrospective cohort of patients, immune-related eosinophilia with anti-PD-1 and anti-PD-L1 treatments appear to be a biomarker and associated with beneficial clinical response. Additional, larger prospective studies are required to validate this. If validated in prospective studies, immune related eosinophilia could serve as a cost effective biomarker to identify responders likely to derive long-term disease control with immune therapies.