Immune checkpoint inhibitors and the orbit; two cases of reactive dacryoadenitis

Immune checkpoints refer to mechanisms entrusted with the modulation of immune responses in peripheral tissues and are required for minimising collateral damage. Immune checkpoint inhibitors (ICPi) work through numerous pathways, including the anti-CTLA-4 (cytotoxic T-lymphocyte-associated protein 4), anti-PD-1 (programmed cell death protein 1) and the PD-L1 (protein cell death protein-ligand-1) pathways. They are proving to be an exciting therapeutic avenue in the attempt to activate anti-tumour activity. Ipilimumab is a fully human monoclonal antibody working on the anti-CTLA-4 pathway, while nivolumab and pembrolizumab are humanised monoclonal IgG4 antibodies that work on the PD-1 pathway. Despite a growing body of research pertinent to these novel therapies, early indications show that they are limited by their side effect profile. Furthermore, their efficacy appears to be greater in cancers with a high mutational burden. We present two female patients with bilateral reactive dacryoadenitis secondary to ICPi therapy, a finding that to the best of our knowledge was not previously described in the literature.