A case report of eyelid Merkel cell carcinoma occurring under treatment with nivolumab for a lung adenocarcinoma 11 Medical and Health Sciences 1112 Oncology and Carcinogenesis

Background: Merkel cell carcinoma (MCC) is a rare neuroendocrine malignancy of the skin characterized by high aggressiveness. Four main factors are implicated in its development: immunosuppression, ultraviolet radiation, age and the Merkel cell polyomavirus (MCPyV). In recent years, immune checkpoint inhibitors have shown clinical activity in MCC treatment. Case presentation: We report the case of an 82-year-old man with a lung adenocarcinoma diagnosis, who underwent immunotherapy with nivolumab as second-line treatment. Seven months after the diagnosis of lung cancer during the nivolumab treatment, the patient developed an eyelid MCC, initially misdiagnosed as a chalazion. A palliative radiotherapy was performed with clinical benefit. After a total of seven cycles of nivolumab, computed tomography showed a lung and cerebral disease progression. In addition, clinical conditions worsened leading to the patient's death 13 months after the initial lung cancer diagnosis. Conclusions: Cases of co-occurrence of MCC and non-small cell lung cancer (NSCLC) have rarely been reported. Interestingly, common risk factors may be postulated for both cancers. Considering the rarity of this adverse event, its short-term temporal relation with the administration of the drug, which makes a relation improbable, and the coexistence of other risk factors, which may provide plausible explanations, it is possible to conclude according to the WHO Adverse Reaction Terminology that a causal relation between the occurrence of this serious adverse event and the exposure to the drug is unlikely. However, the case deserves to be reported in the literature.