Spontaneous regression of metastatic renal cell carcinoma (mRCC) is a rare event, often associated with an activation of innate immunity by various triggers. SARS-CoV-2 infection induces a strong inflammatory response in some patients and a cytokine storm is one of the main causes of severe morbidity and mortality associated with the virus. Here, we describe two cases of patients with histologically and radiologically proven mRCC whose treatment was delayed due to COVID-19 and who experienced spontaneous tumour regression following the infection. Both patients reported here had predominantly pulmonary and mediastinal involvement and underwent nephrectomy. The interval between the diagnosis of COVID-19 and the detection of tumour regression was 3 and 4 months, respectively. Although approved vaccines and other measures are clearly the best way to prevent COVID-19-associated morbidity and mortality in cancer patients, we hypothesize that innate immunity activation by the infection can contribute to tumour regression in special circumstances.

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