Lymphopenia as a hematological immune-related adverse event would be in line with the fact that the frequency was significantly higher in patients treated with combined immunotherapy with ipilimumab and nivolumab, which is known to be associated with higher rates of severe immune-related adverse events compared to treatment with anti-PD1- or anti-CTLA-4 antibodies alone [3]. This evidence concerns the gene CTLA4 and lymphopenia.