IL2 and cancer: Hyponatremia, defined as a serum sodium level below 135 mEq/L (to convert to millimoles per liter, multiply by 1), is an independent prognostic factor for various solid malignant tumors including RCC.14,15,16,17 It has been associated with a poorer outcomes and shorter cancer-specific survival in patients with mRCC treated with several types of drugs, including TKIs, mammalian target of rapamycin–targeted agents,18 interleukin-2, and interferon-α.19 However, to our knowledge, no associations with ICI in mRCC have been previously reported.