The CHI3L1 protein was originally discovered in mouse breast cancer cells.19 More recently, this chitinase‐like protein has been directly associated with the progression and aggressiveness of PCa.20 Although not previously described as a secreted product of monocytes, we discovered that conditioned supernatants from PCa monocytes (and macrophages from the same patients; not shown) contain significant amounts of CHI3L1. Here, CHI3L1 is linked to breast cancer.