The present invention provides an antibody or an antigen-binding fragment thereof with binding specificity for human interleukin-1 receptor accessory protein (IL1RAP) wherein the antibody or antigen-binding fragment is capable of inhibiting the binding of antibody ‘CAN04’ to human IL1RAP. The invention further provides the use of such antibodies or an antigen-binding fragments in the treatment and/or diagnosis of IL-1 associated diseases and conditions, including cancers such as acute myeloid leukemia and melanoma.