Cytokines (Greek cyto-, cell; and -kinos, movement) are small cell-signaling protein molecules that are secreted by numerous cells and are a category of signaling molecules used extensively in intercellular communication. Cytokine signaling is involved in malignancy.

A Growth factor is a naturally occurring substance capable of stimulating cellular growth, proliferation and cellular differentiation. Usually it is a protein or a steroid hormone. In tumor cells excessive growth factors stimulates irregular proligeration.  Overproduction of growth factors is a common feature of tumor cells, stimulating inappropriate and unregulated proliferation.

A hormone (from Greek ὁρμή, "impetus") is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism.