In order for any hormone to act on a cell, there must be a hormone receptor. The type of receptor is determined by the type of hormone. There are two types of hormones. Steroids are lipid soluble hormones that can enter the cell cytoplasm by diffusion and act through a steroid hormone receptor. This initiates the signal transduction pathway.
Kinases are a common component of signal transduction pathways.
Ras is a protein found in the signal transduction pathway which is important in human cancers. In its inactive form, Ras-GDP, the MAP kinase pathway is not activated by the receptor. This is a dominant mutation. Therefore, there are several ways external controls over the cell cycle can be changed to stimulate cell division inappropriately and contribute to the progression of a normal cell to cancer. The hormone-growth factor might be present when it shouldn't be and send inappropriate messages to the cell to replicate.