The present invention provides GPR56 genes and polypeptides encoded therefor. The GPR56 genes of the invention are expressed highly in malignant tissues and the invention also provides diagnostic processes for detecting cancer or malignant tumors in human subjects The diagnostic and prognostic test of the present invention is particularly useful for the early detection of ovarian cancer or metastases thereof and for monitoring the progress of disease, such as, for example, during remission or following surgery or chemotherapy. The GPR56 gene of the invention is also expressed in effector memory T cells, and the invention therefor provides methods of identifying and/or quantifying effector memory T cells, which methods are useful for determining the immune status of a subject.