Cancer of the testis. Light micrograph of cells of the human testis showing abnormal development of gonocyte cells caused by carcinoma in situ (also called intratubular germ cell neoplasia). The abnormal cells are pale coloured with irregularly shaped central nuclei. Gonocytes are the precursors of sperm cells. There is no normal sperm production in these cells. Carcinoma in situ is thought to arise during foetal life and it is a risk factor for the development of other forms of testicular cancer in later life. The cells may metastasize to other regions of the body where they cause secondary cancer. Magnification: x370 when printed 10cm wide.