TESTICULAR INTRAEPITHELIAL NEOPLASIA - THE PRECURSOR OF TESTICULAR GERM-CELL TUMORS

Testicular intraepithelial neoplasia (TIN; so-called carcinoma in situ of the testis) is the uniform precursor of testicular germ-cell tumor s. TIN is derived from embryonal gonocytes and is present in the testi s of a future testis cancer patient at the time of birth. TIN spreads inside the seminiferous tubules until it progresses to invasive cancer . Diagnosis is best achieved by surgical biopsy of the testis and subs equent immunohistological staining of placental alkaline phosphatase. This enzyme is present in gonocytes, TIN, and seminoma as well as in s everal other types of germ-cell tumors but not in normal germ cells. T IN is found in testicular tissue adjacent to testicular germ-cell tumo rs and is observed in all clinical groups known to be at risk for test icular cancer: cryptorchidism (2-3%), infertility (1%), ambiguous geni talia (25%), in contralateral testis of patients with testis cancer (3 -6%). Conversely, TIN is not found in the normal male population. If T IN is left untreated, there is a 50% probability of progressing to fra nk germ-cell neoplasm within 5 years. Localized radiotherapy to the te stis with 18-20 Gy eradicates TIN and germ cells while Leydig cells ar e preserved. The patient can thus be spared orchiectomy and hormone su pplementation. The concept of TIN offers the chance of very early dete ction of testis cancer and organ-preserving early treatment.