Testis-specific protein on Y chromosome (TSPY1) is an ampliconic gene on the Y chromosome that has been associated with gonadoblastoma. Recent experiments have shown that in androgen-dependent testicular germ-cell tumors, TSPY1 can repress the androgen-bound androgen receptor (AR), a member of the nuclear steroid hormone receptor family that acts as a ligand-inducible transcription factor, suggesting that TSPY1 is a repressor of cell proliferation in germ-cell tumors and potentially in normal gonadal cells during early development. Two distinct isoforms of TSPY1, TSPY1L and TSPY1S, are known to exist.Synonyms: CT78, Cancer/testis antigen 78, Testis-specific Y-encoded protein 1