CD44 and Leydig cell tumor: However, after backcrossing for more than 20 generations from the original C57BL/6 background to the SJL/J background, the resultant autochthonous tumors clearly showed morphologic and histologic characteristics more consistent with Leydig cell tumors and expressed the luteinizing hormone receptor (LHR), a cell surface marker traditionally associated with Leydig cells rather than Sertoli cells [17].