SPAG9 and ovarian cancer: The members of the CTA family in ovarian cancer mainly include MAGE, GAGE 1/2, LAGE‐1, NY‐ESO‐1, SSX, CT45, and TRAG‐3, which belong to the CT‐X antigen, and AKAP3/4, BAGE, BORIS, OY‐TES‐1(CT23), PRAME, PIWIL, HSP70‐2, SPAG9, and SP17, which belong to non‐X CT antigen.8