INHBA (inhibin beta A) is a protein subunit that joins other subunits to form both activin and inhibin. Inhibin is a pituitary FSH secretion inhibitor that negatively regulates gonadal stromal cell proliferation and participates in tumor suppression. Inhibin serum levels have been shown to reflect the size of granulosa-cell tumors and be used as a marker for primary as well as recurrent disease. Because expression in gonadal and various extragonadal tissues may vary severalfold in a tissue-specific fashion, it is proposed that inhibin may be both a growth/differentiation factor and a hormone. INHBA forms a homodimer, activin A, and also joins with beta B subunit to form a heterodimer, activin AB, both of which stimulate FSH secretion. References: The UniProt Consortium. Nucleic Acids Res. 47: D506-515 (2019); Nucleic Acids Res. 2016 Jan 4;44(D1):D733-45, PMID:26553804;