Estrogen, in the males, is formed by the peripheral aromatization of testosterone in the adipose, brain, skin, and bone.  Its role in spermatogenic maturation is still being delineated.  In excess levels it will inhibit GnRH and LH release.  It is not routinely tested in the evaluation of testicular reserve following cancer therapy but is a lab value often checked in the clinical evaluation of an infertile male.