In one study, clomiphene citrate was used to treat infertile men with NOA; subsequent testicular sperm extraction showed that most tubules (>70%) exhibited no tubular lumen or regular seminiferous epithelium, but there were a large number of spermatogonia-like cells that exhibited normally differentiated spermatogonia with enhanced proliferation activity (positive for PCNA) [78]. Here, PCNA is linked to Infertility.