A two-way ANOVA analysis evidenced a statistically significant effect of the interaction of endometriosis and metformin treatment on ET-1 expression [F (1.28) = 7.94, p < 0.01]; when performing multiple t-tests per row, a decrease in ET-1 expression in group ME comparatively with group E (p = 0.03) was found. Here, EDN1 is linked to endometriosis.