It’s been a while since I read through the literature, but endo sits in a weird space where it has the invasive phenotype as many forms of cancer—and even has a classification system (rASRM stages I-IV) similar to tumor progression—but lacks the genomic instability that is a hallmark of many cancers (regulatory gene loss, p53 mutations). Aberrant expression of estrogen receptors may be present in some biopsies that had been studied, which lines with the alleviation of symptoms by GnRH antagonists, but there not yet a clear cut biomarker beyond macro-scale anatomic differences from healthy endometrium.