Additionally, these authors were able to show that, in two cases of OCCC with available adjacent atypical as well as distant endometriosis, identical ARID1A mutations were found in the cancer and the adjacent endometriosis but were absent in the distant endometriotic lesions, implying that ARID1A mutations play a role in the malignant transformation of endometriosis. The gene discussed is ARID1A; the disease is endometriosis.