Since the middle twenties it has been pointed out that ovarian endometriosis may undergo malignant transformation. Long and Taylor,1 in 1964, in reviewing 120 cases of primary cancer of the ovary, found several cases of primary ovarian adenocarcinoma which structurally resembled an adenocarcinoma of the endometrium. They postulated that this tumor might have its origin in benign endometriosis and, when compared to other malignant tumors, considered the prognosis relatively favorable. This report, as well as earlier communications by other authors, revived interest in malignant transformation of ovarian endometriosis.
Recently, Fathalla2 surveyed 418 primary malignant ovarian tumors, and of these he was able to classify 52 with a histological appearance similar to that of malignant tumors of the uterine endometrium. In his series, the malignant endometrioid tumors accounted for approximately 12% of all primary malignant tumors of the ovary. Two specimens of adenoacanthoma and two of endometrioid carcinoma had