Risk of Malignancy in Unilocular Ovarian Cystic Tumors Less Than 10 Centimeters in Diameter Susan C. Modesitt, MD, Edward J. Pavlik, PhD, Frederick R. Ueland, MD, Paul D. DePriest, MD, R. J. Kryscio, PhD, and J. R. van Nagell, Jr, MD OBJECTIVE: To determine the natural history and to esti- mate the risk of malignancy of unilocular ovarian cystic tumors less than 10 cm in diameter followed conservatively by transvaginal ultrasound. METHODS: From 1987 to 2002, 15,106 asymptomatic women at least 50 years old entered the University of Kentucky’s Ovarian Cancer Screening Program and underwent initial transvaginal ultrasonography. If the screen revealed noth- ing abnormal, women were asked to repeat transvaginal ultrasonography yearly. If the screen revealed abnormali- ties, transvaginal ultrasonography was repeated in 4 to 6 weeks, along with Doppler flow ultrasonography and CA 125 testing. RESULTS: Of the 15,106 women at least 50 years old, 2763 women (18%) were diagnosed with 3259 unilocular ovar- ian cysts. A total of 2261 (69.4%) of these cysts resolved spontaneously, 537 (16.5%) developed a septum, 189 (5.8%) developed a solid area, and 220 (6.8%) persisted as a uniloc- ular lesion. During this time, 27 women received a diagno- sis of ovarian cancer, and ten had been previously diag- nosed with simple ovarian cysts. All ten of these women, however, developed another morphologic abnormality, ex- perienced resolution of the cyst before developing cancer, or developed cancer in the contralateral ovary. No woman with an isolated unilocular cystic ovarian tumor has devel- oped ovarian cancer in this population. CONCLUSION: The risk of malignancy in unilocular ovarian cystic tumors less than 10 cm in diameter in women 50 years old or older is extremely low. The majority will resolve spontaneously and can be followed conservatively with serial transvaginal ultrasonography. (Obstet Gy- necol 2003;102:594 –9. © 2003 by The American College of Obstetricians and Gynecologists.) Ovarian cancer is the second most common gynecologic malignancy in the United States and is the fifth leading cause of cancer death among US women. 1 Most women are diagnosed with advanced-stage cancer and undergo extensive surgical debulking, followed by combination chemotherapy. Initial complete response to therapy can be achieved in most women; however, relapse is the rule, and once ovarian cancer recurs, it is almost universally fatal. The dismal outcomes associated with the diagnosis of ovarian cancer in advanced stages has prompted the investigation of potential screening methods in an effort to detect the cancer at an earlier stage and to decrease mortality. The use of transvaginal ultrasonography for ovarian cancer screening has been increasing in recent years. Sonography is also routinely performed in patients whose clinical examinations reveal ovarian enlargement. Transvaginal ultrasonography is a sensitive procedure that tests for ovarian abnormalities. It has limited inter- observer variability but low positive predictive value. 2–4 As a result of the increasing use of sonography, the diagnosis of unilocular ovarian cysts in postmenopausal women has been increasing. Women with cystic ovarian tumors had been treated surgically until it was recog- nized that the malignant potential of a simple cyst was extremely low. 5,6 The purpose of this study was to determine this disease’s natural history and to estimate the risk of malignancy of unilocular cystic ovarian tu- mors 10 cm or less in diameter in women at least 50 years old followed conservatively by transvaginal sonogra- phy. MATERIALS AND METHODS From 1987 to 2002, a total of 18,464 women were enrolled onto the University of Kentucky’s Ovarian Cancer Screening Program, and 15,106 of these women were at least 50 years old. Eligibility criteria for the screening program included the following: all women at least 50 years old, or women at least 25 years old with a documented family history of ovarian cancer in at least one primary or secondary relative. All study participants completed a questionnaire regarding medical history From the Division of Gynecologic Oncology, Department of Obstetrics and Gyne- cology, and Department of Statistics, University of Kentucky Markey Cancer Center, Lexington, Kentucky. Supported in part by a grant from the Abercrombie Foundation and the R. L. Telford Foundation. 594 VOL. 102, NO. 3, SEPTEMBER 2003 0029-7844/03/$30.00 © 2003 by The American College of Obstetricians and Gynecologists. Published by Elsevier. doi:10.1016/S0029-7844(03)00670-7