Risk of Ovarian Cancer in This Clinical Scenario
Based on the clinical features presented—small septated cysts (<2 cm), normal CA-125 levels (20-25 U/mL, well below the 35 U/mL threshold), stability over one year, and absence of concerning imaging features—the probability of ovarian cancer is extremely low, estimated at less than 1-4%. 1, 2, 3
Evidence Supporting Low Malignancy Risk
Reassuring Clinical Features
Cyst size remains small (2 cm initially, 1.7 cm at follow-up), which is significantly below the 5 cm threshold associated with increased malignancy risk in postmenopausal women 1
CA-125 levels are normal (20-25 U/mL), well below the 35 U/mL threshold that has 98.5% specificity for ovarian cancer in women over 50 years 4, 1, 5
One-year stability without growth (September 2024 to September 2025) is a highly reassuring feature suggesting benign etiology 1
CT imaging shows only "follicular changes" without solid components, papillary projections, ascites, or other concerning features that would suggest malignancy 1
Risk Stratification Based on Imaging Characteristics
According to the O-RADS ultrasound risk stratification system, septated cysts without solid components or papillary projections are classified as low risk 1
The presence of thin septations alone (<3 mm) carries a malignancy risk of less than 0.4% 1
The IOTA Simple Rules classify unilocular or septated cysts without solid components >7mm and absence of abnormal blood flow as benign (B) features 1
Supporting Research Evidence
A study of 93 postmenopausal women with ovarian cysts and CA-125 <50 IU/mL found that all 77 patients with CA-125 <35 IU/mL had benign histopathology regardless of tumor size or ultrasound features 2
A 5-year observational study of 226 postmenopausal women with persistent unilocular cysts <50 mm and normal CA-125 found that 76% remained unchanged, and only 3.7% developed malignancy—all of whom had elevated CA-125 levels 3
Research demonstrates that CA-125 has only 50% sensitivity for stage I ovarian cancer, meaning normal levels provide additional reassurance 4, 5
Important Caveats About CA-125
False-positive elevations can occur with endometriosis, pelvic inflammatory disease, benign cysts, adenomyosis, and even menstruation in premenopausal women 4, 1, 6
CA-125 lacks sensitivity for early-stage disease, detecting only about 50% of stage I ovarian cancers, but has nearly 100% specificity when using the 30-35 U/mL threshold 4
The positive predictive value of screening tests is only about 2% in average-risk women, meaning 98% of positive tests are false positives 4
Regarding the Planned Surgery
While the clinical features strongly suggest benign disease, there are legitimate reasons a gynecologic oncologist might recommend surgery in a postmenopausal woman:
Postmenopausal status itself warrants closer evaluation of any persistent ovarian mass, as functional cysts should not occur after menopause 4, 1
Septations, even thin ones, require definitive histologic diagnosis to completely exclude borderline tumors or low-grade malignancies that may have normal CA-125 levels 1
Recurrence of cysts (new 1.7 cm cyst appearing after initial monitoring) may warrant surgical evaluation despite reassuring features 1
Risk-reducing bilateral salpingo-oophorectomy is appropriate for postmenopausal women and eliminates future ovarian cancer risk entirely 4
Critical Clinical Pitfall
Progressive elevation of CA-125 over time, even within the normal range, should prompt concern—however, in this case, CA-125 actually decreased from 25 to 20 U/mL, which is further reassuring 1
The lack of correlation between benign ovarian cyst size and CA-125 elevation suggests that when CA-125 is elevated with benign-appearing cysts, the source may be the fallopian tubes rather than the cyst itself, emphasizing the importance of evaluating the tubes during surgery 7