What is the investigation of choice for a post-menopausal obese female with elevated Cancer Antigen 125 (CA 125) levels and gastrointestinal features suggestive of ovarian cancer?

Investigation of Choice for Suspected Ovarian Cancer in a Postmenopausal Woman

Transvaginal ultrasonography (TVUS) is the investigation of choice for a postmenopausal obese female with elevated CA-125 and gastrointestinal features suggestive of ovarian cancer. 1

Primary Diagnostic Approach

Transvaginal Ultrasound as First-Line Imaging

• Ultrasonography of the abdomen and pelvis is the first imaging investigation recommended when ovarian cancer is suspected, with transvaginal ultrasonography providing superior visualization of ovarian structures compared to transabdominal approaches. 1

• TVUS should include color or power Doppler to assess vascularity patterns and differentiate true solid components from debris. 2

• Specific morphological features highly suggestive of malignancy include: large lesions, multi-locular cysts, solid papillary projections, irregular internal septations, and ascites. 1

• In postmenopausal women with elevated CA-125 and abnormal ovarian morphology on ultrasound, the cumulative risk of ovarian cancer reaches 24%, representing a 327-fold increased relative risk compared to those with normal ultrasound findings. 3

Role of CA-125 in Conjunction with Imaging

• While CA-125 is elevated in approximately 85% of advanced ovarian cancer cases, it has only 50% sensitivity for stage I disease, making imaging essential for diagnosis. 1

• The combination of CA-125 elevation and abnormal ultrasound findings provides substantially higher diagnostic accuracy than either test alone. 3

Additional Tumor Markers to Consider

Distinguishing Ovarian from Gastrointestinal Origin

Given the gastrointestinal features in this patient, additional tumor markers are warranted:

• Serum CEA and CA 19-9 should be measured when it is unclear whether an ovarian mass is of gastrointestinal origin or a primary mucinous ovarian tumor. 1

• A CA-125/CEA ratio ≤25 suggests possible gastrointestinal origin and warrants consideration of colonoscopy and/or gastroscopy. 1, 4

• CA-125/CEA ratio >25 favors ovarian origin over gastrointestinal origin. 4

When Cross-Sectional Imaging is Indicated

CT Scanning

• CT scanning is not useful as a preoperative staging tool and should not be performed routinely for initial diagnosis. 1

• Cross-sectional imaging with CT is essential for guiding surgical planning when ovarian cancer is suspected based on ultrasound findings, but it follows rather than replaces ultrasound as the initial investigation. 1

MRI Considerations

• MRI is superior to CT for characterizing adnexal masses and should be considered when ultrasound findings are indeterminate, not as a first-line investigation. 2

• MRI with IV contrast is the next step for cysts that become indeterminate on ultrasound. 2

Endoscopic Evaluation

• Colonoscopy and/or gastroscopy should be considered when the CA-125/CEA ratio is ≤25 or when gastrointestinal symptoms are prominent, to exclude a primary gastrointestinal malignancy with ovarian metastases. 1

• This is particularly important in this patient given the presence of gastrointestinal features. 1

Important Clinical Caveats

Obesity Considerations

• While obesity may limit transabdominal ultrasound quality, transvaginal ultrasonography remains highly effective and is not significantly impaired by body habitus. 1

False Positive CA-125 Elevations

• CA-125 can be elevated in non-gynecological malignancies (breast, lung, colon, pancreatic cancer) and benign conditions (endometriosis, pelvic inflammatory disease, ovarian cysts), emphasizing why imaging confirmation is essential. 1

• In women aged ≥50 years with CA-125 ≥35 U/ml who do not have ovarian cancer, 20.4% are diagnosed with a non-ovarian cancer, making thorough evaluation critical. 5

Postmenopausal Status

• Postmenopausal status itself warrants closer evaluation of any persistent ovarian mass, as functional cysts should not occur after menopause. 2

Diagnostic Algorithm Summary

1. Perform transvaginal ultrasonography with color Doppler as the initial investigation 1
2. Measure serum CEA and CA 19-9 in addition to CA-125 (already obtained) to assess for gastrointestinal origin 1
3. Calculate CA-125/CEA ratio: if ≤25, proceed with colonoscopy/gastroscopy 1
4. If ultrasound shows concerning features (solid components, papillary projections, thick septations, ascites), proceed to surgical exploration for definitive diagnosis and staging 1
5. If ultrasound findings are indeterminate, consider MRI with IV contrast for further characterization 2