Is a PET (Positron Emission Tomography) scan necessary to determine if ovarian cancer, possibly associated with endometriosis, has spread in a recently diagnosed patient?

Is PET Scan Necessary for Initial Staging of Ovarian Cancer?

No, PET scan is not necessary for initial staging of newly diagnosed ovarian cancer—CT of the chest, abdomen, and pelvis with IV contrast is the primary recommended imaging modality. 1, 2, 3

Primary Imaging Recommendation

CT thorax, abdomen, and pelvis with IV contrast should be obtained as the first-line staging study after diagnosis of suspected advanced ovarian cancer. 1, 2 This provides comprehensive assessment of:

• Peritoneal implants and omental involvement 2, 3
• Lymph node metastases 2
• Pleural disease and pulmonary metastases 2
• Distant metastases 2
• Tumor resectability for surgical planning 1, 3

The 2025 ASCO guidelines explicitly recommend CT of abdomen/pelvis with oral and IV contrast (if not contraindicated) plus chest imaging (CT preferred) as the standard primary clinical evaluation. 1

Why PET Scan Is NOT Recommended for Initial Staging

The American College of Radiology does not recommend PET/CT for initial staging due to low specificity (as low as 54%) and potential for both false-negative and false-positive results. 2 Key limitations include:

• False-negative results occur with borderline tumors, mucinous tumors, early carcinomas, and low-grade histologic types 3
• False-positive results occur with fibromas, dermoid cysts, hydrosalpinges, and endometriosis 3
• This is particularly relevant given your patient's possible endometriosis association, which can cause false-positive PET findings 3

When PET/CT May Be Useful (As an Adjunct Only)

PET/CT should be considered only in specific scenarios as a conditional recommendation: 1

• When CT findings are indeterminate or inconclusive 1, 2, 3
• For detecting small peritoneal deposits when CT is equivocal 2, 3
• For evaluating lymph node involvement when CT is uncertain 2
• In recurrent disease with rising CA-125 but negative/equivocal CT 3

The 2025 ASCO guidelines list FDG-PET scan as a conditional recommendation (moderate evidence quality) that may be used to refine assessment after initial CT, but not as a replacement for CT. 1

Other Imaging Modalities to Consider

Diffusion-weighted MRI is also listed as a conditional recommendation and may be particularly useful for: 1

• Borderline tumors 2
• Young patients requiring fertility preservation 2
• Suspected endometriosis-associated malignancy 2
• When CT findings are inconclusive 2

MRI has equivalent accuracy to CT (82-84%) for staging but is reserved for specific scenarios rather than routine use. 2

Critical Pitfalls to Avoid

• Do not skip chest imaging—CT chest is essential for detecting pleural effusions and pulmonary metastases that upstage disease to Stage IV and alter surgical planning 2
• Ensure IV contrast is administered unless contraindicated, as contrast is essential for detecting and characterizing tumor deposits and assessing vascular involvement 2
• Do not rely on ultrasound alone for comprehensive staging, as it is insufficient 3

Special Consideration for Endometriosis-Associated Ovarian Cancer

Given the possible endometriosis association in your patient, note that:

• Endometriosis-associated ovarian cancers are more likely to be confined to the pelvis (54% vs 9%) and lower grade 4
• These cancers are particularly associated with clear cell and endometrioid histologic types 5, 6, 7
• Women with ovarian endometriomas have markedly increased ovarian cancer risk, especially for type I ovarian cancers 8
• PET scan's false-positive rate with endometriosis makes it even less appropriate for initial staging in this population 3

Surveillance Context (Not Initial Staging)

For completeness, while not applicable to your newly diagnosed patient, PET-CT shows 45-100% sensitivity for detecting recurrent ovarian cancer during surveillance, compared to 40-93% for CT alone. 1 However, this data pertains to recurrence detection, not initial staging. 1