Is a Positron Emission Tomography (PET) Computed Tomography (CT) scan effective for screening for cancer relapse in a patient with a history of cancer?

PET/CT for Cancer Relapse Screening

PET/CT is NOT recommended for routine surveillance screening in asymptomatic cancer patients after curative treatment, but it IS highly effective when there is clinical suspicion of recurrence, equivocal conventional imaging findings, or rising tumor markers. 1, 2

Key Distinction: Screening vs. Diagnostic Evaluation

The critical issue is understanding the difference between routine surveillance (screening asymptomatic patients) versus targeted evaluation (investigating suspected recurrence):

NOT Recommended for Routine Screening

• The American Society of Clinical Oncology explicitly states PET/CT should not be used for routine breast cancer surveillance in asymptomatic patients, as there is no evidence of survival benefit, quality of life improvement, or cost-effectiveness from early detection of asymptomatic metastases 1, 2
• This recommendation extends to other cancer types where patients have been treated with curative intent and remain asymptomatic 1
• The false-positive rate is 11% even in patients with known malignancy, leading to unnecessary anxiety and interventions 2

Highly Recommended When Recurrence is Suspected

PET/CT demonstrates excellent diagnostic performance when used appropriately:

• Sensitivity: 85-94% and specificity: 81-100% for detecting recurrent disease across multiple cancer types 1, 3
• Changes clinical management in 40-50% of patients when conventional imaging is equivocal or tumor markers are rising 1

Cancer-Specific Recommendations for Suspected Recurrence

Breast Cancer

• Use PET/CT when conventional imaging (CT, MRI, ultrasound, bone scan, mammography) shows equivocal findings or when tumor markers (CA 15.3 or CEA) are rising 1
• Pooled diagnostic performance: sensitivity 0.90, specificity 0.81, area under ROC curve 0.94 1
• PET/CT changed treatment modality or intent in 48% of patients with suspected breast cancer relapse 1
• Can detect recurrence even when tumor markers are negative if clinical suspicion exists 1

Colorectal Cancer

• Recommended as first choice in patients with increased suspicion of recurrence, particularly when CEA is elevated but CT is negative 1
• Sensitivity 92% and specificity 100% for detecting recurrent colorectal cancer 4
• Particularly valuable for assessing operability of recurrent disease and liver metastases when CT/MRI is equivocal 1

Lung Cancer

• PET/CT is preferred after chest CT provides suspicion of relapse, per NCCN guidelines 1
• Sensitivity ranges 80.8-94.4% and specificity 62.0-97.6% for detecting recurrent non-small cell lung cancer 1
• Superior for detecting extrathoracic recurrence compared to CT alone 1

Melanoma

• Recommended for screening recurrence in high-risk patients (Stage III) as part of follow-up 1
• Most accurate method for identifying melanoma metastases in patients with high-risk metastatic disease 1
• Detects unrecognized metastases leading to altered management in 10-19% of patients 1

Cervical Cancer

• Sensitivity 85.7% and specificity 86.7% for detecting recurrent cervical cancer 3
• Recommended for response evaluation and as predictor of event-free and overall survival 1
• Use when there is clinical suspicion or equivocal conventional imaging 1

Head and Neck Cancer

• Identifies at least 30% of primary tumors not detected by conventional means in unknown primaries 1, 5
• Recommended in diagnostic work-up when recurrence is suspected 1

Clinical Algorithm for PET/CT Use in Suspected Recurrence

Use PET/CT when ANY of the following criteria are met:

1. Rising tumor markers with negative or equivocal conventional imaging (e.g., CEA in colorectal cancer, CA 15.3 in breast cancer) 1

2. Equivocal findings on CT or MRI that require clarification before treatment decisions 1

3. Clinical symptoms suspicious for recurrence (new pain, neurological symptoms, unexplained weight loss) with negative conventional imaging 1

4. Differentiating post-treatment fibrosis from viable tumor tissue, where PET/CT excels 1

5. Assessing operability of suspected recurrent disease, particularly for liver metastases or isolated lesions 1

Important Caveats and Limitations

False-Negative Scenarios

• Subcentimeter lesions (<1 cm) due to poor spatial resolution 5
• Certain tumor types with low FDG uptake: bronchoalveolar carcinomas, mucinous tumors, well-differentiated neuroendocrine tumors 5
• Micrometastases in lymph nodes (sensitivity only 14-47%) 5

False-Positive Scenarios

• Inflammatory conditions, infections, and benign tumors can show FDG uptake 5
• Post-treatment inflammation in the first 3 months after radiation or surgery 1
• Always obtain tissue confirmation when feasible, especially if management will change 2

Practical Implementation

When PET/CT detects suspected recurrence:

1. Obtain tissue confirmation when technically feasible, as receptor status can change from primary tumor in 20-30% of cases (particularly important in breast cancer) 2

2. Complete staging with additional imaging: If systemic metastases are confirmed, add brain MRI (for breast, lung, melanoma) and complete abdominal imaging 2, 6

3. Perform PET/CT on EARL or ACR/IAC certified scanners and report using standardized criteria (PERCIST, EORTC) for response assessment 1

The evidence strongly supports PET/CT as a powerful diagnostic tool for suspected recurrence, but it should never replace clinical judgment or be used for routine screening in asymptomatic patients where it provides no survival benefit. 1, 2