In an adult patient in remission for almost two years with a normal PET (positron emission tomography) scan at 1 year 9 months, how should the next PET scan be scheduled?

PET Scan Surveillance After 1 Year 9 Months in Remission

No further routine PET scans should be scheduled—routine surveillance PET imaging is explicitly not recommended for patients in remission from lymphoma. 1, 2

Why Routine PET Surveillance is Discouraged

The ESMO (European Society for Medical Oncology) guidelines for diffuse large B-cell lymphoma explicitly state that "routine surveillance with PET scan is not recommended" 1. This recommendation is echoed across multiple lymphoma types and is based on several critical factors:

• High false-positive rates: PET scans in asymptomatic patients generate false-positives that lead to unnecessary biopsies, anxiety, and radiation exposure 3, 4
• No survival benefit: There is no definitive evidence that routine imaging in patients in complete remission provides any outcome advantage 1
• Increased secondary malignancy risk: Repeated imaging may increase the incidence of secondary malignancies 1
• Poor positive predictive value: Research demonstrates that while PET has excellent sensitivity (100%) and negative predictive value (100%), the positive predictive value is only 18.2% in post-treatment surveillance 4

Recommended Surveillance Strategy Instead

Clinical follow-up should consist of history and physical examination every 6 months through year 5, then annually thereafter. 1, 2

Structured Clinical Surveillance Schedule:

• Months 0-24: History and physical examination every 3 months 1, 2
• Years 3-5: History and physical examination every 6 months 1, 2
• Beyond 5 years: Annual history and physical examination with attention to secondary malignancies and late treatment effects 1, 2

Laboratory Monitoring:

• Blood counts: At 3,6,12, and 24 months, then only as clinically indicated 1, 2
• LDH levels: Same intervals as blood counts 2
• Years 3-5: Laboratory work only as clinically indicated for suspicious symptoms 2

Limited Role for CT Imaging:

• Minimal CT surveillance: May be performed at 6,12, and 24 months after treatment completion, though this is common practice rather than evidence-based 1
• Not mandatory: Regular CT scans are not mandatory outside clinical trials, especially if abdominal ultrasound is applicable 1

When PET Imaging IS Appropriate

PET scans should only be obtained in specific clinical scenarios:

• Suspected relapse: When clinical symptoms, physical examination findings, or laboratory abnormalities suggest disease recurrence 1, 2
• Equivocal CT findings: To characterize abnormal CT findings or detect recurrence within/around areas of radiation change 1
• Pre-biopsy planning: To identify metabolically active areas for tissue sampling 1

Critical requirement: If PET becomes positive during follow-up, biopsy confirmation is mandatory before changing treatment course 1, 3

Important Clinical Context

Patients with lymphoma who are event-free at 2 years have survival identical to the general population, emphasizing that intensive disease monitoring is most critical only in the first 2 years 1. Your patient at 1 year 9 months with a normal PET scan has an excellent prognosis, and the focus should shift toward:

• Detecting symptomatic relapse early: Patient-reported symptoms detect the majority of relapses 2
• Monitoring for late treatment effects: Thyroid dysfunction (if neck irradiation received), cardiovascular toxicity from anthracyclines, and secondary malignancies 2
• Avoiding unnecessary testing: That provides no survival benefit while exposing patients to radiation and false-positive results 1, 4

Treatment-Specific Long-Term Monitoring

Beyond lymphoma surveillance, ensure appropriate screening for late effects:

• Thyroid function testing: At 1,2, and 5 years if neck irradiation was received 1, 2
• Cardiovascular monitoring: For all patients who received anthracyclines or chest/mediastinal radiation 2
• Breast cancer screening: Annual screening for women over 35 who received radiation above the diaphragm 2

Common Pitfalls to Avoid

• Do not order routine surveillance PET scans in asymptomatic patients—this has no survival benefit and high false-positive rates 1, 2, 4
• Do not ignore patient-reported symptoms between scheduled visits—these detect most relapses more effectively than imaging 2
• Do not skip long-term follow-up beyond 5 years—the focus shifts to secondary malignancies rather than lymphoma relapse 1, 2
• Do not act on positive PET findings without biopsy confirmation—the positive predictive value is poor in surveillance settings 1, 3, 4