Leopardlike PET Pattern and Sarcoidlike Reaction

A rare but often favorable immune-related adverse event associated with immune checkpoint inhibitors can mimic cancer progression on imaging and typically resolves with conservative management.

By
Kathryn Wighton
January 9, 2026
3 min

Conexiant

Objective:

To report a case of a drug-induced sarcoidosislike reaction (SLR) diagnosed through a distinctive PET pattern in a patient undergoing immune checkpoint inhibitor therapy.

Approach:

Key Findings:

SLRs are increasingly recognized immune-related adverse events that can mimic malignancy on imaging.
Approximately 4% of patients treated with immune checkpoint inhibitors may experience SLRs, often asymptomatic.
65% to 88% of patients with immune checkpoint inhibitor-associated SLR show tumor response or stable disease.

Interpretation:

SLRs, while rare, are associated with favorable outcomes and should be differentiated from true tumor progression through biopsy.

Limitations:

SLRs may be underreported as many patients are asymptomatic.
There are no standardized management guidelines for SLRs.

Conclusion:

Sarcoidlike reactions induced by immunotherapy are rare but generally have a favorable prognosis; biopsy is crucial for accurate diagnosis and management.