A distinctive “leopardlike” pattern of hypermetabolic muscle lesions on positron emission tomography/computed tomography (PET/CT) led to the diagnosis of a drug-induced sarcoidosislike reaction (SLR)—not cancer progression—in a patient receiving immune checkpoint inhibitor therapy, according to a case published in JAMA Oncology.
The diagnosis has important clinical implications because SLRs, while uncommon, are increasingly recognized immune-related adverse events that can closely resemble malignancy on imaging but are usually associated with tumor control and favorable outcomes.
The patient, a 52-year-old woman with a history of multiple squamous cell carcinomas, developed progressive unilateral lower limb edema and painful inflammatory ulcerations after 9 months of adjuvant durvalumab therapy. FDG-PET/CT revealed multiple hypermetabolic lesions in the lower limb muscles forming a striking leopardlike pattern, along with hypermetabolic lymphadenopathy above and below the diaphragm—findings initially concerning for tumor progression, vasculitis, or inflammatory myopathy.
Muscle and skin biopsies instead demonstrated non-necrotizing epithelioid and giant cell granulomatous inflammation without vascular involvement or identifiable pathogens, confirming an immune checkpoint inhibitor–induced sarcoidosislike reaction.
Sarcoidosislike reactions are systemic granulomatous responses that are clinically and histologically indistinguishable from sarcoidosis. Although considered rare, their prevalence among patients treated with immune checkpoint inhibitors is estimated at about 4%, and may be underestimated because up to half of affected patients are asymptomatic. In published series, 65% to 88% of patients with immune checkpoint inhibitor–associated SLR experience objective tumor response or recognition of stable disease rather than progression.
There are no standardized management guidelines, but outcomes are generally favorable. Across studies, more than 90% of lesions improve or resolve regardless of whether corticosteroids are used or immunotherapy is discontinued. In the current case, durvalumab was stopped and the patient was managed conservatively with local wound care alone. Both clinical symptoms and imaging abnormalities resolved completely within 3 months, without systemic corticosteroid therapy.
“Sarcoidlike reactions induced by immunotherapy are rare but associated with a usually favorable prognosis,” the researchers wrote, emphasizing the importance of biopsy to distinguish these reactions from true tumor progression and guide appropriate management.
The case was reported by Guillaume Brenac, MD, of the Department of Internal Medicine and Clinical Immunology at Université Bourgogne Europe and CHU Dijon in France, and colleagues.
Full disclosures were reported by the authors in the case report.
Source: JAMA Oncology
