Eosinophilic fasciitis in a patient treated by atezolizumab for metastatic triple-negative breast cancer

Immune checkpoint inhibition has revolutionized the treatment for numerous cancer patients; however, the spectrum of immune-related adverse events (irAEs) remains to be fully uncovered. We report a 48-year-old woman who was treated in the Phase III IMpassion130 study (atezolizumab and nanoparticle albumin-bound [nab]-paclitaxel) for metastatic triple-negative breast cancer. She experienced a partial response after 3 months. Nevertheless, the patient presented with thickening of the skin and muscle fatigue in the distal extremities together with blood eosinophilia after 15 months. Skin biopsy and magnetic resonance imaging were diagnostic of eosinophilic fasciitis (EF). Symptoms clearly improved upon stopping atezolizumab, while tumor response is still ongoing after discontinuing treatment. We identified five other cases of EF during immunotherapy, all occurring after about 1 year and in contrast to our case, mostly accompanied by other irAEs. This highlights that even if EF is a rare irAE, timely recognition and management remains important.