Opportunistic bowel infection after corticosteroid dosage tapering in a stage IV lung cancer patient with tislelizumab-related colitis.

Immune checkpoint inhibitors, the new standard in cancer therapy, present durable responses in numerous solid tumors and hematologic malignancies, as well as resulting in an increased incidence of immune-related adverse events (irAEs). Diarrhea is a common irAE, with an incidence rate of approximately 10% to 13%. It is important to distinguish between diarrhea symptomatic of an infection, which is the main differential diagnosis, and immune-related diarrhea. Here, we report a case of an advanced lung cancer patient who presented with diarrhea as a result of treatment with tislelizumab, a novel PD-1 inhibitor. Although the patient initially responded to corticosteroid treatment, diarrhea recurred upon dosage tapering, and eventually improved on treatment with ganciclovir and vancomycin. Therefore, clinicians must remain highly vigilant against infection and carefully distinguish symptoms of infection from irAEs by performing repeated blood or fecal examinations for pathogens, colonoscopy, and biopsy.