A case report of breast cancer recurrence with cystitis: the impact of immune checkpoint inhibitor therapy on the incidence of cystitis

BACKGROUND: Immune checkpoint inhibitors (ICIs) are essential for advanced breast cancer, particularly triple-negative breast cancer (TNBC) patients. While effective, they may cause immune-related adverse events (irAEs), including rare cases of cystitis with unclear mechanisms. This study reports a cystitis case following ICI therapy in a recurrent breast cancer patient, exploring potential associations. CASE PRESENTATION: A 51-year-old female with recurrent breast cancer (TNBC-like, IM subtype) following a 10-year disease-free interval underwent treatment with a paclitaxel-based chemotherapy regimen combined with camrelizumab. Three weeks after initiating ICI therapy, urinary frequency, urgency, dysuria, and hematuria developed. Urinalysis showed leukocyte esterase 3+, protein 2+, and occult blood 2+, with negative bacterial and fungal cultures. Bladder wall thickening and mild bilateral hydronephrosis were detected on ultrasound. Symptomatic management, including urinary alkalization and anti-inflammatory therapy, resulted in gradual symptom improvement. After discontinuation of camrelizumab, the patient experienced two episodes of cystitis, both of which resolved following treatment with methylprednisolone, with no further episodes observed during subsequent follow-up. CONCLUSION: This case highlights a rare presentation of immune-related cystitis associated with ICI therapy in recurrent breast cancer. ICIs may increase cystitis risk through immune-mediated mechanisms, although the underlying pathophysiology remains unclear, warranting further investigation.