A case of eosinophilic cystitis coexisting of superficial bladder cancer, mimicking muscle‐invasive cancer

Introduction Here, we present a rare case of eosinophilic cystitis coexisting with bladder cancer, which appeared to be an invasive carcinoma on imaging. Case presentation A 46‐year‐old man presented with urinary urgency. Computed tomography revealed an irregular and thickly enhanced bladder wall, which seemed to be invasive bladder cancer. Cystoscopy revealed a raspberry‐like mass lesion on the entire bladder circumference. Pathological diagnosis after transurethral resection was pathological T1 urothelial carcinoma. After a thorough discussion of treatment options, the patient elected to receive intravesical Bacillus Calmette‐Guérin. Three months after Bacillus Calmette‐Guérin administration, no residual disease was confirmed by transurethral biopsy, and no recurrence was observed over 2 years. As peripheral eosinophilia and submucosa eosinophil infiltration were identified, the patient was diagnosed with coexisting eosinophilic cystitis and urothelial carcinoma. Conclusion Clinicians should consider the possibility of eosinophilic cystitis with superficial bladder cancer coexistence in patients who present with an irregular and thick bladder wall.