Bladder metastasis arising from right: sided invasive lobular carcinoma in bilateral synchronous discordant primary breast cancers-a rare case.

Bladder metastasis of breast cancer is clinically rare, and there is no report on simultaneous bilateral breast cancer with different pathological types complicated by bladder metastasis. This study reports a case of bladder metastasis in a patient with simultaneous bilateral breast cancer of different pathological types. The patient is a 71-year-old woman who was diagnosed with simultaneous bilateral breast cancer six years ago (invasive lobular carcinoma in the right breast and invasive carcinoma of no special type in the left breast). She received adjuvant radiotherapy, chemotherapy, and endocrine therapy after surgery. Four years ago, she developed vertebral metastasis. In January 2022, she presented with intermittent gross hematuria. Imaging studies showed diffuse thickening and enhancement of the bladder wall with surrounding infiltration on CT and hydronephrosis on ultrasound. Biopsy confirmed metastasis of invasive lobular carcinoma of the breast. The patient was diagnosed with stage IV Her2-positive breast cancer with bone and bladder metastasis. This paper aims to explore its diagnostic features, treatment strategies, and prognostic factors.