Incidental Detection of a CAIX-avid Breast Invasive Ductal Carcinoma on 68Ga-NY104 PET/CT During Evaluation of a Suspected Renal Mass

68Ga-NY104 is a novel tracer targeting carbonic anhydrase IX (CAIX) with promising diagnostic efficacy for clear cell renal cell cancer. We present a 55-year-old woman with a suspected left renal mass who underwent 68Ga-NY104, showing no significant uptake in the renal mass but incidentally revealing an intense uptake nodule in the left breast. Subsequent 18F-FDG PET/CT revealed mild renal mass and intense breast nodule uptake. Postoperative pathology confirmed the renal mass as benign angiomyolipoma and the breast nodule as invasive ductal carcinoma. This case highlights the inclusion of primary breast cancer in the differential diagnosis of extra-renal CAIX-avid lesions.