What happened, in summary

A 73-year-old woman had been diagnosed 5 years earlier with Stage I triple-positive cancer of the right breast. She underwent lumpectomy with sentinel lymph-node biopsy. The tumor was estrogen-receptor positive, progesterone-receptor positive, and HER2-positive. She then received paclitaxel with trastuzumab for 3 months, completed breast radiation, and continued trastuzumab for another 9 months.

Four years after the breast-cancer diagnosis, a CA 15-3 blood test was found to be markedly elevated. Because this raised concern for recurrence, she underwent breast imaging and broader scans. Mammography, ultrasound, and breast MRI showed only postsurgical changes, with no evidence of recurrent breast cancer. Instead, imaging found a large right-kidney mass.

She underwent radical nephrectomy, and pathology showed an oncocytic renal neoplasm rather than metastatic breast cancer. The kidney tumor stained for CA 15-3, and her blood level returned to normal 3 months after surgery. At 5 years from the breast-cancer diagnosis, there was no evidence of breast-cancer recurrence.