71-year-old Ms. S discovered a breast mass through imaging, with irregular margins, but a definite diagnosis could not be made by imaging alone. Blood tests revealed 106 circulating tumor cells (CTCs), indicating a very high risk of malignancy. Ms. S immediately decided to undergo surgery, and the pathological diagnosis was stage II breast cancer. Three weeks after surgery, blood tests were repeated to detect minimal residual disease (MRD), and the number of CTCs dropped to 11, suggesting a good surgical outcome.