Breast cancer is the most frequent non-skin cancer in women and bone is its most common site of metastasis. The patella, as the largest sesamoid bone in the human body, is a rare site for cancer metastasis to occur. We reported the comprehensive auxiliary examination data and complete process of diagnosis, management and follow-up for a case of solitary patellar metastasis from breast cancer.
A 47-year-old woman presented with patellar pain 6 years after breast cancer surgery. Thorough imaging and pathology examinations were carried out leading to a diagnosis of breast-derived patellar metastasis. Subsequent treatment and follow-up were performed. The patient recovered function slightly at 3 months postoperatively, but tibia and femur metastases developed at 6 months postoperatively and the patient started radiotherapy.
Cases of patellar metastases from malignant tumors are extremely rare but do exist. Due to the insidious onset and non-specific symptoms, it is worthwhile to alert clinicians. The diagnostic value of positron emission tomography/computed tomography for patellar metastases is significant and still provides certain advantages compared to pathologic examination, so it can be given priority. Prompt postoperative radiotherapy is necessary, while imaging should be actively performed with a short review interval.

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