A 64-year-old woman went to our ultrasound department with a lesion on the right side of the clavicle to the armpit subcutaneously. Her right upper arm was edema and accompanied by pain, numbness and discomfort in the right finger. The patient was diagnosed with right breast cancer 6 years before. Her primary lesion was invasive breast cancer (T2N1M0), immunohistochemistry showed ER (+), PR (+), HER-2 (+++). At that time she had right radical mastectomy and accepted both chemotherapy and radiotherapy. There is no history of past illness. There is no personal and family history. Scars were seen in the right chest area. The arm circumference was significantly widened. The upper part of the right forearm near to the proximal elbow was edema, with greater tension, accompanied by pain, numbness and discomfort at the end of the fingers. There was no difference in the remaining limbs, and the pathological signs were not elicited. Blood test showed an elevated tumor marker-cytokeratin (CK) (195.1 ng/mL). Ultrasound found a soft lesion measuring 38 mm × 37 mm which located on the right side of the clavicle to the armpit subcutaneously. Then series of other imaging and blood tests were done. MRI brachial plexus scan showed that the right side of brachial plexus was enlarged compared with the left side and brachial plexus bundle in the distance showed a flake shadow. FDG-PET/CT revealed that the right side of brachial plexus nodular appearance with increased FDG metabolism, an SUVmax of 13.7. Ultrasound exam also found many lesions between pectoralis major, deltoid muscle and inner upper arm.