Skeletal Muscle Metastases from Breast Cancer: Two Case Reports
A 52-year-old woman visited our hospital with a palpable left neck mass in April 2010. Her medical history showed that she had been diagnosed with left breast cancer (cT2N0M0) in December 2004, and she underwent modified radical mastectomy of the left breast in our hospital. An histopathological examination showed invasive ductal carcinoma with nuclear grade 2, and the absence of axillary lymph node metastases. Immunohistochemistry studies showed positive staining for ER and PR and negative staining for HER2 (score 0). She received five cycles of adjuvant CMF chemotherapy followed by tamoxifen (20 mg daily) for 2 years. She then on her own authority stopped taking tamoxifen and ceased regular surveillance.\nWe performed CT scans of the neck and breast, bone scan, and PET/CT. CT scans showed multiple enlarged lymph nodes in the left axillary region and the left lower cervical chain, and PET/CT showed multiple conglomerated enlarged lymph nodes with high FDG uptake (SUVmax, 7.02) in the left axillary, retropectoral, subclavian, internal mammary, and cervical lymph nodes. There were no metastatic sites except the lymph nodes. A core needle biopsy of the left axillary lymph node was performed, and pathological examination revealed metastatic adenocarcinoma, which was positive for ER, negative for PR, and equivocal for HER2 (score 2). She was postmenopausal based on the serum follicle-stimulating hormone level, and she started receiving the nonsteroidal aromatase inhibitor letrozole in May 2010. She also received radiotherapy to her left chest wall and regional lymphatics including the cervical chain (total dose, 5,040 cGy) between August 18 and September 30, 2010. Follow-up CT scans showed a complete regression of the previously invaded lymph nodes in November 2010.\nAbout 10 months later, she complained of a mild throbbing pain in the right buttock area that was aggravated by walking. On physical examination, there was no palpable mass and tenderness in the buttock area. CT scans of the abdomen-pelvis and PET/CT were performed in August 2011. Abdomen and pelvis CT scans showed no notable findings, but PET/CT showed multiple new enlarged lymph nodes with increased FDG uptake (SUVmax, 15.4) in the right iliac chain and a nodular lesion of about 2.5 cm in diameter (SUVmax, 20.1) in the right gluteus maximus muscle. We decided to switch from letrozole to the steroidal aromatase inhibitor exemestane on disease progression. Three months later, a follow-up abdominal CT scan showed no discernible change, so the patient continued to take exemestane. After 6 months of taking exemestane, PET/CT showed an increase in size of the right gluteal muscle mass and right iliac lymph nodes (). There was no evidence of local recurrence or other distant metastases. Based on PET/CT images, a poorly defined, mildly enhanced mass of 3 cm in diameter was identified in the right gluteus maximus muscle upon abdominal CT scan (). Therefore, we performed ultrasound-guided core needle biopsy of this gluteal muscle mass in February 2012. Pathological examination revealed invasive ductal carcinoma (), which was negative for ER and PR, and equivocal for HER2 (score 2). HER2 gene amplification was not observed by fluorescence in situ hybridization (HER2/CEP17 ratio, 1.26). Thus, expression of ER showed discordance between the primary breast cancer and the metastatic carcinoma. The patient received palliative chemotherapy with docetaxel and epirubicin. After two cycles of chemotherapy, a follow-up abdominal CT scan showed partial regression of the gluteal muscle mass and iliac lymph nodes, with a decrease in diameter of the gluteal muscle mass from 3.0 to 2.1 cm. She continued to receive chemotherapy and follow-up.