Co-occurrence of breast cancer and malignant peripheral nerve sheath tumor in a patient with neurofibromatosis type 1.

Patients with neurofibromatosis type 1 (NF1) have an increased risk of developing breast cancer and other malignancies. During the search for breast cancer metastases in NF1 patients, there is a substantial probability of detecting malignancies other than breast cancer. We present a case of an 80-year-old woman with NF1 who was diagnosed with both invasive ductal carcinoma of the luminal-HER2 type in the breast and a malignant peripheral nerve sheath tumor (MPNST) of the liver. After noticing a lump in her right breast for 2 months, further examination confirmed breast cancer with metastases to the right axillary lymph nodes. A whole-body contrast-enhanced CT scan revealed large hepatic tumors initially suspected to be metastases from breast cancer. However, given the patient's underlying NF1, an ultrasound-guided liver biopsy was performed, which confirmed the diagnosis of MPNST. The patient had a history of surgical resection for the MPNST in the forearm. Due to the high metastatic potential of MPNST, the liver tumors were diagnosed as metastases of the MPNST. She declined chemotherapy for MPNST and is currently receiving endocrine therapy alone for breast cancer. It is necessary to acknowledge the predisposition of patients with NF1 to develop various tumors throughout the body. When performing a systemic evaluation for breast cancer in NF1 patients, any detected lesions should be thoroughly investigated for potential malignancies other than breast cancer metastasis. Biopsy and pathological examinations are useful to ensure an accurate differential diagnosis.