A Rare Case Report of Primary Leiomyosarcoma of Distal Femur Bone in a Patient with Multiple Myeloma and Review of Literature

Abstract

Primary leiomyosarcoma of bone is rare, with < 0.7% incidence of all primary malignant bone tumors. Here we report a primary leiomyosarcoma of bone arising in a patient with multiple myeloma. The patient is a 72-year-old male who was initially diagnosed with multiple myeloma (IgG Kappa) in 2007 which presented as a large plasmacytoma involving his thoracic vertebrae. He was treated with chemotherapy and eventually had a stem cell transplant in 2015. In 2017, a routine skeletal survey demonstrated a solitary lytic lesion in the right distal femur. The lesion grew fast and doubled in size to 7.9 cm within one year. The lesion was biopsied and proven to be a leiomyosarcoma. A total body PET/CT scan showed no evidence of other primary tumors or metastatic disease. The patient then underwent a distal femur resection. Grossly, majority of the tumor involved distal femur cortical bone and medullary cavity with focal extension into the surrounding soft tissue. Microscopically, the tumor consisted of fascicles of spindle cells with a focal storiform growth pattern. The tumor cells had eosinophilic cytoplasm and focally pleomorphic nuclei.  The tumor cells were positive for SMA and Calponin and negative for Desmin, Myo-D1, Myogenin and S-100 immunohistochemical stains. The morphology and immunoprofile favored a diagnosis of pleomorphic leiomyosarcoma. Primary leiomyosarcoma of bone is a rare tumor and this patient’s history of multiple myeloma made it even more challenging to make an early clinical diagnosis.

[N A J Med Sci. 2020;1(1):024-027.   DOI:  10.7156/najms.2020.1301024]

Key Words: primary leiomyosarcoma, femur, multiple myeloma