Based on the patients history (unexplained weight loss) and bone scan, she has an aggressive lesion in her pelvis. Immunohistochemisty staining for smooth muscle actin suggests a tumor of smooth muscle origin - or a leiomyosarcoma. The prefix - "leio-" designates smooth muscle tumors. The histopathology presented in Figure A shows interlacing bundles of smooth muscle cells with variable uniformity, high nuclear/cytoplasmic ratio, and mitotic figures - consistent with leiomyosarcoma. The other histopathology slides are: Figure B - Giant cell tumor, Figure C - Myeloma, Figure D - Osteosarcoma, Figure E - hyaline cartilage. The two cited review articles by Berlin et al and Antonescu et al describe the clinical, radiographic, and histology of this disease as described above.
Berlin O, Angervall L, Kindblom LG, Berlin IC, Stener B. Primary leiomyosarcoma of bone. A clinical, radiographic, pathologic-anatomic, and prognostic study of 16 cases. Skeletal Radiol. 1987;16(5):364-76. Review.
PMID:3306938 (Link to Abstract)
Antonescu CR, Erlandson RA, Huvos AG. Primary leiomyosarcoma of bone: a clinicopathologic, immunohistochemical, and ultrastructural study of 33 patients and a literature review. Am J Surg Pathol. 1997 Nov;21(11):1281-94. Review.
PMID:9351566 (Link to Abstract)