June 2021 – Bone and Soft Tissue Pathology Case 1

The correct answer is: Leiomyosarcoma.

Leiomyosarcomas are malignant neoplasms of smooth-muscle cells that typically occur from middle age to older individuals. While the most common site of origin is in the retroperitoneum, leiomyosarcomas often arise from blood vessels, as was seen in this case. A key histologic feature of leiomyosarcomas are intersecting fascicles of spindle cells with abundant eosinophilic cytoplasm. In addition, larger tumors typically demonstrate areas of coagulative tumor necrosis and hyalinized tissue. At the nuclear level, elongated, blunt-ended, cigar-shaped nuclei are readily identified. Nuclear atypia and mitosis are also appreciated with close examination. SMA and desmin stains are positive in most well-differentiated leiomyosarcomas; however, de-differentiated tumors demonstrate focal loss of both stains.  

Leiomyomas also demonstrate intersecting fascicles and blunt-ended cigar-shaped nuclei. Important histologic differences that can be used to differentiate leiomyomas from leiomyosarcomas is the lack of nuclear atypia, necrosis, or mitosis, all of which were observed in this case. The presence of any of these features should prompt careful further examination of the specimen, including additional levels, if possible. 

Lipomas are benign tumors of mature adipocytes. Grossly, the cut surface of lipomas appears homogenously yellow. Leiomyosarcomas demonstrate a white to tan cut surface and typically will have whorls. The histologic appearance of lipomas is that of mature adipocytes with eccentrically located nuclei.

Malignant peripheral nerve sheath tumors are neoplasms involving the peripheral nerve. These lesions can be sporadic but are often associated with disorder neurofibromatosis type 1. Imaging can be useful in identifying if the lesion is arising from or is associated with a peripheral nerve, unlike the vein, as was seen in this case. Microscopically malignant peripheral nerve sheath tumors demonstrate uniform spindle cells with areas of hyper and hypocellularity.  

References

1. The WHO Classification of Tumours Editorial Board. WHO Classification of Tumours Soft Tissue and Bone Tumours, 5th ed. Lyon: IARC Press; 2020.
   
2. Farshid G, Pradhan M, Goldblum J, Weiss SW. Leiomyosarcoma of somatic soft tissues: a tumor of vascular origin with multivariate analysis of outcome in 42 cases. Am J Surg Pathol. 2002 Jan;26(1):14-24. 
   
3. Muratori F, Greto D, Cenatiempo M, Mazzei G, Frenos F, Roselli G, Livi L, Capanna R, Baldi G, Campanacci DA. Leiomyosarcoma: Clinicopathological study and retrospective analysis of prognostic factors in a series of 100 patients. J Orthop. 2019 Mar 25;16(4):303-307. 
   
4. George S, Serrano C, Hensley ML, Ray-Coquard I. Soft Tissue and Uterine Leiomyosarcoma. J Clin Oncol. 2018 Jan 10;36(2):144-150.