Leiomyosarcoma | Dermatopathology

The findings are diagnostic of a well differentiated atypical leiomyomatous tumor. Based on the extent of cytologic atypia, mitotic activity and Ki-67 proliferation index this lesion is best treated and categorized as a leiomyosarcoma. This would be a probable superficial variant of presumptive origin from the pilar arrector muscle. Some authors have argued that these lesions should perhaps be designated as atypical leiomatous tumors since their biological course is one associated only with local disease without metastatic potential. It is well known that these lesions do have a cognate morphology to their benign counterparts however it is the pleomorphism and mitotic activity that would separate this lesion from a leiomyoma. The differential diagnosis would encompass a symplastic leiomyoma however the overall degree of cellularity and mitotic activity would not support this particular designation.

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Slide 1: 460 year-old man with a chest nodule. The biopsy shows a spindle cell proliferation that is of moderate to high cellularity assuming an intersecting vesicular growth pattern within the dermis. There is a Grenz zone that separates the proliferation from the overlying epidermis.

Slide 2: Under higher magnification the nuclei are elongate with predominantly blunt ended nuclei albeit a few of the cells have a more tapered appearance. The chromatin is finely dispersed in many of the cells with inconspicuous nucleoli recognizing however that there are a number of cells which are strikingly hyperchromatic with nuclear enlargement and nuclear contour irregularity.

Slide 3: The elongate nuclei have irregular borders with pseudo-nuclear inclusions. Mitotic figures are not infrequent. The mitotic figures identified are atypical. The mitotic rate is 3/mm2.

Slide 4: The neoplastic cells are desmin positive. There is also marked staining for actin (not shown). The S-100 and Melan-A preparations are negative. The proliferation index is abnormal. In areas of fairly striking cellular atypia the Ki-67 proliferation index is high (not shown).