Cluster Analysis of Immunohistochemical Markers in Leiomyosarcoma Delineates Specific Anatomic and Gender Subgroups

BACKGROUND: Leiomyosarcoma (LMS) can be categorized into uterine, retroperitoneal, nonretroperito-neal soft tissue, cutaneous, visceral, and osseous anatomic subtypes. The differential expression of smooth muscle markers, estrogen receptor (ER), progesterone receptor (PR), and Wilms tumor-1 protein (WT1) by anatomic subtype and gender was explored. METHODS: A total of 78 LMS comprised of 30 uterine and 48 nonuterine tumors were studied. Nonuterine tumors were comprised of 17 soft tissue, 16 retroperitoneal, 7 cutaneous, 5 visceral, and 3 osseous subtypes. Immunohistochemical staining intensity on tissue microarray slides was scored as 0, 1þ, or 2þ, and cluster analysis was performed on the data. RESULTS: Smooth mus-cle actin was the most sensitive antibody (95%), followed by muscle-specific actin (91%), calponin (88%), desmin (73%), caldesmon (66%), and myosin (64%). Caldesmon and myosin were usually coexpressed, and were highest in retroperitoneal tumors (94%). There was no discernable correlation noted between histo-logic differentiation and smooth muscle marker expression. ER was much more common in women, with the highest frequencies noted in female retroperitoneal (86%) and uterine (63%) tumors. Nuclear WT1 was expressed in 11 % of all tumors, and was limited to ER-positive uterine and female retroperitoneal tumors. Cluster analysis segregated 4 groups, most notably 1 driven by ER and PR, with the vast majority being uterine and female retroperitoneal tumors. CONCLUSIONS: Smooth muscle markers demonstrated variable sensitivities in LMS, with a tendency for anatomic subtypes to segregate based on expression patterns of these markers. ER defined a subgroup of uterine and female retroperitoneal tumors, and WT1 was limited to such tumors, suggesting a common line of differentiation as well as potential therapeutic targets. Cancer 2009;115:4186–95. VC 2009 American Cancer Society. KEY WORDS: leiomyosarcoma, immunohistochemistry, microarrays, cluster analysis, smooth muscle