Patterns of bone morphogenetic protein-2 expression in smooth muscle tumors of the uterine corpus and other uterine tissues.

Bone morphogenetic proteins (BMPs) are extracellular, multifunctional growth factors that constitute the largest subset of the transforming growth factor β superfamily. BMP2 is involved in cardiovascular embryogenesis, in addition to a variety of other postnatal functions, such as neovascularization, osteoinduction, tumor signaling, and in the uterus, stromal decidualization at the implantation site. Estrogen receptor signaling is common in smooth muscle tumors of the uterus, and preclinical models suggest significant interactions between BMP2 and estrogen receptor-mediated signaling. The purpose of this study is to define the patterns of BMP2 expression, as assessed by immunohistochemistry, in smooth muscle tumors and other tissues of the uterine corpus, and to establish whether BMP2 expression has any prognostic significance in uterine leiomyosarcomas. BMP2 was positive (cytoplasmic pattern, typically focal) in 24% of leiomyosarcomas and 20.7% of leiomyomata, but was either infrequently expressed or not expressed in all other tissues evaluated, including normal myometrium and endometrium, endometrial stromal tumors, typical adenomyoma, adenomyosis, and serosal endometriosis. The endothelial cells of small, thin-walled vessels were frequently, but not invariably immunoreactive for BMP2. There was no significant difference between BMP2⁺ and BMP⁻ leiomyosarcomas regarding average tumor size, average patient age, microvessel density, and proportions with high tumor grade, advanced stage and frequency of death from disease on follow-up. Two (29%) of 7 BMP2⁺ leiomyosarcomas were estrogen receptor+, compared with 5 (50%) of 10 BMP2⁻ leiomyosarcomas, a statistically insignificant difference (P=0.62). It is concluded that BMP2 is only expressed in a minority of smooth muscle tumors of the uterine corpus, and lacks prognostic significance in leiomyosarcomas. BMP2 is rarely expressed in the other nonendothelial tissues of the human uterine corpus that were evaluated. The significance of frequent BMP2 expression in small vessels of the uterus requires further investigation.