KIT expression in angiosarcomas and fetal endothelial calls: Lack of mutations of exon 11 and exon 17 of c-kit

C-kit proto-oncogene product (KIT, CD117) is a tyrosine kinase growth facto r receptor for stem cell factor. This receptor is important for the develop ment and maintenance of hematopoietic stem cells, mast cells, germ cells, m elanocytes, and interstitial cells of Cajal and is constitutively expressed in them. Among mesenchymal tumors, KIT seems to he specific for the gastro intestinal stromal tumors, which consistently express this protein. Activat ing mutations in the tyrosine kinase or juxtamembrane domains of c-kit gene have been found in mastocytoma, seminoma, and gastrointestinal stromal tum ors. Following up our initial observation of KIT expression in one angiosar coma, we examined 50 angiosarcomas, 13 Kaposi sarcomas, 10 epithelioid hema ngioendotheliomas, and 31 hemangiomas of different types for KIT expression using a polyclonal antiserum specific to KIT. Adult and fetal tissues and neovascular endothelia in 20 carcinomas were studied for comparison. More t han half (56%) of the angiosarcomas representing different clinicopathologi c and histologic subtypes and 2 of 13 Kaposi sarcoma were KIT positive. All epithelioid hemangioendotheliomas and hemangiomas were negative, with the exception of two infantile hemangiomas that showed KIT reactivity. The feta l capillary endothelia of lungs, placenta, and soft tissues were also KIT p ositive, although in soft tissues and placenta, KIT positivity was more pro minent in the first trimester, However, endothelia of adult vessels and neo vascular capillaries of carcinomas were negative. None of the four KIT-posi tive angiosarcomas and one KIT-positive Kaposi sarcomas that were studied s howed mutations in the juxtamembrane or tyrosine kinase domains of the c-ki f gene. These results indicate that KIT expression occurs in a subset of an giosarcomas, and the expression probably represents oncofetal expression (i .e., reversion of the tumor cell phenotype to that of fetal endothelial cel ls that may show KIT expression).