KIT Expression in Angiosarcomas and Fetal Endothelial Cells: Lack of Mutations of Exon 11 and Exon 17 of C-kit Markku Miettinen, M.D., Maarit Sarlomo-Rikala, M.D., Jerzy Lasota, M.D. Department of Soft Tissue Pathology, Armed Forces Institute of Pathology (MM, JL), Washington, D.C., and Department of Pathology, Haartman Institute of the University of Helsinki (MS-R), Helsinki, Finland results indicate that KIT expression occurs in a sub- C-kit proto-oncogene product (KIT, CD117) is a ty- set of angiosarcomas, and the expression probably rosine kinase growth factor receptor for stem cell represents oncofetal expression (i.e., reversion of factor. This receptor is important for the develop- the tumor cell phenotype to that of fetal endothelial ment and maintenance of hematopoietic stem cells, cells that may show KIT expression). mast cells, germ cells, melanocytes, and interstitial cells of Cajal and is constitutively expressed in KEY WORDS: Genetics, KIT, Vascular tumors. them. Among mesenchymal tumors, KIT seems to Mod Pathol 2000;13(5):536–541 be specific for the gastrointestinal stromal tumors, which consistently express this protein. Activating C-kit gene encodes for a tyrosine kinase growth mutations in the tyrosine kinase or juxtamembrane factor receptor for stem cell factor (also called mast domains of c-kit gene have been found in mastocy- cell growth factor). KIT protein (CD117 in the stan- toma, seminoma, and gastrointestinal stromal tu- dardized terminology of leukocyte antigens) is con- mors. Following up our initial observation of KIT stitutionally expressed in hematopoietic stem cells, expression in one angiosarcoma, we examined 50 mast cells, germ cells, melanocytes, certain basal angiosarcomas, 13 Kaposi sarcomas, 10 epithelioid epithelial cells, luminal epithelium of breast, and hemangioendotheliomas, and 31 hemangiomas of the interstitial cells of Cajal of the gastrointestinal different types for KIT expression using a polyclonal tract. KIT protein is important for the development antiserum specific to KIT. Adult and fetal tissues and maintenance of these cell types (1–6). and neovascular endothelia in 20 carcinomas were Among mesenchymal tumors, KIT is consistently studied for comparison. More than half (56%) of the expressed in the gastrointestinal stromal tumors angiosarcomas representing different clinicopatho- (GISTs), the major subset of the mesenchymal tu- logic and histologic subtypes and 2 of 13 Kaposi mors of the gastrointestinal tract, many of which sarcoma were KIT positive. All epithelioid heman- also express another antigen of hematopoietic pro- gioendotheliomas and hemangiomas were negative, genitor cells, CD34 (7–10). In a previous study, KIT with the exception of two infantile hemangiomas was not found in other CD34-positive tumors, such that showed KIT reactivity. The fetal capillary endo- as solitary fibrous tumor and Kaposi sarcoma (KS), thelia of lungs, placenta, and soft tissues were also and was only sporadically encountered in dermat- KIT positive, although in soft tissues and placenta, ofibrosarcoma protuberans and hemangiopericy- KIT positivity was more prominent in the first tri- toma (9). mester. However, endothelia of adult vessels and Gain-of-function mutations in c-kit gene have neovascular capillaries of carcinomas were nega- been shown in mastocytosis (11–13), GIST (7, 14– tive. None of the four KIT-positive angiosarcomas 18), and more recently in seminoma (19). In mas- and one KIT-positive Kaposi sarcomas that were tocytosis and seminoma, different point mutations studied showed mutations in the juxtamembrane or have been found in the tyrosine kinase domain tyrosine kinase domains of the c-kit gene. These (exon 17) at the same nucleotide (2467) position. In GISTs, the mutations involved the juxtamembrane Copyright © 2000 by The United States and Canadian Academy of domain, exon 11 of the c-kit gene. Most common, Pathology, Inc. the mutations in GISTs are in frame deletions of VOL. 13, NO. 5, P. 536, 2000 Printed in the U.S.A. Date of acceptance: November 22, 1999. several codons or, less common, in point mutations The opinions and assertions contained herein are the expressed views of the authors and are not to be construed as official or reflecting the views and insertions (7, 14–18). of the Departments of the Army or Defense. Following up our initial immunohistochemical Address reprint requests to: Markku Miettinen, M.D., Department of Soft Tissue Pathology, Armed Forces Institute of Pathology, 14th Street and observation of KIT expression in one angiosarcoma, Alaska Avenue, N.W., Washington, DC 20306-6000; fax: 202-782-9182. we analyzed 104 vascular tumors and fetal and 536 adult endothelial cells for KIT expression. Some Molecular Studies of c-kit Gene fetal blood vessels and more than half of the angio- DNA for the polymerase chain reaction (PCR) sarcomas showed KIT expression, but normal adult amplification was obtained from formalin-fixed endothelia were negative. However, no mutations and paraffin-embedded tissues, and the quality of were found in exon 11 and exon 17 of c-kit gene. DNA templates was verified by amplification of two Therefore, KIT expression in angiosarcoma proba- fragments of genomic DNA (133 bp and 268 bp) as bly represents an oncofetal expression paralleling previously reported (16). The entire exon 11 of c-kit the KIT expression of developing endothelia. gene was PCR amplified for 40 cycles with forward primer CK10.4 (16) and the reverse primer CK11.3 (5Ј-AGC CCC TGT TTC ATA CTG AC-3Ј). The PCR MATERIALS AND METHODS assay yielded amplification products of 250 bp. In one case with unoptimally preserved DNA, a semi- Tissues nested PCR was performed to amplify exon 11 of ␮ KIT expression was studied in 50 angiosarcomas, c-kit. Aliquot of the PCR products (0.1 l) from the 13 KS, 10 epithelioid hemangioendotheliomas, and CK10.4/CK11.3 reaction was reamplified (30 cycles) 31 hemangiomas, including 6 infantile capillary using forward CK10.4 and reverse CK11.2 primers hemangiomas obtained from the Soft Tissue Regis- (16). The semi-nested PCR assay yielded amplifica- try from the Armed Forces Institute of Pathology. tion products of 192 bp. The annealing temperature The diagnosis of angiosarcoma was based on dis- was 56° C for both assays. The region of exon 17 of tinctive vasoformation by the tumor cells or by c-kit with previously reported mutation at the po- demonstration of CD31 in all cases included in this sition 2467 was PCR amplified for 30 cycles using Ј study. Histologically normal fetal tissues from first forward primer CK17.1 (5 -TCC TTA CTC ATG GTC Ј Ј (n ϭ 4), second (n ϭ 7), and third trimesters (n ϭ 3) GGA TC-3 ) and reverse primer CK17.2 (5 -CAG Ј were studied for comparison. In addition, KIT ex- GAC TGT CAA GCA GAG AA-3 ). The annealing pression was studied in normal adult tissues from temperature was 50° C. The PCR reaction condi- brain, skin, breast, subcutaneous soft tissues, skel- tions in all assays were the standard ones recom- etal muscle, tonsil, trachea, lung, liver, appendix, mended by Perkin Elmer (Norwalk, CT). The PCR small intestine, colon, kidney, endometrium, myo- products were size-fractionated on 2% and 3.5% metrium, fallopian tube, and ovary. Twenty KIT- agarose gels, purified from the gels (Qiagene, Inc., negative carcinomas with tumor neovasculariza- Chatsworth, CA) and sequenced directly on a 373 tion were also studied, including 5 renal DNA sequencer (Applied Biosystems, Foster City, carcinomas, 5 ovarian high-grade carcinomas, 5 co- CA). Computer analysis of the DNA sequences were lonic adenocarcinomas, and 5 Merkel cell carcino- performed using Lasergene software (DNASTAR, mas. Madison, WI) in connection with the data of the GeneBank 110/EMBL57 database. To prevent PCR contamination, standard precautions were under- taken, including multiple negative controls in each Immunohistochemistry experiment to monitor the possible contamination. The normal tissues, carcinomas, and vascular tu- mors were immunohistochemically evaluated for the KIT protein. A polyclonal antibody was used RESULTS (sc-168; Santa Cruz Biotechnology, Santa Cruz, CA; diluted at 1:400). In control tissues, this antibody KIT (CD117) Expression in Embryonic But Not in reproduced the known patterns of KIT specificity Adult and Neovascular Endothelial Cells with expression in ovocytes, fetal testicular germ A 6- to 7-week embryo showed KIT reactivity in cells, mast cells, terminal ductal epithelia of breast, capillaries of the placental villi (Fig. 1A) and the melanocytes, and Cajal cells of the gastrointestinal primitive mesenchyme (Fig. 1B). Villous tropho- tract. The immunohistochemical studies were per- blast also showed KIT positivity that was weaker formed by the avidin-biotin complex method (Vec- than that seen in the endothelial cells (Fig. 1A). tastain Elite; Vector Labs, Burlingame, CA) or by KIT-positive capillary endothelia were also seen in Ventana automated immunostainer (Ventana Med- the endocardium and the chorioallantoic sac of the ical Systems, Tucson, AZ, with their detection sys- 6- to 7-week embryo. The capillary endothelial tems); equal results were documented in control cells, along with scattered hematopoietic cells and stains. Diaminobenzidine added with hydrogen portions of the developing spinal cord, were the peroxide was used as the chromogen. Appropriate only KIT-positive cells identified in the early em- negative controls (omission of primary antibody) bryo. Three other first trimester embryos/fetuses and positive controls (a multitissue block with 33 also showed KIT positivity in some but not all cap- normal tissues) were evaluated in each run. illaries of soft tissues. Alveolar capillaries of lungs KIT in Angiosarcoma (M. Miettinen et al.) 537 FIGURE 1. KIT expression in fetal endothelial cells and angiosarcomas (A, B, and C, immunoperoxidase, 480ϫ). A, the capillary endothelial cells of the placental villi of a 6- to 7-week embryo are KIT positive. Note also KIT positivity of the trophoblast. B, the primitive mesenchyme of a 6- to 7- week embryo shows delicate KIT-positive capillaries.