INFLAMMATORY MYOFIBROBLASTIC TUMOR - CYTOGENETIC EVIDENCE SUPPORTING CLONAL ORIGIN

The inflammatory myofibroblastic tumor (IMT) is a distinctive but cont roversial lesion, usually occurring during childhood, composed of fasc icles of bland myofibroblastic cells admixed with a prominent inflamma tory infiltrate consisting of lymphocytes, plasma cells, and eosinophi ls. Often affecting the lung and associated with constitutional sympto ms, this lesion has been variously terms plasma cell granuloma, inflam matory pseudotumor, inflammatory myofibrohistiocytic proliferation, an d inflammatory fibrosarcoma to reflect divergent views concerning its pathogenesis and level of malignancy Cytogenetic analysis of an intra- abdominal myxoid hamartoma, a probable variant of this lesion, and a p ulmonary IMT demonstrated clonal chromosomal abnormalities, lending su pport to the view that the IMT might be a neoplasm. There have been fe w cases studied to date, however, and the extent of cytogenetic anomal ies in IMTs is not known. Karyotype analyses were performed on IMTs sh owing typical histologic features from three children. In addition, on e case was studied by fluorescence in situ hybridization. Seventeen of 20 metaphase cells examined from a pulmonary IMT in a 5.5-year-old gi rl had an abnormal 47,XX + r(ring) karyotype. Fluorescence in situ hyb ridization studies demonstrated that the ring chromosome contained seq uences of chromosome 8. Of 40 metaphase cells studied from a mesenteri c IMT in an 8-month-old boy, 12 showed clonal aberrations, characteriz ed as 43,XX,add(1)(p36),add(2)(p24),-6,der(14, 22)(q10;q10),-19. Each of 20 metaphase cells examined from a retroperitoneal IMT in a 14-year -old girl contained complex clonal and nonclonal abberations, characte rized as (q13.1),add(19)(q13.1),+20,-21,-22,+mar1,+1-2mars. The presen ce of clonal chromosomal abberations in all of the three tumors indica tes that the IMT is a neoplastic proliferation.