COMBINED MORPHOLOGIC AND KARYOTYPIC STUDY OF 59 ATYPICAL LIPOMATOUS TUMORS - EVALUATION OF THEIR RELATIONSHIP AND DIFFERENTIAL-DIAGNOSIS WITH OTHER ADIPOSE-TISSUE TUMORS

Fifty-nine cases of atypical lipomatous tumors (ALT) of soft tissue (a typical lipomas, well-differentiated liposarcomas) were studied morpho logically and cytogenetically as part of an international collaborativ e study. Forty-nine cases were deeply seated (including retroperitoneu m), and 10 were superficial. Clonal chromosomal abnormalities were fou nd in 55 cases (93%). Supernumerary ring or giant marker chromosomes ( RGCs), the sole consistent alteration, were found in 37 ALTs (63%). Th ey were more common in tumors that were large (p < 0.001), deeply seat ed (p < 0.005), that contained lipoblasts (p < 0.05), and that had mar ked cytologic atypia (p < .05). In a relatively short follow-up period (average, 3 years), only three of 59 cases recurred, one resulting in the patient's death. All three cases had RGCs. Also, five of the six cases that underwent dedifferentiation had RGCs, indicating that RGCs are associated not only with low-grade malignant behavior (in the form of local recurrence) but also with the potential for tumor progressio n. When the karyotypic profile of ALT was compared with that of 233 ot her types of adipose tissue tumors similarly analyzed by the authors, a statistically highly significant correlation (p < 0.0001) was found between ALT and RGCs. These results support the existence of ALT as a distinct tumor subtype that is different from ordinary lipoma and from spindle or pleomorphic lipoma, albeit histogenetically closely relate d to them. It also supports the proposed pathogenetic link between ALT and dedifferentiated liposarcoma. The association between chromosomal and morphologic findings indicates the potential role of karyotypic a nalysis in the differential diagnosis of ALT with ordinary lipoma, spi ndle or pleomorphic lipoma: hibernoma, and myxoid liposarcoma.