Atypical lipomatous tumor with structural rearrangements involving chromosomes 3 and 8.

[well-differentiated liposarcoma]

Atypical lipomatous tumor (ALT ) is an intermediate (locally aggressive ) mesenchymal neoplasm with the potential to dedifferentiate to higher grades over time . It is cytogenetically characterized by the presence of one or more supernumerary ring and giant marker chromosomes . These abnormal chromosomes invariably contain amplified sequences derived from the 12 q 14 -15 region . We describe a unique cytogenetic finding of ALT arising in the right lower back of a 42 -year -old man . Magnetic resonance imaging demonstrated a predominantly fatty mass with irregularly thickened , linear , swirled , and nodular septa . Contrast-enhanced fat-suppressed T 1 -weighted images showed significant enhancement of the non-adipose areas . A sub-extensive resection was performed . Histologically , the tumor consisted predominantly of mature fat cells with atypical stromal cells and multivacuolated lipoblasts . Immunohistochemically , the tumor cells were positive for p 16 (diffuse and strong signal ) and cyclin-dependent kinase-4 (focal and weak signal ) but negative for murine double -minute 2 . Cytogenetic analysis displayed a t (3 ;8 )(q 28 ;q 13 ) translocation as the sole anomaly or concomitant with a few other numerical and structural alterations . There has been no evidence of local recurrence two months after surgery . To the best of our knowledge , this is the first case of ALT with structural aberrations involving chromosomes 3 and 8 , associated with an absence of 12 q rearrangements .