['Atypical fibroxanthoma (AFX) and undifferentiated high grade pleomorphic sarcoma (UpS) are histologically very similar, if not identical. However, they differ significantly in clinical outcome.', 'We used comparative genomic hybridization (CGH) to screen 24 AFX and 12 UpS for genomic alterations.', 'DNA copy number changes were observed in 20/24 AFX and in all UpS. The most frequent alterations occurring with comparable frequency in both tumors were deletions on chromosomes 9p and 13q. We also detected statistically significant differences of genetic alterations between the two tumors concerning deletions on 1q, 3p, 5q, 11p, 11q, gains on 7q, 12q and high level gains on 5p and 11q.'] Does cGH analysis show genetic similarities and differences in atypical fibroxanthoma and undifferentiated high grade pleomorphic sarcoma?