Leiomyosarcomas and benign smooth muscle tumors of the stomach: nuclear DNA patterns studied by flow cytometry.

Paraffin-embedded archival tissue samples were used for determination of DNA ploidy by flow cytometry on 117 surgically resected gastric smooth muscle tumors (44 leiomyosarcomas, 53 leiomyomas, and 20 benign leiomyoblastomas). The technique of Hedley was used for preparation of paraffin-embedded tissue into single dissociated nuclei, and the method of Vindeløv was used for staining with propidium iodide. Among the 53 leiomyomas, the DNA ploidy pattern was diploid in most tumors (87%), except for 2 DNA tetraploid/polyploid and 5 DNA aneuploid samples. In comparison, the 20 benign leiomyoblastomas had more frequent abnormal DNA histograms: DNA tetraploidy/polyploidy in 5 (25%) and DNA aneuploidy in 2 (10%). The DNA histograms of the 44 leiomyosarcomas (including 4 epithelioid leiomyosarcomas) were classified as follows: 20 cases (45%) exhibited a DNA diploid pattern, 14 cases (32%) had a DNA tetraploid/polyploid pattern, and 10 cases (23%) had DNA aneuploid peaks. For the patients with leiomyosarcomas, the DNA ploidy pattern was significantly correlated with survival (P less than 0.001), as were tumor grade (P less than 0.001) and tumor size (P less than 0.05). Furthermore, both benign and malignant gastric smooth muscle tumors with DNA tetraploid/polyploid patterns were significantly larger than those with a DNA diploid histogram (P less than 0.05). DNA ploidy pattern cannot be used for diagnosis--that is, to distinguish malignant from benign gastric smooth muscle tumors. For gastric leiomyosarcomas, however, nuclear DNA ploidy pattern is an easily measured objective determination with important prognostic significance.