Leiomyosarcomas are malignant smooth muscle tumors characterized by a spectrum of histopathologic features and clinical behavior. Gene expression profiling of leiomyosarcomas may identify differential gene signatures that may allow for the clinical stratification of the tumors. Typically, surgical specimens from these tumors are large and manifest a variegated macroscopic appearance. Because of their large size at the time of diagnosis, sufficient tissue is available for regional and clonal heterogeneity assessment. However, if the gene expression profiles of samples taken from different locations in the tumors are drastically different, biologic classification on the basis of random sample analysis may not be adequate. Therefore, to assess intertumor and intratumor heterogeneity, the authors performed a gene expression study using leiomyosarcoma specimens from three excised sarcomas from an equal number of different patients. Comparisons between tumor and normal samples from the three patients as well as between carefully mapped peripheral and core specimens from the same tumor (excised from one of the patients), were performed. Analysis of the expression profiles demonstrated minimal intratumor variations compared with intertissue variations, indicating homogeneous tumor specific gene expression profiles. The authors also identified genes that are expressed differentially in tumor and normal tissue. Cancer 2002;94:2069–75. © 2002 American Cancer Society.