Endometrial stromal sarcoma (ESS) of the uterus is a rare uterine malignancy 
that has not been characterized in detail. To characterize the phenotype of ESS 
of the uterus, we extracted RNA from ESS and the stroma of normal endometrium 
using a tissue microdissection system and compared the expression profiles in 
the two tissues. After suppression subtractive hybridization and differential 
screening, we detected the metastasis-associated lung adenocarcinoma transcript 
1 (MALAT-1) gene as one of the major genes upregulated in ESS, and a full-length 
placental cDNA clone (CS0DI066YJ10) as one of the major genes downregulated. The 
results were confirmed by in situ hybridization in four resected specimens of 
ESS and 36 biopsy specimens of normal endometrial tissue. All ESS (4/4) and all 
cases of endometrial stromal cells in the proliferative phase (13/13) were 
positive for MALAT-1, but samples of normal stroma in the secretory phase and 
menopausal state included some that were negative or weakly positive for MALAT-1 
(5/13 and 3/10, respectively). In contrast, all ESS and 12 of 13 cases of 
stromal cells in the proliferative phase were negative for the full-length 
placental cDNA clone but 10 of 13 cases of endometrial stromal cells in the 
secretory phase were positive for transcripts of the gene (P < 0.05). These 
results indicated that endometrial stromal cells have different phenotypic 
characteristics between proliferative and secretory phases and the tumor cells 
of ESS have the phenotypic character of endometrial stromal cells in the 
proliferative phase.