BACKGROUND: The survival of endometriotic cells in the ectopic site has been 
investigated from the aspect of susceptibility of endometriotic tissues to 
apoptosis. In order to investigate the nature of abnormal survival of 
endometriotic cells in ectopic locations, we compared drug-induced apoptosis in 
endometrial and endometriotic cells.
METHODS: Endometrial stromal cells were obtained from normal endometrium in 11 
patients who underwent hysterectomy for leiomyoma without endometriosis. 
Endometriotic cells were isolated from the chocolate cyst linings of the ovary 
in 13 patients who underwent laparoscopic surgery. Cells were cultured in the 
presence or absence of staurosporine. Apoptotic cell death was evaluated by 
staining nuclei with propidium iodide and phosphatidylserine (a marker of early 
apoptotic events) with Annexin V as well as by DNA fragmentation assay. The 
number of viable cells was estimated by modified MTT 
[3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromide WST-8] assay.
RESULTS: After 3 h of exposure to staurosporine, >50% of the endometrial stromal 
cells became Annexin V positive. In contrast, >30% of the endometriotic cells 
were Annexin V positive. DNA fragmentation was not clearly induced in the 
endometriotic cells. Less than 20% of the endometrial cells survived after 
staurosporine exposure, while >40% of the endometriotic cells survived. Cell 
death induced by staurosporine was partially blocked by incubation with the 
caspase inhibitor, N-benzyoxycarbonyl-Val-Ala-Asp(OMe)fluoromethyl-ketone 
(ZVAD-fmk), suggesting that a caspase cascade may play a role in the cell death 
process.
CONCLUSIONS: Attenuated susceptibility to apoptosis in endometriotic stromal 
cells may be associated with abnormal survival in ectopic sites in an 
environment that is probably unfavourable. These results may be implicated in 
the pathophysiology of endometriosis.