Spread of endometriosis to pelvic sentinel lymph nodes: gene expression analysis

Endometriotic spread to the lymphatic system has been described, but little is known about the molecular events and changes in gene expression associated with this process. We sought to determine the expression levels of a panel of 28 genes in samples of primary endometriosis lesions (EL), isolated endometriotic-like cells (IELC)-positive pelvic sentinel lymph nodes (PSLN), and IELC-negative PSLN, in order to identify candidate genes that may play a role in this process.

Quantitative real-time PCR and immunohistochemistry (IHC) of primary EL and PSLN samples with and without IELC from patients with ovarian and/or peritoneal endometriosis.

Gene expression was analyzed in EL (n=13), IELC-positive PSLN (PSLN+, n=11), and IELC-negative PSLN (PSLN-, n=8). Gene expression differences between PSLN+ and PSLN- were analyzed and evaluated in relation to their expression levels in EL. Genes expressed at high levels in EL but not in PSLN- and known to be expressed in IELC (such as ESR1, PGR) served as controls and the expected gene dilution effect was clearly observed. Expression of a set of genes (CXCR4, CD68, MKI67, and CD44) was found to be higher in PSLN+ vs. PSLN-, while lowest in EL, indicating upregulation in IELC. In contrast, EPCAM and E-cadherin, which were strongly expressed in EL, were not found to be expressed in PSLN+, and thus likely absent from IELC. IHC confirmed the expression of CXCR4, CD44s, and CD44v6 in IELC, as well as the absence of E-cadherin from IELC.

Our data indicate that spread of endometriosis to PSLN is accompanied by differential expression of several genes, including EPCAM, CDH1 (E-cadherin), CXCR4, and CD44, suggesting an involvement of CD44 splice variants as well as CXCR4 signalling in this process.