Gene expression profiles of ovarian low-grade serous carcinoma resemble those of fallopian tube epithelium.

Objective: The cell of origin of ovarian low-grade serous carcinoma (LGSC) remains unclarified. Our recent morphologic and immunophenotypic study suggests that most LGSCs may be derived from the fallopian tube. The purpose of the current study was to gain further insight into the origin of LGSC at the molecular level.

Methods: RNA-seq analysis was performed on a total of 31 tissue samples including LGSC (n=6), serous borderline tumors (SBT, n=6), fallopian tube epithelia (FTE, n=5), ovarian surface epithelia (OSE, n=4), and human peritoneal mesothelia (HPM, n=4). HGSC cases (n=6) served as a positive control. Gene expression profiles were compared and analyzed. To validate the findings from the gene expression array study, we selected the highly differentially expressed genes (PAX8, CDH1, FOXA2, and ARX) as well as those corresponding proteins and examined their expression levels in tissue samples of ovarian serous tumors, fallopian tube, ovarian surface epithelia, and peritoneal mesothelia.

Results: Dendrograms revealed that OSE samples clustered with HPM, while ovarian serous tumors, including LGSC, SBT and high-grade serous carcinoma (HGSC), clustered with FTE. Furthermore, LGSC showed a significantly closer relationship with FTE than with OSE and HPM samples. PAX8, CDH1, and FOXA2 were highly and specifically expressed in serous tumors and FTE samples but not in OSE samples. In contrast, ARX was mainly expressed in OSE samples but not in FTE and serous tumors.

Conclusions: The findings of the current study provide further evidence at a molecular level that the fallopian tube is likely the cellular source of LGSC. This finding may enable new prevention strategies, improve early detection, and allow novel therapies to be tested.