Abstract
Fibroblasts are a major component of cancer tissue and known to contribute to cancer progression. However, it remains unknown whether they are derived from local fibroblasts or of other origin. This study was designed to identify the contribution of local stromal cells to cancer stroma in human epithelial ovarian cancer. Seventy-six cases of surgically resected primary ovarian carcinoma (48 cases confined to the ovaries and 28 cases with distant metastases) and 17 cases of secondary ovarian tumor (e.g. colon cancer metastasized to the ovary) were enrolled in this study. The tissues were immunostained for forkhead box protein L2 (FOXL2), a transcription factor crucial for ovarian development and function, and markers for cancer-associated fibroblasts (CAFs) and inflammatory cells. Under normal condition, FOXL2 expression was restricted to ovarian stromal cells and some other types of cells in female genital tracts and never found in other sites of the body. FOXL2-positive cells were found in all primary and secondary tumors in the ovary, and were the dominant stromal cells in most cases. In contrast, only a few FOXL2-positive cells were found in peritoneal seeding sites of four serous carcinoma cases, and all the other tumors at extraovarian sites had no FOXL2-positive cells. FOXL2-positive cells in the ovarian lesion variably expressed CAFs markers, such as alpha-smooth muscle actin and fibroblast activating protein, as determined by double immunostaining. Background inflammation, but not histological subtype or origin of the neoplasm seemed to correlate with the proportion of FOXL2-positive cells. These results suggest that ovarian stromal cells are the main source of cancer stroma in the ovary but do not seem to move to distant sites via circulation together with tumor cells. Our results also support the hypothesis that cancer-associated fibroblasts may originate locally, which was previously demonstrated using animal models.
Highlights
Cancer tissue is composed of tumor cells and stromal cells, including fibroblasts, vascular endothelial cells and leukocytes
forkhead box protein L2 (FOXL2)-positive stromal cells are abundant in the stroma of ovarian lesions
We histologically analyzed the presence of local stromal cells in human ovarian cancer tissues by examining the expression of FOXL2, a marker virtually specific to ovarian stromal cells
Summary
Cancer tissue is composed of tumor cells and stromal cells, including fibroblasts, vascular endothelial cells and leukocytes. Little is known about the source of CAFs. Several studies based on human tissue have shown that stromal cells in ovarian cancers have features of steroid hormone-producing cells [4,5,6]. Several studies based on human tissue have shown that stromal cells in ovarian cancers have features of steroid hormone-producing cells [4,5,6] This finding may support the idea that ovarian CAFs are from ovarian stromal cells. Studies based on animal models stress the importance of circulating cells such as bone marrow-derived stromal stem cells as the source of CAFs in various cancers, including ovarian, stomach, breast, and pancreatic cancer [7,8,9,10,11]
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