br expression negative absent or weak
expression (negative = absent or weak, and positive = moderate or well characterized. The current study demonstrates that multiple MES
strong) to minimize the risk of over-interpretation of minor changes subtype gene signatures are primarily expressed in stroma rather than
in protein expression across specimens. Two collagen proteins demon- cancer 178603-78-6 (Fig. 1). In addition, several proteins appear differentially
strated different expression levels between the primary and metastatic expressed between primary and metastatic sites including COL5A1,
reduced in 40% (6/15) of cases in the metastatic vs. primary tumor esis that stroma significantly contributes to what is currently considered
Gene selected in this study.
Gene symbol Full name Information References
ACTA2 Alpha-smooth muscle Overexpressed in C1 subtype of OC 
Overexpressed in MES subtype of OC  COL5A1 Collagen type V, alpha 1 Overexpressed in MES subtype of OC [4,5]
Associated with poor OS in HGSOC  COL11A1 Collage type XI, alpha 1 Overexpressed in MES subtype of OC [4,5]
Associated with poor OS in HGSOC  FAP Fibroblast activation protein Overexpressed in C1 subtype of OC 
Overexpressed in MES subtype of OC [3–5] POSTN Periostin Overexpressed in MES subtype of OC [4–6]
Associated with poor OS in HGSOC  p-SMAD2 Phosphorylated SMAD2 TGF-β signaling significantly activated in MES subtype of OC 
TGF-β signaling related to poor OS in HGSOC  VCAN Versican Overexpressed in MES subtype of OC [5,6]
Associated with poor OS in HGSOC 
Upregulated in cancer-associated fibroblasts  ZEB1 Zinc finger E-box binding homeobox 1 Overexpressed in MES subtype of OC [5,6,10]
Fig. 1. Protein expression in MES subtype of HGSOC.
the MES subtype of HGSOC. Stromal activation may play a role in the be-haviors of these aggressive cancers.
It is acknowledged that cancer-associated stroma not only serves as a scaffold for tissue organization and integrity but also affects tumor mi-croenvironment to promote cancer initiation, angiogenesis, invasion, and metastasis [14,15]. The stimulatory contribution of stroma in tumor progression, coupled with the fact that stroma is more geneti-cally stable compared with cancer cells, has led to stroma increasingly being recognized as a therapeutic target [16,17]. In support of this, we recently published that inhibition of TGF-β signaling, which suppresses the cancer-stroma interplay, can delay tumor growth and ascites development in MES subtype HGSOC patient-derived xenografts . In comparison with the advances in our understanding of cancer cell biology, our knowledge of the nature and roles of stromal contribution has lagged. Our findings suggest that molecular classifications are at least partially comprised of stroma signatures: whether this represents signal or response to tumor cells will need to be determined. Improved
understanding of the complicated stromal biology will accelerate the development of effective therapeutic strategies for HGSOC, especially for MES HGSOC. Stroma contains both a cellular component (e.g., fibroblasts, immune cells) and a non-cellular component (e.g., extracellular matrix) [17,19]. How each constituent affects cancer progression is still largely unknown.
Metastasis occurs in the vast majority of high-grade epithelial ovar-ian cancer, making presentation at advanced stage common . After initial surgery, most patients will be left with relatively large volume of microscopic cancer cells, even after complete gross resection. This so-called ‘minimal residual’ model of widespread intraperitoneal disease after initial surgery influences recurrence patterns as these sites often harbor dormant cells. Inhibiting metastatic potential or halting the growth and invasiveness of established metastasis should improve progression free survival. Cancer-associated stroma has been shown to promote tumor progression [16,21]. Our preliminary results demonstrate the collagen proteins (COL5A1 and COL11A1) and TGF-β
Fig. 2. COL5A1 and COL11A1 protein expression in primary vs. metastatic MES subtype of HGSOC.
signaling protein (p-SMAD2) may be differentially expressed in primary vs. metastatic sites.
Collagen is the most abundant constituent of extracellular matrix (ECM). Collagens degrading, re-depositing, cross-linking and stiffening are the characteristics of stroma activation to promote cancer metasta-sis [19,22]. Increases and decreases of collagen are coordinated recipro-cally to promote tumor metastasis and invasion . Microarray data analysis from whole tumors demonstrates that both COL11A1 and COL5A1 are enriched in metastatic vs. primary tumors in OC . Though limited in sample size, we confirm these observations showing that COL11A1 is increased in metastatic vs. primary tumors (Fig. 2D–F). Contrary to the increase of COL11A1 in stroma, COL5A1 appears reduced in stroma associated with metastases (Fig. 2A–C). Until now only a few studies have been published on COL5A1. Previous research suggested that high expression of COL5A1 mRNA from whole tumors was associ-ated with metastasis and/or poor survival and that COL5A1 knockdown in vitro in cancer cell lines inhibited cell migration and invasion in lung adenocarcinoma, gastric cancer and OC [23–25]. Our results are based on small numbers and differences in techniques, primary cancers vs. cell lines, and the focus on cancer cells vs. stroma likely play a role in explaining these differences.