EGFL7 expression has been previously analyzed in one study on human ovarian cancer tissue samples derived from 177 patients . In that study immunohistochemical staining for EGFL7 was performed using formalin fixed paraffin-embedded tissue microarrays. 72 of 177 analyzed cases (40.7%) had tumors with serous histology, but information about grading was not specified . High levels of EGFL7 expression were noted in 23 of 72 (31.9%) serous cancers. Survival analysis performed for the entire cohort showed that the epithelial ovarian cancer patients having tumors with high EGFL7 expression had a poorer DFS but similar OS to those with low EGFL7 expression .
Here, we analyzed EGFL7 mRNA transcripts in HGOSC using different methodology, thus, the results of both studies are difficult to compare.
Interestingly, our study supports the suggestion that EGFL7 expression is frequent in epithelial ovarian cancers as we detected EGFL7 mRNA transcripts in 13 of 59 (22.03%) HGOSC cases. Unfortunately, we did not manage to perform quantitative analyses of mRNA in microdissected tissue samples, thus, the impact of intensity of expression of EGFL7 mRNA on OS and PFS was not assessable. However, EGFL7-status of tumor microenvironment (cancer epithelium and adjacent endothelium) had no predictive and prognostic value in analyzed cohort of HGOSC patients.
EGFL7-expression levels were found to correlate with a higher tumor grade in gliomas  and colon cancer , not influencing the prognosis. However, it conferred poorer prognosis and higher metastatic score in hepatocellular carcinoma , but better prognosis and absence of lymph node invasion in human breast cancer . These ambiguous results indicate that EGFL7 expression in human cancer needs to be carefully analyzed as EGFL7 may play a
complex role in cancer biology depending on cancer origin [23–26] and the source of EGFL7 secretion: cancer cells, endothelium or both.
Since it had been proven that EGFL7 is plasma membrane-associated sialidase, which could accumulate in distant tissues from the producing cells , it is impossible to answer if expression of EGFL7 observed in OvCas  comes from activated cancer epithelium or up-regulated endothelial cells in the surrounding stroma. Therefore, we had decided to analyze the impact of EGFL7 on diapedesis using LCM technology, which enables to harvest the epithelial and endothelial cells directly to give histologically enriched cell populations for separate qPCR analyses .
We expected to detect EGFL7 mRNA at least in endothelial cells as these reflect upregulation of EGFL7 gene in activated cancer vessels due to neoangiogenesis and/or inflammatory process. Presence of EGFL7 mRNA transcripts found in microdissected cancer cells indicates the endogenic activation of EGFL7 gene in human HGOSCs. To the best of our knowledge this is the first study documenting activation of EGFL7 in human HGOSC. Interestingly the frequency of epithelial and endothelial activation of EGFL7 was comparable. Further, ICAM-1 was also found to be expressed both on cancer epithelium and endothelium of adjacent stromal vessels thus we decided to assess the correlation between EGFL7 and ICAM-1 matched according the source of origin.
Although it was suggested that EGFL7 negatively regulates the expression of ICAM-1 in endothelial cells  we did not find the difference in the intensity of ICAM-1 expression between endothelium with different EGFL7-status. Similarly lack of difference of ICAM-1 expression was observed for cancer ICAM-1 expressing cells with different Egfl7-statuses.
Our understanding of the role of ICAM-1 in ovarian cancer development remains limited. The elevated expression of ICAM-1 in freshly isolated ovarian cancer cells  suggest that ICAM-1 expression may promote the malignant progression of ovarian cancer. Findings of studies on other malignant tumors suggest that ICAM-1 contributes to carcinogenesis by at least two mechanisms. It mediates the accumulation of inflammatory cells, which facilitates the instability of the tumor environment, triggers tumorigenesis, and maintains the release of trophic factors to enhance cancer cell survival [29, 30]. Second, ICAM-1 partially mediates the invasive and metastatic potential of cancer cells [29–33]. These observations were not confirmed for our cohort of HGOSC patients as we found that cancer-ICAM-1 expression was not correlated with FIGO stage and lacked prognostic significance.
To assess the potential impact of EGFL7 on diapedesis we decided to compare intraepithelial immune infiltrates between tumors having EGFL7 activated in cancer nests and/or adjacent vessels and those without EGFL7 activation.
Presence of EGFL7 mRNA transcripts in epithelium and/or endothelium of tumor microenvironment was associated with a lower influx of adaptive immune effectors (CD4 + and CD8 + lymphocytes) into cancer nests. This provides direct information that in some part, immune escape is achieved by limiting the influx of immune effectors into cancer tissue by activation of EGFL7. The role of epithelial and endothelial EGFL7 should be further evaluated in HGOSCs.
The weakness of the current study is the lack of quantitative assessment of EGFL7, the retrospective design and the small size of cohort involved. Its strength lies of separate analyses of EGFL7 transcripts in epithelium and adjacent endothelium of histologically homogenic group HGOSC tissue samples and consistency of the treatment of patients under uniform standards enabling the assessment of the prognostic significance of all the analyzed biomarkers.
Conclusion: Endogenic EGFL7 activation in cancer cells and its upregulation in endothelium are frequent in HGOSCs and could negatively impact diapedesis. EGFL7 associated down-regulation of ICAM-1 was not observed. Function and predictive value of EGFL7 mRNA transcripts should be evaluated in larger cohorts.