OPG, OPN, EGF and VEGF Levels at Individual Breslow Score Stages in Malignant Melanoma

Discussion

Cutaneous melanoma is a highly malignant tumour. Treatment of early stage melanoma has the potential to be more successful than the treatment of melanoma at advanced stages. The Breslow thickness of the tumour (Breslow score) and the status of the sentinel lymph node are still the most important prognostic factors for disease free interval (DFI) and overall survival (OS). As primary tumour thickness increases, there is a significant decrease in survival (7). Patients with thin melanoma and negative sentinel lymph node can be assured that their risk of recurrence is extremely low (8). For early detection ability this study focused on the group with a Breslow score of less than 1 mm (Table III).

Afterwards the study was focused on biomarkers as prognostic factors. Current prognostic factors do not give us accurate information to predict melanoma behavior in individual patients, the aggressiveness of the disease, or the way a tumour might disseminate. The levels of four biomarkers were correlated with the sentinel lymph node status. The Breslow score was used as a control parameter of these correlations (Table IV). As a result, the median Breslow score in the metastatic group was statistically significantly higher than in the group without metastases.

OPG is a potent pro-angiogenic factor, it regulates bone turnover and has additional roles in the immune and vascular systems (9). OPG plays an important role in tumor angiogenesis. Production of OPG is thought to be part of tumor cell survival strategy. A number of studies have been performed assessing the role of OPG in tumorigenesis (10). Lau with collaborators proved the messenger RNA (mRNA) expression of OPG by primary melanoma cells and also by metastatic melanoma cells (11). This study explains our finding of elevated OPG plasma levels in the melanoma group compared to healthy controls (Table II). If we focus on the first Breslow score stage we can see that the use of OPG for early diagnostics of melanoma will be limited. Statistically significant increase of OPG levels was observed starting from the second Breslow score stage (Table III). OPG plasma levels were increased with statistical significance in patients with sentinel lymph node metastases positivity (Table IV), which is a promissing outcome with regards to the potential prognostic value of OPG.

OPN is an important factor in bone remodeling (12). OPN has been also described in the context of diverse physiological roles such as chemotaxis, cell migration, cell adhesion, angiogenesis, apoptosis, cell-extracellular matrix interactions and tumour metastasis. OPN actively promotes the tumourigenic phenotype and contributes to metastasis (13).

High levels of OPN are associated with poor prognosis in a variety of cancers while overall and disease-free interval are inversely related to osteopontin levels (14, 15). Kadkol et al. and Barak et al. performed a study concerning metastatic uveal melanoma where plasma levels of OPN were significantly higher in patients with metastatic melanoma compared to patients with DFI for 10 years and levels of metastatic patients were also significantly higher than those without metastases (16, 17). Barak et al. also proved that OPN plasma levels increase during metastases formation and can be detected as early as 12-18 months prior to CT scans (18). Rangel et al. proved an association between high OPN expression and increased tumour thickness. OPN expression was also an independent significant predictor of sentinel lymph node metastases (19). Our results correlate with all the above mentioned findings. We found elevated OPN plasma levels in the melanoma group compared to healthy controls (Table II). The elevation of OPN was even observed at all individual Breslow score stages (Table III). OPN was also statistically significantly increased in patients with sentinel lymph node metastases positivity (Table IV). OPN levels positively correlated with the increasing tumour thickness. All these facts are promissing for OPN as a marker of early stages and also as a prognostic biomarker.

EGF stimulates growth, proliferation, and differentiation of the cells. According to several studies, EGF has been implicated as a factor indicating tumour progression in certain types of cancers (20). In the study conducted by Bracher et al., EGF was identified as an important factor in the mediation of melanoma lymph node metastases (21). Dadras, in their own study empphasized the crucial role of EGF in the generation of lymphatic vessels. Lymph node metastases are associated with these lymphatic vessels in human melanoma. Lymph node metastases are associated with poor prognosis among patients with melanoma (22). Our findings are in concordance with the findings in the above mentioned studies. EGF levels were found to be statistically significantly higher in the group of melanoma patients compared to the control group but mainly EGF levels were significantly higher statistically in the group of patients with sentinel lymph node metastases compared to the group without metastases (Table IV). This finding supports the ability of EGF to be a prognostic marker.

VEGF naturally occurs as a glycoprotein and is an important factor of vasculogenesis and angiogenesis. VEGF is overexpressed in almost all types of solid cancers (23). Boon et al. found no correlation between VEGF plasma levels and the Breslow score but there was a positive correlation with the sentinel lymph node metastases (24). These results were confirmed by Vihinen et al. or Lugowska et al. (25, 26). Tas et al. observed that circulating levels of VEGF were significantly elevated in patients with melanoma compared to healthy controls but didn't correlate with the Breslow score (27). Similar results were observed in a broad multimarker study from Yurkovetsky et al. (28). Ugurel et al. found that elevated plasma levels of VEGF strongly correlated with poor overall survival and disease-free interval (29). Pelletier et al. measured VEGF during follow-up and onbserved earlier relapse in the patients with the elevated levels of VEGF (30). Our results support the prognostic value of plasma VEGF levels due to statistically significant elevated levels in patients with sentinel lymph node metastases positivity compared to the patients with negative lymph node status (Table IV).

In conclusion, if we focus on the first Breslow score stage of melanoma we can conclude that plasma levels of OPG and OPN are promising biomarkers for use at early stages of melanoma. Besides, OPN can also be used as a prognostic marker. EGF and VEGF appear to be prognostic biomarkers in cases of cutaneous melanoma.