**6.1 Vascular endothelial growth factor, VEGF**

VEGF is a highly specific vascular endothelial cell mitogen and an angiogenic factor associated with platelet-derived growth factor (PDGF) structure. It is also known as vascular permeability factor (VPF), due to its permeabilization of blood vessels [24]. It is a subfamily of growth factors and belongs to a family of plateletderived growth factors of cystine knot growth factor. VEGF is divided into the following groups: VEGF-A, VEGF-B, VEGF-C, VEGF-D, VEGF-E and placental growth factor. VEGF binds to three transmembrane receptors (VEGFR1, VEGFR2 and VEGFR3). This receptor initiates downstream signaling through intracellular tyrosine kinase activity [25]. In fact, VEGF family members are playing an important role in the physiological angiogenesis of adults. Like wound healing, ovulation and pregnancy [26].

Activation of the VEGF/VEGF receptor (VEGFR) axis may trigger multiple signaling networks. Consequently, this may lead to endothelial cell survival, mitosis, migration and differentiation, vascular permeability and mobilization of endothelial progenitor cells (EPCs) from the bone marrow into the peripheral circulation [27]. On ligand binding, VEGFR-2 dimerization results in kinase activation and autophosphorylation of tyrosine residues. Activation of PKC may stimulate the Raf/MEK/ERK pathway, which accelerates the cell proliferation. Ca2+ mobilization and PKC activation are playing the key role in signaling events for VEGF-A-induced vascular permeability through activation of endothelial nitric oxide synthase activity [28].

The sword has double sides. VEGF participates in the pathogenesis of cancer, proliferative retinopathy and rheumatoid arthritis [29]. Its antibodies have shown therapeutic potential to inhibit tumor growth in vivo by inhibiting tumor-induced angiogenesis [30]. VEGF overexpression is associated with a variety of tumor progression and poor prognosis, including colorectal cancer [31], pancreatic cancer [32], gastric cancer [33], breast cancer [34], lung cancer [35], prostate cancer [36] and melanoma [37]. This unique protein aids tumors grow and can be used for cancer treatment if used properly.

EGFR signal transduction pathway can directly participate in tumor pathogenesis and progression [49]. EGFR overexpression plays a major role in carcinogenesis in cancer development [50]. Overexpression of EGFR accounts for 90% in pancreatic cancer cells [51]. Specifically, the aberrant activity of EGFR may impact the

Mutation of EGFR may induce the resistance of tyrosine kinase inhibitors (TKIs) [53]. Notably, in tumor angiogenesis, vascular endothelial growth factor receptor-2 (VEGFR-2) plays a key role, and inhibition of VEGFR-2 signaling pathway has become an attractive cancer treatment method [54]. The binding of VEGF to VEGFR-2 stimulates the signaling pathway (PI3K/Akt, p38MAPK) that mediates several cellular functions. Besides, glycoproteins, EGFR and VEGFR-2 are in close correlation. Inhibition of EGFR can also reduce VEGF expression, while VEGFR-2 targeting can enhance the anticancer activity of EGFR inhibitors. Therefore, the dual inhibition treatment of EGFR and VEGFR-2 has a good effect and represents a promising cancer treatment. Recently, several EGFR/VEGFR-2 dual inhibitors have been discovered, such as vandetanib showing effective inhibitory activity on EGFR

A receptor tyrosine kinase is associated with cell proliferation and survival. Epidermal Growth Factor Receptor, EGFR, is overactive in many epithelial-derived tumors. It has been reported that EGFR is not related to its kinase activity, but rather maintains basal intracellular glucose levels to prevent autophagic death of cells. Despite the presence of chemotherapeutic drugs and tyrosine kinase inhibitors, this function of EGFR allows tumor cells to have higher viability [56]. EGFR inhibitors for cancer therapy are rapidly evolving in the broad context of cancer therapy, and in those patients achieving significant tumor response to EGFR inhib-

itors. Most patients will eventually exhibit disease progression, suggesting

ies by Ko et al. showed that subjects treated by cetuximab, bevacizumab and gemcitabine had 5.41 months in OS and 4.17 months in PFS. Propper et al. in 2014 tested Erlotinib to treat APC, and only achieved 4.0 months of OS and 1.5 months of PFS, **Table 4** [44, 58]. Ko reported the incidence of severe (grades 3–5) toxicity, comparable to the use of gemcitabine as a single agent in this patient population which may reflect a relatively short duration of treatment due to lack of efficacy. Moreover, it is difficult to explain the quality of life analysis based on the number of patients completing the series of questionnaires and the overall time the patients stayed in the study [44]. Propper concluded that there is limited evidence to support the use of predictive biomarkers for patients with pancreatic cancer who could

acquired resistance. This reminds us that increasing our ability to recognize tumors that depend on EGFR signaling growth is critical for the best choice of treating

Unfortunately, two clinical trials showed that the results failed via EGFR. Stud-

KRAS protein plays a key role in human cancer but has not yet succumbed to

There are currently no therapeutic interventions for KRAS. Pharmacological agents that are speculated to inhibit KRAS include farnesyltransferase inhibitors that block the binding of KRAS to the cell membrane. These drugs have failed in clinical studies. Antisense oligonucleotides and engineered microRNAs (miRNAs) have been used as an alternative to targeted mutations in KRAS without disrupting

therapeutic attacks [59]. The search is now focused on targeting alternative pathways that are activated in mtKRAS cells, to circumvent or prevent drug

development and growth of tumor cells [52].

*DOI: http://dx.doi.org/10.5772/intechopen.89976*

*What Are the New Challenges of the Current Cancer Biomarkers?*

and VEGFR-2 [55].

patients [57].

resistance [60].

**135**

benefit from targeted therapies [58].

**6.3 Kirsten rat sarcoma viral oncogene homolog, KRAS**

Early in 1971, Folkman first proposed the idea of angiogenesis. He believed that tumor growth and proliferation are closely related to angiogenesis and could be used as a targeted tumor therapy procedure [38]. Subsequently, countless scientists gathered in the field of VEGF to study the molecular mechanism of VEGF in tumor angiogenesis. They have also used it as a drug target to block the formation of blood vessels, thereby inhibiting tumor growth [39]. Studies have shown that the mechanism of anti-VEGF inhibitors may involve a variety of signaling pathways, such as FGF, D114, PGF/VEGFR1 and VEGF-C/VEGFR2. At least some of these pathways can increase the efficacy of VEGF inhibitors [40]. The anti-tumor drugs were developed with VEGF as the main target area. Like anti-VEGF humanized monoclonal antibody, VEGF-targeted antibody, protein kinase inhibitor and tumor vaccine [41, 42]. However, in the clinical application of anti-antigenic drugs, reliable biomarkers have not been found to screen the target population before patient improvement.

Our data disclosed that there were two studies reporting successful outcomes [14, 19], two studies reported neutral outcomes [21, 22] and four studies reported negative outcomes [43–46]. The results from the above eight trials remain controversial.

Regarding successful outcomes, Raymond et al. found that neuroendocrine tumors may be particularly sensitive to the combined inhibition of VEGFR and PDGFR. As for the neutral outcomes [14], Spano et al. used the gemcitabine + axitinib to treat the APC [21]. However, results differ from the results of Phase III trials in which erlotinib + gemcitabine confers the greatest survival advantage for patients with ECOG status 2 and metastatic disease, it possibly due to the mechanism of action between different EGFR and VEGFR inhibitors. Moreover, Hobday et al. found that the median PFS in the gefitinib trial was only 3.7 months which was even lower than the placebo group in the phase III trial [22].

With respect to the failed outcomes, Kindler et al. found that the effect of axitinib and gemcitabine on APC was limited to improve the survival period in patients with locally APC [43]. In fact, the results may be related to the gene locus of the VEGF receptor 1 tyrosine kinase domain. Furthermore, Ropugier et al. found that PFS was not significantly improved between the treatment arms. It indicates that blocking the VEGF/VEGFR axis does not lead to the survival of a patient with APC [45]. Nooan et al. study shows that pelareorep combination chemotherapy is not a sufficient solution to overcome the severe immunosuppression prevalent in PCA patients [46].

#### **6.2 Epidermal growth factor receptor, EGFR**

EGFR is one of the transmembrane receptors of epidermal growth factor family members of extracellular protein ligands. Its main function is to regulate various cellular functions including proliferation, movement and differentiation. Its mechanism can be described as the binding of the ligand to EGFR leading to dimerization followed by autophosphorylation of EGFR and activation of downstream signaling pathways. Activation of EGFR triggers multiple signal cascades within the cell, ultimately leading to gene transcription and biological responses [47]. Recently, studies have shown that dimerization occurs even in the absence of ligands, particularly when EGFR is overexpressed, possibly limited to a subset of dimers. Moreover, overexpressed EGFR can dimerize and become tyrosine phosphorylated without ligand [48].

gastric cancer [33], breast cancer [34], lung cancer [35], prostate cancer [36] and melanoma [37]. This unique protein aids tumors grow and can be used for cancer

Early in 1971, Folkman first proposed the idea of angiogenesis. He believed that tumor growth and proliferation are closely related to angiogenesis and could be used as a targeted tumor therapy procedure [38]. Subsequently, countless scientists gathered in the field of VEGF to study the molecular mechanism of VEGF in tumor angiogenesis. They have also used it as a drug target to block the formation of blood vessels, thereby inhibiting tumor growth [39]. Studies have shown that the mechanism of anti-VEGF inhibitors may involve a variety of signaling pathways, such as FGF, D114, PGF/VEGFR1 and VEGF-C/VEGFR2. At least some of these pathways can increase the efficacy of VEGF inhibitors [40]. The anti-tumor drugs were developed with VEGF as the main target area. Like anti-VEGF humanized monoclonal antibody, VEGF-targeted antibody, protein kinase inhibitor and tumor vaccine [41, 42]. However, in the clinical application of anti-antigenic drugs, reliable biomarkers have not been found to screen the target population before patient

Our data disclosed that there were two studies reporting successful outcomes [14, 19], two studies reported neutral outcomes [21, 22] and four studies reported negative outcomes [43–46]. The results from the above eight trials remain contro-

Regarding successful outcomes, Raymond et al. found that neuroendocrine tumors may be particularly sensitive to the combined inhibition of VEGFR and PDGFR. As for the neutral outcomes [14], Spano et al. used the gemcitabine + axitinib to treat the APC [21]. However, results differ from the results of Phase III trials in which erlotinib + gemcitabine confers the greatest survival advantage for patients with ECOG status 2 and metastatic disease, it possibly due to the mechanism of action between different EGFR and VEGFR inhibitors. Moreover, Hobday et al. found that the median PFS in the gefitinib trial was only 3.7 months which was

With respect to the failed outcomes, Kindler et al. found that the effect of axitinib and gemcitabine on APC was limited to improve the survival period in patients with locally APC [43]. In fact, the results may be related to the gene locus of the VEGF receptor 1 tyrosine kinase domain. Furthermore, Ropugier et al. found that PFS was not significantly improved between the treatment arms. It indicates that blocking the VEGF/VEGFR axis does not lead to the survival of a patient with APC [45]. Nooan et al. study shows that pelareorep combination chemotherapy is not a sufficient solution to overcome the severe immunosuppression prevalent in

EGFR is one of the transmembrane receptors of epidermal growth factor family members of extracellular protein ligands. Its main function is to regulate various cellular functions including proliferation, movement and differentiation. Its mechanism can be described as the binding of the ligand to EGFR leading to dimerization followed by autophosphorylation of EGFR and activation of downstream signaling pathways. Activation of EGFR triggers multiple signal cascades within the cell, ultimately leading to gene transcription and biological responses [47]. Recently, studies have shown that dimerization occurs even in the absence of ligands, particularly when EGFR is overexpressed, possibly limited to a subset of dimers. Moreover, overexpressed EGFR can dimerize and become tyrosine phosphorylated

even lower than the placebo group in the phase III trial [22].

**6.2 Epidermal growth factor receptor, EGFR**

treatment if used properly.

*Current Cancer Treatment*

improvement.

PCA patients [46].

without ligand [48].

**134**

versial.

EGFR signal transduction pathway can directly participate in tumor pathogenesis and progression [49]. EGFR overexpression plays a major role in carcinogenesis in cancer development [50]. Overexpression of EGFR accounts for 90% in pancreatic cancer cells [51]. Specifically, the aberrant activity of EGFR may impact the development and growth of tumor cells [52].

Mutation of EGFR may induce the resistance of tyrosine kinase inhibitors (TKIs) [53]. Notably, in tumor angiogenesis, vascular endothelial growth factor receptor-2 (VEGFR-2) plays a key role, and inhibition of VEGFR-2 signaling pathway has become an attractive cancer treatment method [54]. The binding of VEGF to VEGFR-2 stimulates the signaling pathway (PI3K/Akt, p38MAPK) that mediates several cellular functions. Besides, glycoproteins, EGFR and VEGFR-2 are in close correlation. Inhibition of EGFR can also reduce VEGF expression, while VEGFR-2 targeting can enhance the anticancer activity of EGFR inhibitors. Therefore, the dual inhibition treatment of EGFR and VEGFR-2 has a good effect and represents a promising cancer treatment. Recently, several EGFR/VEGFR-2 dual inhibitors have been discovered, such as vandetanib showing effective inhibitory activity on EGFR and VEGFR-2 [55].

A receptor tyrosine kinase is associated with cell proliferation and survival. Epidermal Growth Factor Receptor, EGFR, is overactive in many epithelial-derived tumors. It has been reported that EGFR is not related to its kinase activity, but rather maintains basal intracellular glucose levels to prevent autophagic death of cells. Despite the presence of chemotherapeutic drugs and tyrosine kinase inhibitors, this function of EGFR allows tumor cells to have higher viability [56]. EGFR inhibitors for cancer therapy are rapidly evolving in the broad context of cancer therapy, and in those patients achieving significant tumor response to EGFR inhibitors. Most patients will eventually exhibit disease progression, suggesting acquired resistance. This reminds us that increasing our ability to recognize tumors that depend on EGFR signaling growth is critical for the best choice of treating patients [57].

Unfortunately, two clinical trials showed that the results failed via EGFR. Studies by Ko et al. showed that subjects treated by cetuximab, bevacizumab and gemcitabine had 5.41 months in OS and 4.17 months in PFS. Propper et al. in 2014 tested Erlotinib to treat APC, and only achieved 4.0 months of OS and 1.5 months of PFS, **Table 4** [44, 58]. Ko reported the incidence of severe (grades 3–5) toxicity, comparable to the use of gemcitabine as a single agent in this patient population which may reflect a relatively short duration of treatment due to lack of efficacy. Moreover, it is difficult to explain the quality of life analysis based on the number of patients completing the series of questionnaires and the overall time the patients stayed in the study [44]. Propper concluded that there is limited evidence to support the use of predictive biomarkers for patients with pancreatic cancer who could benefit from targeted therapies [58].

#### **6.3 Kirsten rat sarcoma viral oncogene homolog, KRAS**

KRAS protein plays a key role in human cancer but has not yet succumbed to therapeutic attacks [59]. The search is now focused on targeting alternative pathways that are activated in mtKRAS cells, to circumvent or prevent drug resistance [60].

There are currently no therapeutic interventions for KRAS. Pharmacological agents that are speculated to inhibit KRAS include farnesyltransferase inhibitors that block the binding of KRAS to the cell membrane. These drugs have failed in clinical studies. Antisense oligonucleotides and engineered microRNAs (miRNAs) have been used as an alternative to targeted mutations in KRAS without disrupting


Unfortunately, Chung et al. tested pharmaceutical target via KRAS protein, whereas the result was unsuccessful. The results showed that the OS and PFS of patients treated by Akt Inhibitor MK2206 and selumetinib were 3.9 and 1.9 months, respectively, see **Table 4** [65]. The results indicated that the strategy of utilizing two or more kinase inhibitors is subject to the challenge of toxicity overlap. These toxicities will significantly block the delivery of effective inhibitory amounts of both drugs in vivo. However, a major disadvantage factor is the delay in toxicityrelated treatment and the frequency of dose reduction in the experimental group

APC reserves unpredictable mechanisms to maintain a highly resistant phenotype. The genetic and epigenetic alterations of the APC lead to the resistance of the

Nowadays, many biomarkers have been on board to improve the clinical treat-

We can assume that with the development of truly effective treatments and clinically useful markers for early detection of the disease, better combination of markers to advanced pancreatic cancer. In the meanwhile, researchers are trying to detect magnificently predictive biomarkers to decide the treatment strategy and permit practitioners to adequately evaluate and propose individualized treatment

Clearly, there is a need to better understand the underlying signaling networks that drive pancreatic cancer progression and potential escape mechanisms. In addition, it is necessary to improve the role of preclinical models of pancreatic cancer

ment outcome of advanced pancreatic cancer. Although these successful biomarkers have provided notable therapeutic effects on advanced pancreatic cancer, the outcomes remain unsatisfactory to the patients and health providers. With the development of the biology of advanced pancreatic cancer, we now expect better biomarkers and conduct therapy by unveiling the tumor microenvironment and the

through damaging sustained signal suppression [65].

*What Are the New Challenges of the Current Cancer Biomarkers?*

*DOI: http://dx.doi.org/10.5772/intechopen.89976*

mechanism of the mutations (**Figure 1**).

protocols which would give a greater survival rate.

*Difficulties in decision making both for R&D and doctors.*

**7. Conclusion**

chemotherapy.

**Figure 1.**

**137**

#### **Table 4.**

*Clinical trial failed outcome on pancreatic cancer.*

the expression of non-mutant KRAS and have achieved some success in preclinical trials [70].

In recent years, many studies have suggested that the oncogene KRAS plays a major role in controlling cancer metabolism by coordinating multiple metabolic changes [71]. Furthermore, combined inhibition of therapeutic effects and feedback pathways is promising in KRAS mutant cancers. Moreover, it is unclear what specific pathways should be used to optimize treatment response [72].

*What Are the New Challenges of the Current Cancer Biomarkers? DOI: http://dx.doi.org/10.5772/intechopen.89976*

Unfortunately, Chung et al. tested pharmaceutical target via KRAS protein, whereas the result was unsuccessful. The results showed that the OS and PFS of patients treated by Akt Inhibitor MK2206 and selumetinib were 3.9 and 1.9 months, respectively, see **Table 4** [65]. The results indicated that the strategy of utilizing two or more kinase inhibitors is subject to the challenge of toxicity overlap. These toxicities will significantly block the delivery of effective inhibitory amounts of both drugs in vivo. However, a major disadvantage factor is the delay in toxicityrelated treatment and the frequency of dose reduction in the experimental group through damaging sustained signal suppression [65].
