# Status Quo of Glycoslation in Cancer: What Is, What Is Not and What Is to Be
## 2 Milestones of Glycoslation in Cancer
### Glycosylation for Cancer Biomarkers  
Cellular glycosylation is coordinated by glycosyltransferases and glycosidases to bring about addition/modification of glycans on proteins and lipids [65]. Glycomics unravels the impact of glycosylation in cancer [66; 67; 68]. Enzymes may be altered because of cancer and can be linked to tumor development. 1-6-N-acetyl-glucosamine/transferase (GnT-V) is overexpressed in various cancers and is interconnected with higher invasive potential [69], metastasis [70], vascular remodeling [71] and tumor growth [72]. Biomarkers that can result in early diagnosis and can be used to design new therapeutic strategies are now needed. This has been accomplished by targeting cancer-associated glycans. [PERSON] et al., in their exhaustive and excellent review have elaborately discussed how aberrant glycosylation is closely interrelated with protein glycoforms which can be used as cancer biomarkers [73]. Aberrant glycosylation is reported to play a key role in cancer progression according to [PERSON] and [PERSON], 2016. The same group has also documented the initiation and progression of cancer bringing about fundamental changes in the glycome [74]. [PERSON] et al. 2016 have reported aberrant glycosylation and have established the link between aberrant glycan composition of prostate cancer cells and disease progression [74]. Glycosylation is reported as the global target for androgen control in the case of patients suffering from prostate cancer. Aberrant CD43 has been established as a cancer biomarker. UN1 monoclonal antibodies (UN1 mAb) have been reported to be able to identify aberrant CD43 glycoforms [75]. Serological assays in clinical practices detect and quantify glycans in cancer patient's serum. Circulating glycoconjugates are used for diagnosis, therapy monitoring, detecting disease recurrence and prognosis. Glycoconjugates, such as sially-Lewis A (Slea) (CA19-9), STn (silyl Tn) (CA72-4) and mucin glycoproteins MUC1 (CA15-3) and MUC16 (CA125) [76; 77; 78; 79], are crucial serum cancer markers. CA125, a transmembrane mucin, is currently the best biomarker for ovarian cancer. Elevated levels of CA125 have been reported in the serum of stage I ovarian cancer patients, 60 months prior to actual diagnosis [80]. High CA125 serum levels have been reported in about 80% of epithelial ovarian cancer patients [78; 81]. CA125 preoperative levels help in the prognosis of ovarian cancer patients, relating to the progression or regression of cancer in the system. CA125 is also ideal for monitoring chemotherapy responses, detecting recurrence and for prognosis [82; 83; 84]. MUC1 is also a transmembrane mucin overexpressed in 90% of breast cancers, and it is evaluated using the CA15-3 assay. CA15-3 is useful in understanding response to anticancer therapy, and prognosis for breast cancer [85; 86; 87; 88]. Increase in CA15-3 prior to treatment can be correlated with inadequate prognosis,  
Figure 1: Mass spectrometry and its variants that have been reported to be used to analyze glycan-based cancer biomarkers. pointing out a failure in treatment [85; 89]. The CA19-9 assay detects sLeA in colorectal, gastric, pancreatic or biliary cancer patients, and it is most sensitive and specific with respect to pancreatic cancer [90; 91]. In the case of colon cancer, patients with high CA19-9 are reported to have a four times greater mortality rate than those with lower. In gastric cancer, prior to surgery CA 19-9 behaves as a prognostic marker and for risk factor assessment for the relapse of gastric carcinoma [92; 93; 94; 95]. The CA72-4 assay detects aberrant sialyl-Tn (STn) in the serum of patients with gastric, colorectal, pancreatic, lung and breast carcinomas [92; 96; 97; 98; 99; 100; 101]. CA72-4, is reported for its role as an independent prognostic factor in gastric carcinoma and in pancreatic cancer [102; 103]. Carcinoembryonic antigen (CEA), is a member of a family of N-glycoprotein, its serum levels act as a marker for a wide range of human carcinomas [104; 105; 106; 107; 108]. [PERSON] et al.