**3. Results**

Descriptive data of the study participants and the characteristics of the tumors are presented in Table 1.


**Table 1.** Clinical data of the study participants and tumor characteristics.

cSCC—cutaneous squamous cell carcinoma; AK—actinic keratosis.

The serum levels of TSA and LSA were higher in the cSCC group compared to the controls. In the AK group, only the TSA levels were higher compared to the control group. In addition, there were significant differences between the cSCC and AK groups. The serum levels of ST6GalI and NEU3 were higher in the cSCC group and AK group compared to the controls, the differences were statistically significant only when we compared cSCC patients to the control group. In addition, there were significant differences between the cSCC and AK groups (Table 2, Figure 3).

The rate of synthesis of sialoglycoconjugates and their rate of enzymatic degradation, expressed by the ST6GalI/NEU3 ratio, is 1.64 times lower in the cSCC group compared to the control group (*p* < 0.01) and 1.53 times lower compared to the AK group (*p* < 0.01).

There were statistically significant positive correlations between the serum levels of TSA and LSA and the tumor characteristics (diameter, depth of invasion, and Ki67 index) (Table 3). There were also statistically significant positive correlations between the serum levels of ST6GalI and the tumor characteristics (diameter and Ki67 index) (Table 3).


**Table 2.** The serum levels of TSA, LSA, ST6GalI, and NEU3 in the studied groups expressed as the mean ± standard deviation.

cSCC—cutaneous squamous cell carcinoma; AK—actinic keratosis; TSA—total sialic acid; LSA—lipid-bound sialic acid; ST6GalI—betagalactoside 2,6-sialyltransferase I; NEU3—neuraminidase 3; *p*-significance level, *p* \*—triple comparison of the groups, *p* \*\*—pairwise comparison of the groups.

**Figure 3.** The serum levels of TSA, LSA, ST6GalI, and NEU3 in the studied groups (A = cSCC group, B = AK group, C = control group).



cSCC—cutaneous squamous cell carcinoma; TSA—total sialic acid; LSA—lipid-bound sialic acid; ST6GalI beta-galactoside 2,6-sialyltransferase I; NEU3—neuraminidase 3; Ki67—proliferative index; rho—correlation coefficient; *p*—significance level. \*—statistically significant.
