## 3 Results and Discussions
In many tumours, Dkk-1 clearly acts only as an oncogene, but in others, it is found to have an anti-oncogenic role, depending on the setting complexity and/or the given tumour type. It was reported that serum Dkk-1 in patients with osteonecrosis of the femoral head could be correlated with the severity of this pathology. Moreover, increased Dkk-1 expression was associated with bone cell apoptosis in patients with corticosteroid and alcohol intake and progression of osteonecrosis of the femoral head [46]. Researchers stated that the Dkk-1 expression level at clinical stage I in endometrial carcinoma was significantly greater than at other stages [47]. [PERSON] et al. [48] also observed that Dkk-1 levels appeared faster in an early diagnosis of prostate cancer compared to the late stages with bone metastases,suggesting that Dkk-1 expression increases in early-stage cancer and is a necessary early event to support osteolysis. As we well know, Dkk-1 has been associated with multiple myeloma and various types of cancers, including head and neck, lung, breast, liver and bone cancers [3; 6]. [PERSON] et al. discovered that patients with acute infections showed dramatically high levels of Dkk-1 (6072 \(\pm\) 518 pg/mL) in their blood compared to healthy blood donors (1726 \(\pm\) 95 pg/mL) [4; 49]. On the other hand, other researchers found higher Dkk-1 protein levels in myeloma cells from patients with bone lesions when compared to plasma cells from non-myeloma subjects or in plasma cells from patients who had myeloma without bone lesions [50]. A recent study observed that increased levels of serum Dkk-1 were noted in subjects with oesophageal adenocarcinoma, implying that this molecule has a crucial role in inflammation. Additionally, increased Dkk-1 values were associated with unfavourable five-year survival rates and the presence of circulating tumour cells [51]. The same authors noted that significantly lower levels were observed in subjects after neoadjuvant treatment, implying that Dkk-1 may act as a biomarker for treatment monitoring [51]. However, it is not always clear, since a plethora of examples for both sides may be found. Coming back to the obtained results, a question is raised: could the decreased levels of Dkk-1 be bone-loss-protective when observed in low levels in the serum of cancer patients? The obtained low levels could be the effect of the cancer treatment and/or other chronic events in association with periodontal variables. Periodontal disease induces a number of oral environment modifications, and one must not minimize the role of the oral microbiome in the overall systemic ecological balance [52; 53]. More studies are needed in order to suggest an association between bone markers such as the Dkk-1 and progression of radiological damage in ENT cancer subjects. The limitations of our study consist of a small number of analyzed subjects, and a slight imbalance in the females-to-males ratio, which could affect the results. However, this  
Figure 4: Dkk-1: comparative descriptive statistics in the control/test group. is explained by the reduced compliance and willingness of cancer patients to participate in research due to the altered quality of life. Another limitation is the fact that we do not have the follow-up values that would show the variation in time of bone loss and Dkk-1 values according to treatment.