Primary aim of the present study was to evaluate the serum leptin concentration in advanced gastrointestinal cancer patients. We have found a significant decrease in serum leptin concentrations of cancer group compared to controls. Although it is still controversial, serum leptin concentration has been reported to be lower than controls, especially in the lung and colorectal cancer, in the literature. It has been suggested that low serum leptin concentration may be related to decreased body fat mass in this subjects [13
]. Tessitore et al [12
] reported that patients with breast cancer had higher serum leptin concentration than controls. However, they did not observed any increase in serum leptin concentration in patients with colorectal cancer compared to controls. No mechanism related to these results has been suggested by this author [12
]. Median weight loss has reached up to 8% in our cancer patients. Therefore decrease in leptin concentration may be related to decreased body fat mass which was developed secondary to weight loss in our patients.
It has been reported that healthy women have more adipose tissue and consequently have higher leptin concentrations than men with equivalent BMI [14
]. Similarly, in the present study, serum leptin concentrations were higher in women than in men in controls, while not in cancer group. Linear regression analysis has shown that serum leptin concentration was only related with gender in controls, however, there was no relationship between gender and serum leptin concentration in cancer group. This observation may indicate that gender factor is not a determinant for serum leptin level in patients with advanced gastrointestinal cancer. As reported previously [14
], other parameters such as BMI and age were not related with serum leptin concentration neither in controls nor in cancer patients. Inflammatory cytokines have been suggested to influence serum leptin concentrations [17
], whereas conflicting results have been reported in the literature [18
]. The influence of these cytokines on serum leptin concentrations couldn't be investigated in the present study.
In our study, body weight loss percentage was not related with leptin concentration in cancer group in linear regression analysis. This finding was consistent with the literature [13
]. In the healthy subjects a decrease in serum leptin concentration appears to stimulate an increase in neuropeptide Y from the hypothalamus and this, in turn, results in increased appetite and decreased energy utilization [5
]. Although decrease in serum leptin concentration in cancer patients has been reported in previous studies, no increase in appetite and decrease in energy expenditure have been observed in these subjects. This finding has been suggested to be due to a block in the hypothalamic response to low circulating leptin concentrations in such cancer patients [13
]. In the present study, the lack of relationship between serum leptin concentration and body weight loss percentage, and decrease in serum leptin concentration suggested that leptin level is not a causative factor in weight loss in patients with gastrointestinal cancer.
In addition to findings mentioned above, we have also found no difference between patients with advanced gastric and colorectal cancer in regarding to serum leptin concentrations. This finding has not been reported in previous studies. This suggested that serum leptin concentration is not affected from the site of advanced stage cancer of gastrointestinal tract and it is constantly low in these subjects.