THE CHANGE OF BLOOD INSULIN LEVEL IN PATIENTS WITH BRAIN GLIOBLASTOMA DURING ADJUVANT RADIATION THERAPY

Aim: To analyse the level of insulin oversecretion in patients with glioblastoma, which during adjuvant radiation therapy (aLT) received dexamethasone at daily doses of 4 or 8 mg.
Materials and methods: The study included 81 patients with brain glioblastoma. Dexamethasone 4 mg was administered intramuscularly for 6–7 weeks (duration of aLT) to 66 patients who had not been previously treated with dexamethasone (group 1). In group 2, 15 patients received dexamethasone at daily dose of 8 mg i.m. for 6 to 7 weeks before aLT, whereas during aLT, their daily dose of dexamethasone was reduced to 4 mg. Levels of C-peptide, insulin and cortisol were studied at one day before and one day after completion of adjuvant radiation therapy.
Results: Patients from group 1 showed a significant increase of blood insulin (from 64.2 ± 40.9 to 105.2 ± 124.9 pmol/l, р < 0.05) and C-peptide (from 2.3 ± 1.0 to 3.2 ± 1.3 ng/ml, р < 0.05) within their reference ranges, as well as a significant decrease in blood cortisol (from 513.1 ± 163.6 to 82.7 ± 114.7 nmol/l, р < 0.001) at 6 to 7 weeks after dexamethasone administration at daily dose of 4 mg. Increase of daily dexamethasone dose from 4 to 8 mg did not lead to a substantial increase in blood insulin and C-peptide levels, but the level of C-peptide in group 2 exceeded its upper normal limit (3.8 ± 1.2 ng/ml). After reduction of dexamethasone dose in group 2 from 8 to 4 mg, there were no major changes in insulin and C-peptide levels, whereas the level of blood cortisol in these patients continued to decline (to 33.7 ± 13.4 nmol/l, р < 0.05).
Conclusion: The use of dexamethasone at a daily dose of 4 to 8 mg in glioblastoma patients during adjuvant radiation therapy led to oversecretion of pancreatic insulin, which is most likely a consequence of insulin resistance.