Primary
nasopharyngeal carcinomas (NPCs) may be of various types, including
squamous cell carcinomas,
undifferentiated carcinomas, and lymphoepitheliomas.
Tumor initiation has been linked to the Epstein-Barr virus and, in some geographical regions, to alimentary factors. Possible hereditary components for the appearance of NPCs have not yet been clearly identified. In this study, genetic sensitivity to the genotoxic effects of carcinogenic
xenobiotics as an endogenous risk factor of
tumor initiation was investigated. The single cell
microgel electrophoresis assay was used to quantify chemically-induced DNA damage in lymphocytes of 30 NPC patients and 30 non-
tumor donors. The
xenobiotics investigated were
N'-nitrosodiethylamine,
sodium dichromate, and
nickel sulphate, with
N-methyl-N'-nitro-N-nitrosoguanidine (
MNNG) and
dimethyl sulfoxide (
DMSO) as positive and negative controls, respectively. The extent of
DNA migration in the
solvent control cultures was not significantly different between the two groups (1.2+/-0.5 mean Olive tail moment and standard deviation of 30 individuals for NPC patients; 1.1+/-0.4 for non-
tumor donors). With constant exposure and electrophoretic conditions, genotoxic effects of varying degrees were induced by the different
xenobiotics in
tumor and non-
tumor patients (
nickel sulphate: 7.1+/-2.5 for NPC patients and 5.9+/-1.6 for non-
tumor donors;
sodium dichromate: 18.1+/-5.3 for NPC patients and 16.2+/-5.4 for non-
tumor donors;
MNNG: 47.8+/-13.3 for NPC patients and 52.7+/-13.6 for non-
tumor donors). Only
N'-nitrosodiethylamine proved to induce significantly more
DNA migration in lymphocytes of
tumor patients (9.8+/-3.1) as compared to non-
tumor patients (8.2+/-2.3). Although for
sodium dichromate the degree of
DNA migration did not significantly differ, variability in migration patterns proved to be lower in the
tumor group.
Mutagen sensitivity of NPC patients was shown to be elevated for a selected
xenobiotic, whereas a general elevation of
DNA fragility was not present. Further studies on
mutagen sensitivity as an endogenous risk factor influencing the susceptibility of patients at the time of first diagnosis of
nasopharyngeal carcinomas are warranted.