Oncogenotoxicology: A new approach to individual therapy and to the follow-up of patients

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Background: The growing awareness of differences in inter-individual response to radiochemical exposure calls for a new approach in the therapy and follow-up of cancer patients. Results obtained by genotoxicological methods (Bonassi, 2006) showed that surrogate tissue could be used to predict cancer risk. Chromosome aberration (CA) and micronucleus (MN) assay enables:determination of radio- and chemosensitivity level in a patient, adjustment of therapy and detection of chromosomal rearrangements possibly related to the development of secondary cancer using fluorescent in situ hybridization (FISH) Methods: Ten women with breast cancer (BP) and 10 men with oropharinx cancer (OP) were analyzed before, during and after radiotherapy by CA and MN assay. Confounding parameters (age, diagnostics, smoking, drinking) were monitored and matched. Results were compared with 20 matched control subjects. The BP group received an irradiation dose of 60 Gy and the OP group of 62 Gy Results: Before therapy, the OP patients had a significantly higher MN frequency than BP and controls (23.2±4.9‰ versus 6.3±1.6 ‰ and 6.7±3.7‰). On measurements taken 6 and 12 months after the therapy, OP patients continued to have a significantly higher MN frequency than BP patients (60.2±11.4‰ vs. 8.4±2.4‰ and 30.7±4.7‰ vs.5.11±2.5‰, respectively). CA frequency was similar in both groups before therapy (2.5±1.1% in BC and 3.4±1.3% in OP; controls 1.2%). Twelve months after the therapy, the elimination of CA in OP patients was significantly slower than in BC patients (17.7±10.9% vs. 8±5.4%, respectively). As OP patients consumed more than 120 g/day of pure alcohol, it is possible that alcohol could have caused additional genome damage (Maffei, 2002). The highest inter-individual difference in genome damage was observed in BP patients Conclusions: The results show that the CA and MN assay are sensitive methods which can be used to introduce a new concept, oncogenotoxicology, whose goal is to improve the therapy results by evaluating inter-individual differences in response to radiochemical treatment and to improve the evaluation of risk of secondary cancer development. FISH in suspension (Wu, 2005) will allow automation of CA detection, and facilitate a more accurate prospective study of the same population.

No significant financial relationships to disclose.

Alkaline comet assay study with breast cancer patients: evaluation of baseline and chemotherapy-induced DNA damage in non-target cells

The sensitivity of the alkaline comet assay for the evaluation of baseline and treatment-induced DNA damage in white blood cells of breast cancer patients receiving adjuvant chemotherapy according to three conventional anthracycline- and cyclophosphamide-containing protocols was investigated. Additionally, baseline DNA damage in cancer patients was compared with the levels of DNA damage recorded in healthy women. Altogether 30 patients with diagnosed breast cancer and 30 female blood donors with no known familial history of breast cancer participated in the study. Alkaline comet assay was performed according to standard protocol and DNA migration in peripheral blood leukocytes was measured by a computer-based image analysis system. For each subject the frequency of "damaged" cells, i.e., long-tailed nuclei (LTN) with tail length exceeding 95th percentile for the considered parameter among controls, is also reported. Breast cancer patients had significantly increased background levels of DNA damage in their peripheral blood leukocytes as compared to healthy women. Prior to the chemotherapy, a majority of patients showed a statistically significant increase in the number of LTN compared to healthy blood donors. Marked interindividual variations in baseline DNA damage among patients were recorded, some of them related to the disease stage and status. The present study confirmed the alkaline comet assay as a sensitive technique able to detect significantly elevated DNA migration in blood cells of patients already one hour after completion of the first cycle of chemotherapy. Administration of antineoplastic drugs in three chemotherapy protocols studied induced a similar increase of primary DNA damage in nontarget cells. The evaluation of the LTN frequencies indicates the best response to the protocol containing cyclophosphamide, methotrexate and 5-fluorouracil (CMF). Our results point to the significance of simultaneous evaluation of DNA migration and frequency of LTN in the same subject and approved the use of alkaline comet assay as a suitable method for the routine detection of critical DNA lesions produced after administration of antineoplastic drugs in the clinical settings.