SERIAL CYTOLOGICAL ASSAY OF MICRONUCLEUS INDUCTION - A NEW TOOL TO PREDICT HUMAN CANCER RADIOSENSITIVITY

Background and purpose: The micronucleus test, generally done in cultu red tumour cells irradiated in vitro, has not gained wide ge acceptanc e in predicting human cancer radiosensitivity. The purpose of this stu dy was to see if micronucleus assay by serial scrape smear cytology ca n predict oral cancer radiosensitivity. Materials and methods: Forty n ine oral cancer patients given radiotherapy (60 Gy/25 fractions/5 week s) form the study population. Serial scrape smears were taken from the ir tumours before treatment and after delivery of 2, 5, 8 and 12 fract ions, stained by Giemsa and the number of micronucleated cells (MNC) n oted. The patients were grouped to those who developed tumour recurren ce ('Resistant') and those who did not ('Sensitive'), and the pattern of micronucleus induction compared. Results: Both groups of tumours ha d MNC even before treatment, with statistically significant dose-relat ed increase with radiotherapy. The sensitive group had a higher mean i ncrease in MNC count than the resistant group (6.1 times and 3.6 times the pre-treatment value, respectively) and better correlation with do se (r=0.54 vs. 0.43). The increase in MNC count occurred earlier in th e resistant group than in the sensitive, the T-MNC (time for the pre-t reatment value to double) being 3.3 days and 7.6 days, respectively. A lso, the resistant group showed a plateauing of the MNC count which th e sensitive group lacked. Conclusion: The higher MNC induction in the sensitive tumours suggests the usefulness of the assay as a test of ra diosensitivity. The differing patterns of MNC increase suggest that di fferences in proliferation rate is an important cause of tumour failur e. Serial cytological assay of micronucleus induction can identify bot h radiosensitivity and proliferation characteristics of tumours, and t hus may turn out to be a useful test of radiocurability.