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[Criteria of measuring mdr-1 gene expression level in breast cancer by RT-PCR].

OBJECTIVE
To formulate criteria of judjing multidrug resistance gene(mdr-1 gene) expression level and to provide basis for predicting chemotherapy response and prognosis.


METHODS
Using reverse transcription-polymerase chain reaction (RT-PCR) assay, the expression of mdr-1 gene in 82 breast cancer samples was detected. The data were treated by statistic analysis system (SAS)-singlevariate analysis.


RESULTS
The level of mdr-1 gene expression clearly deviated from normal to right distribution (P < 0.0001), and thus might be divided by quantiles P50(mdr-1/beta 2-MG = 0.2) and P75 (mdr-1/beta 2-MG = 0.6), which were taken as the criteria for comparing 56 patients' chemosensitivity to ADM, VDS, VCR in vitro and 32 relapsed metastatic patients' chemotherapy response in vivo, seperately. When mdr-1/beta 2-MG < 0.2, the ratio of coincidence was lower between expression of mdr-1 and drug resistance in vitro and in vivo; When mdr-1/beta 2-MG > or = 0.2-< 0.6, the ratio of coincidence elevated slightly, but in 30%-50% of the cases drug resistance in vitro and in vivo did not correlate. When mdr-1/beta 2-MG > or = 0.6, the ratio of coincidence elevated significantly. According to the above-mentioned results, criteria of evaluating mdr-1 gene expression level was formulated: the mdr-1/beta 2-MG ratio < 0.2(P50) was considered as negative expression, the ratio > or = 0.2-< 0.6(P75) was weakly positive expression, > or = 0.6 was strongly positive expression.


CONCLUSIONS
The criteria of mdr-1 gene expression may reflect objectively drug resistance in vitro and chemotherapy response in vivo. The method may also be applicable to other tumours.