Glutathione S-transferase M1 genotype determination
The PCR method described above allowed an internal standard controlled classification of GSTM1-deficient (GSTM1-null genotype) individuals. Of the 92 patients, 57.6% (n = 53) were classified as heritably GSTM1 deficient, and 42.4% (n = 39) were GSTM1-positive genotype. Paired samples of blood and breast tissue were analysed before treatment with primary chemotherapy from the same individual, and GSTM1 genotype was identical for the two samples (Fig. 1). Among the 39 patients with GSTM1-positive genotype, tissue samples obtained before and after treatment were available from 28 cases, allowing RNA extraction and GSTM1 expression using the RT-PCR method. Two of these patients had bilateral lesions, and measurement was determined in the two tumour localizations. Thus, total GSTM1 expression, as measured by the ratio of GSTM1 to β2- microglobulin values, were performed on 30 tumour specimens. GSTM1 RNA signal was detected in all of the tumours analysed before and after treatment. The median GSTM1 expression was 1.38 (range 0.02-23.27) in the untreated tumours, and 1.16 (range 0.01-6.56) in samples obtained after chemotherapy administration.