EXPRESSION OF MDR1 GENE IN HUMAN BREAST PRIMARY TUMORS AND METASTASES

Expression of mdr1 gene has been evaluated in 34 tumor samples obtaine d from breast cancer patients who were classified according to their t reatment, and clinical follow-up. No gene amplification was found. mdr 1-RNA was never detected in 29 primary breast tumors including 5 sampl es from patients previously treated by 6 courses of 5-fluorouracil, ep irubicin, cyclophosphamide (FEC). On the other hand, mdr1-RNA expressi on was detected in 1 local recurrence and 2 out of 3 metastases, all o f them being treated and exhibiting a poor evolution. A second, untrea ted local recurrence remained negative. Clinical follow-up for 7 to 48 months in patients receiving chemotherapy showed that absence of mdr1 -RNA could not be an accurate factor of satisfactory response to chemo therapy. But, all the patients with detectable mdr1-RNA exhibited a po or evolution and response to treatment. In conclusion, evaluation of m dr1-RNA seemed to be of little interest in primary breast tumors. Howe ver, the concomitant presence of an mdr1-RNA and a metastatic phenotyp e could give a new insight into the relationship between invasive and resistance properties of cancer cells. Such situations would need to b e analyzed very carefully for a better utilization of chemotherapy.