A unified definition of clinical anthracycline resistance breast cancer

The purpose of the study was to determine the response rates (RR) and durat ion to second- and third-line chemotherapy programmes in patients with anth racycline-resistant breast cancer, utilizing Various definitions of anthrac ycline resistance. This was a retrospective analysis performed on 1335 pati ents with metastatic breast cancer who participated in consecutive clinical trials of first line, anthracycline-containing combination chemotherapy (A CCC) at the University of Texas MD Anderson Cancer Center between July 1973 and April 1980. Anthracycline-resistant groups were identified using defin itions of anthracycline resistance found in the literature: progressive dis ease as best response to ACCC (Group 1, n = 56 patients); progressive disea se while receiving ACCC after an intervening response to the drug (Group 2, n = 84); progressive disease within 6 months of last dose of ACCC (Group 3 , n = 233), and progressive disease within 12 months of last dose of ACCC ( Group 4, n = 272). Second- and third-line therapies administered to these p atients included methotrexate, doxorubicin, mitoxantrone, bisantrene, vinbl astine, vindesine, melphalan, mitomycin, cisplatin, etoposide and others, b ut not taxanes. The distribution of patients' characteristics was similar b etween the four groups, as was the use of second- and third-line regimens. Response rate (RR) to second-line chemotherapy were 5% and 7.7% for Group 1 and Group 2 respectively. In contrast, RR to second-line chemotherapy were 21.6% and 15% for Group 3 and 4. The differences in response rate between the combination of Groups 1 and 2 and Groups 3 or 4 were significant (P = 0 .005 and P = 0.04 respectively). These results indicate that strictly defin ed anthracycline resistance as defined in Groups 1 and 2 is associated with resistance to many other cytotoxic drugs. The definitions used in Groups 3 and 4 include many patients with responsive tumours, and a more favourable prognosis. (C) 2000 Cancer Research Campaign.