Abstract
BACKGROUND: In a significant proportion of metastatic breast cancer (MBC) patients whose tumour has progressed within 6 months of endocrine therapy (de novo resistance), it is generally believed that the chance of achieving clinical benefit (CB) with further endocrine therapy is minimal. METHODS: Data was retrieved from a prospectively updated database of metastatic breast cancer. Relevant data was exported to SPSS software for statistical analysis. RESULTS: In oestrogen receptor (ER) positive MBC patients with assessable disease, CB was achieved in 159 (71.3%) (1st line) patients. When these patients were put on further endocrine therapy, the CB rates were 63.2% (on 2nd line), 46.1% (on 3rd line) and 20% (on 4th line) with a median duration of response (DOR) in those with CB of 22, 12, 11 and 15 months respectively. The remaining 64 (28.7%) patients had de novo resistance on 1st line endocrine therapy. Seventeen of these patients were treated with further endocrine therapy. The CB rates were 29.4% (on 2nd line) and 22.2% (on 3rd line) with a median DOR in those with CB of 22.7 months and 14 months respectively. CONCLUSION: The chance of further endocrine response continues to decrease with each line of therapy, yet CB is still seen with reasonable duration even with a 4th line agent. In addition, further endocrine response, with long duration, can be seen in a significant proportion of patients who have developed de novo resistance to 1st line endocrine therapy. The use of further endocrine therapy should not be excluded under these circumstances.