Selection of primary breast cancer patients for adjuvant endocrine therapy - is oestrogen receptor alone adequate?

Among 834 patients who had primary breast cancer treated by surgery without adjuvant systemic therapy, 363 had relapse treated by endocrine therapy alone. Patients with oestrogen receptor positive tumours (median: 70 vs. 45 months, p < 0.0001) or with non-progression at 6 months of therapy (median: 111 vs. 37 months, p < 0.0001) survived longer than those with oestrogen receptor negative tumours or with disease progression respectively, presumably due to the effect of therapy. On the other hand, the median disease-free interval, uninfluenced by therapy, showed a similar difference: oestrogen receptor positive versus negative = 29 versus 21 months, p < 0.005; non-progression versus progression = 40 versus 19 months, p < 0.0001. Patients with oestrogen receptor-positive tumours and non-progression at 6 months had the longest disease-free interval. The present study has established that there are factors, other than the oestrogen receptor, inherent in the primary tumour as reflected by the disease-free interval, which affect hormone sensitivity. Selection of adjuvant endocrine therapy based on the oestrogen receptor alone would deem inadequate. Further studies to elucidate other possible factors are warranted to refine the use of endocrine therapy, especially in the adjuvant setting when no indication of response is available.