Chemoendocrine compared with endocrine adjuvant therapies for node-negative breast cancer: predictive value of centrally reviewed expression of estrogen and progesterone receptors--International Breast Cancer Study Group.

Purpose
To centrally assess estrogen receptor (ER) and progesterone receptor (PgR) levels by immunohistochemistry
and investigate their predictive value for benefit of chemo-endocrine compared with endocrine
adjuvant therapy alone in two randomized clinical trials for node-negative breast cancer.
Patients and Methods
International Breast Cancer Study Group Trial VIII compared cyclophosphamide, methotrexate,
and fluorouracil (CMF) chemotherapy for 6 cycles followed by endocrine therapy with goserelin
with either modality alone in pre- and perimenopausal patients. Trial IX compared three cycles of
CMF followed by tamoxifen for 5 years versus tamoxifen alone in postmenopausal patients.
Central Pathology Office reviewed 883 (83%) of 1,063 patients on Trial VIII and 1,365 (82%) of
1,669 on Trial IX and determined ER and PgR by immunohistochemistry. Disease-free survival
(DFS) was compared across the spectrum of expression of each receptor using the Subpopulation
Treatment Effect Pattern Plot methodology.
Results
Both receptors displayed a bimodal distribution, with substantial proportions showing no staining
(receptor absent) and most of the remainder showing a high percentage of stained cells.
Chemo-endocrine therapy yielded DFS superior to endocrine therapy alone for patients with
receptor-absent tumors, and in some cases also for those with low levels of receptor expression.
Among patients with ER-expressing tumors, additional prediction of benefit was suggested in
absent or low PgR in Trial VIII but not in Trial IX.
Conclusion
Low levels of ER and PgR are predictive of the benefit of adding chemotherapy to endocrine
therapy. Low PgR may add further prediction among pre- and perimenopausal but not postmenopausal
patients whose tumors express ER.