Viale G et al. – Low levels of estrogen receptor (ER) and progesterone receptor (PgR) are predictive of the benefit of adding chemotherapy to endocrine therapy; low PgR may further predict benefit in pre- and perimenopausal but not postmenopausal pts with ER-expressing tumors Methods
Immunohistochemical study to centrally assess ER and PgR and investigate predictive value for benefit of chemoendocrine compared with endocrine adjuvant therapy alone in 2 randomized clinical trials for node-negative breast cancer
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 pts
Trial IX compared 3 cycles of CMF followed by tamoxifen for 5 yr versus tamoxifen alone in postmenopausal pts
Review of 883 (83%) of 1,063 pts on Trial VIII and 1,365 (82%) of 1,669 on Trial IX for immunohistochemical determination of ER and PgR
Subpopulation treatment effect pattern plot to compare disease-free survival (DFS)
Results
Both receptors showed bimodal distribution, most showing no staining (receptor absent) and most remainder showed a high percentage of stained cells
Chemoendocrine therapy yielded DFS superior to endocrine therapy alone in receptor-absent tumors and in some cases of low levels of receptor expression
Among pts with ER-expressing tumors, additional prediction of benefit was suggested in absent or low PgR in Trial VIII but not in Trial IX
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