Figure 3

Kaplan-Meyer curves illustrating the surprising skewed relationship between estrogen receptor alpha (ER) status (immunohistochemistry [IHC] scores) and clinical outcome (disease-free survival [DFS]) in patients (n = 777) with invasive breast cancer treated with adjuvant tamoxifen therapy (reproduced with permission) [7]. Tumors with as few as 1–10% ER-positive cells (IHC score = 3) respond far better than ER-negative tumors (IHC score = 0 and 2 corresponding to none and < 1% ER-positive cells, respectively), and nearly as well as tumors with much higher ER content (IHC score = 4–8 corresponding to > 10% to 100% ER-positive cells). The observation that tumors with a low proportion of ER-positive cells respond almost as well as those with a very high proportion raises important questions about the nature of stem cells that could produce and sustain such biologically diverse but clinically similar populations.