PCNA and neoplasm: Quantitative analyses of nuclear ER and PCNA expression in Bx2–Bx4 as a function of distance to collagen I-rich tumor nest boundaries showed that cells expressing higher levels of ER and PCNA were closest to these boundaries and other stromal compositions (Bx2: mean ER intensity at 0–25 μm from collagen I = 780, 50–75 μm = 463, p < 0.001; Bx3: 0–25 μm = 1,058, 50–75 μm = 600, p < 0.001; Bx4: 0–25 μm = 1687, 50–75 μm = 1,105, p < 0.001.