CXCL8 and breast carcinoma: When stratifying analyses by tumor immunohistochemistry (Fig. 2), IL-8 was observed to be positively associated with breast cancer risk for ER-negative tumors only (ER-positive: ORper SD increment = 0.95 (0.72–1.24); ER-negative: ORper SD increment = 1.73 (0.98–3.06); P-homogeneityER+ vs ER- = 0.05).