Immunoblotting analysis did not detect any appreciable levels of Stat3 or Src in EGFR immunecomplex or of Src or EGFR in Stat3 immunoprecipitate from the nuclear extracts prepared from human breast cancer, MDA-MB-231 and the human non-small cell lung cancer, A549 lines (Fig. S1C), suggesting a minimal possibility of the existence of a constitutive nuclear EGFR, Src, Stat3 complex in the two cancer cell types. Here, STAT3 is linked to cancer.