We found that Chol-siSTAT3 polyplexes (N/P 3) and Chol-DsiSTAT3 polyplexes (N/P 1) suppressed STAT3 mRNA in primary murine 4T1 breast tumors (~30 to 50 mm3) with similar half-maximal ED50 [0.2 ± 0.1 mg Chol-siSTAT3/kg vs. 0.3 ± 0.1 mg Chol-DsiSTAT3/kg] (Figure 3A), maximal suppression [47%] (Figure 3A), and kinetics over 96 h (Figure 3B), whereas Chol-siSTAT3 polyplexes suppressed slightly lower levels of total Stat3 protein [29% vs. 42%] (Figure 4C) and 4T1 tumor growth [rate-based T/C ratio of 11.5% vs. 8.6%] (Figure 4A) after repeated IV administration every other day over 6 days. This evidence concerns the gene STAT3 and neoplasm.