This study assessed the anticancer activity of boron-containing and structurally diverse small molecules in 4T1 breast cancer andCaco-2 colon adenocarcinoma cells. Initial screening showed that five boronic acids lacked significant cytotoxicity, underscor-ing the structural specificity required for boron-mediated bioactivity. Similarly, reference compounds, including fumaric acid,caffeic acid, ferulic acid, dimethyl malonate and N- (tert-butoxycarbonyl)-L-alanine, showed no cytotoxic effect under identicalconditions. Among the tested agents, 1-acetyl- 4- (4-hydroxyphenyl)piperazine (1A4HP) displayed the most potent cytotoxicity,with IC50 values of 149.7 μM in 4T1 and 825 μM in Caco-2 cells. For comparison, the clinically investigated antimetastatic agenttasquinimod showed moderate activity in 4T1 cells (IC50 = 180.7 μM), serving as a pharmacological benchmark. Mechanisticassays revealed that 1A4HP induced apoptosis and significantly impaired 4T1 cell migration, suggesting combined antiprolif-erative and antimetastatic effects. Computational analyses further supported 1A4HP’s drug-like potential by predicting favour-able physicochemical properties, including balanced lipophilicity and high solubility. Molecular docking studies indicated astrong binding affinity to oestrogen receptor alpha (ERα), surpassing that of tamoxifen. Notably, despite 4T1’s ER-negative status,1A4HP suppressed cell growth, suggesting possible ER-independent or off-target mechanisms, similar to tamoxifen’s secondaryeffects. Collectively, these results identify 1A4HP as a promising lead compound for further exploration in breast cancers.