Pak-Sian Dong is a fermented vegetable product of Thailand prepared from aerial parts of Pak-Sian (Gynandropsis pentaphylla DC.). Lactobacillus plantarum KK518 was isolated from Pak-Sian Dong and already assessed for its probiotic attributes. The aim of this work was to determine the untapped cytotoxic effects of L. plantarum KK518 extract against HepG2 (liver cancer), MCF-7 (breast cancer) and HeLa (cervical cancer) cells. The bacterial extracts were prepared from whole cultures; containing cells and broths using ethyl acetate as extracting solvent and the dried extracts were redissolved in ethanol before use. Cytotoxic, antiproliferative and antimigratory effects of the bacterial extracts on three types of cancer cells were determined using 3-(4, 5-dimethylthiazolyl-2)-2, 5-diphenyltetra zolium bromide (MTT) assay, clonogenic formation and wound healing assays, respectively. L. plantarum KK518 extract showed the highest cytotoxicity at 90.88% at 1,000 μg/mL against HeLa cells (IC50 of 371.97 μg/mL) over 48 h of exposure. Anti-colony formation test showed that the bacterial extracts at 600, 800 and 1,000 μg/mL over 48 h led to a complete inhibition of colony formation of HeLa cells; however the highest IC50 of 418.52 μg/mL was found in HepG2 cells suggesting that HepG2 was least affected by bacterial extract. Likewise, HepG2 cells seemed to be most resistant to antimigratory effects as observed by highest relative area of the wound at most time intervals and most extract concentrations. L. plantarum KK518 offers a potential use as a bio-therapeutic with chemopreventive effects against cervical, breast and liver cancers.