Probiotics are living microorganisms which provide benefits to the host. They have been demonstrated to be effective and safe depending on the quantity, dose, route of administration and ingredients in a wide range of diseases such as intestinal inflammation or infection, ischemic heart diseases, urogenital infections, respiratory diseases and protective and treatment role against cancer. Most of the probiotic products currently available comprise lactic acid bacteria (LAB) that belong to the Lactobacillus and Bifidobacterium. There are different sources of probiotic like dairy products, fermented milk, kefir, kimchi, kombucha, kiom-ma, utonga kupsu, noni, soymilk and yogurt. The current paper investigated the major probiotic sources and their safety and efficacy and their mechanisms in the prevention and treatment of several types of cancer including breast, colon, gastric, liver, pancreatic, cervical, oral, lung, leukemia and melanoma cancer at three levels in vitro, animal and clinical studies. Several mechanisms are suggested for prophylactic and antitumor functions of probiotics including production of short chain fatty acids, alteration of colonic motility and transit time, alteration of differentiation process in tumor cells, anticarcinogenic effects, antimutagenic properties, modulation of inflammatory response, inhibition of the bacteria that convert pro-carcinogens to carcinogens, alteration of tumor gene expressions, decrease of intestinal pH to diminish microbial activity, antioxidant activity, modulation of gut microbiota, antiproliferative and apoptotic effects, antiangiogenesis, enhancement of barrier function, their interference in the enterohepatic cycle of estrogen. Several clinical trials revealed probiotics efficacy against prevent of post-operative complications and chemotherapy and radiation therapy related toxicity such as diarrhea and inflammation. However, numerous studies revealed that probiotics had either no or positive influences in associated with safety results like infection and mortality. Nevertheless, more clinical trial studies are essential to recognize the potential strains, dosages and administration regimes with highest efficacy and safety as an adjuvant therapy for cancer treatment for particular types and stages of cancer.