Worldwide, breast cancer is the leading type of cancer in women, accounting for 25% of all cases. In 2012 it resulted in 1.68 million cases and 522,000 deaths. It is more common in developed countries and is more than 100 times more common in women than in men. Prostate cancer, also known as carcinoma of the prostate, is the development of cancer in the prostate, a gland in the male reproductive system. Simvastatin, an anti-hyperlipidemic drug shows the anti-cancer activity on hormone dependent carcinomas. Results obtained in vitro have shown that statins can inhibit tumor cell growth. The main challenge in cancer chemotherapy is toxic side-effects induced by chemotherapeutic drugs. Single dose or short-time application will probably causes serious health problems, but the use of biodegradable nano-sized particles for long-term or life-time therapy may produce better therapeutic-effects with less side effects. Increasing the encapsulation efficiency of poorly water-soluble molecules will lead to the development of improved SLN formulations to increase the efficacy and reduce the side-effects of chemotherapeutic drugs for anticancer treatment.