**2. Epidemiology, pathology and prognosis of patients with brain metastasis**

Brain metastases occur in 20% to 40% of cancer patients. Posner and Chernik, from 1970 to 1976 at the Memorial Sloan-Kettering Cancer Center, autopsied 3219 cancer patients. They found that 24% of these patients had intracranial metastases and the 20% had leptomeningeal metastases (Posner and Chernik 1978). Other studies reported similar percentage even if the methodology is slightly different (Baker et al. 1942, Chason et al 1963, Nussbaum 1996). In decreasing frequency, lung cancer, unknown primary, breast, melanoma, renal, and colon cancers are the most common tumors to metastasize to the brain (Pectasides et al. 2006, Norden et al. 2005, Posner and Chernic 1978, Chason et al 1963, Nussbaum et al. 1996).
