A malignant bone tumor arising from remnants of the fetal notochord. Although it can occur at all ages, it is more frequently seen in middle-aged adults. Most frequent sites of involvement are: sacrococcygeal area, spheno-occipital area, and the cervico-thoraco-lumbar spine. Microscopically, chordomas are composed of cells that form cords and lobules, separated by mucoid intercellular tissue. Some of the cells are large (physaliphorous) and have vacuolated cytoplasm and prominent vesicular nuclei. Other tumor cells are small with small nuclei, without visible nucleoli. Chordomas tend to recur and may metastasize. The most common sites of metastasis are skin and bone. -- 2004