Citations are important for a journal to get impact factor. Impact factor is a measure reflecting the average number of citations to recent articles published in the journal. The impact of the journal is influenced by impact factor, the journals with high impact factor are considered more important than those with lower ones. Impact factor plays a major role for the particular journal. Journal with higher impact factor is considered to be more important than other ones. Impact factor can be calculated as average number of citation divided by recent cited articles published in 2 years. Chordoma is a rare type of cancer that occurs in the bones of the skull base and spine. It is part of a group of malignant bone and soft tissue tumors called sarcomas. Chordomas account for about 3 percent of all bone tumors and about 20 percent of primary spinal tumors. They are the most common tumor of the sacrum and cervical spine. A chordoma tumor usually grows slowly, often without symptoms at first, and then might cause symptoms for years before doctors find it. Chordomas are complicated tumors to treat due to the involvement of critical structures such as the brainstem, spinal cord, and important nerves and arteries. They can also come back, or recur, after treatment — usually in the same place as the first tumor. This is called a local recurrence. In about 30 to 40 percent of patients, the tumor eventually spreads, or metastasizes, to other parts of the body. Chordoma is diagnosed in just one in one million people per year. That means that about 300 patients are diagnosed with chordoma each year in the United States, and about 700 in all of Europe. At any given time, fewer than one in 100,000 people are living with chordoma. Chordoma tumors develop from cells of a tissue called the notochord, which is a structure in an embryo that helps in the development of the spine. The notochord disappears when the fetus is about 8 weeks old, but some notochord cells remain behind in the bones of the spine and skull base. Very rarely, these cells turn into cancer called chordoma. What causes notochord cells to become cancerous in some people is still not fully known, but researchers are working to learn the answer. Chordomas are tumors that can occur anywhere within the spine or the base of the skull. The two most common locations for chordomas are the lower back (sacral area — approximately one-third to one-half of chordomas) and the base of the skull (approximately one-third of chordomas). Chordomas form from remnants of the notochord — embryonic tissue that eventually forms the center of spinal disks. These tumors are considered malignant and may metastasize, though they typically grow slowly. Even slow-growing chordomas can become aggressive and grow quite large locally, putting pressure on or invading into critical parts of the brain or spine, which may cause pain and nerve problems or even be life threatening. Chordomas can press on the spine, brain and nerves as they grow, causing pain and nerve problems specific to the part of the brain or spinal cord where they are located. These symptoms can include tingling, numbness, weakness, lack of bladder or bowel control, sexual dysfunction, vision problems, endocrine problems and swallowing difficulties. If the chordoma has grown very large, you may be able to feel a lump. Treating chordomas can involve extensive surgery, so your doctor will be sure to have a definite diagnosis before planning your individualized treatment.