Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. A pelvic tumor is any one of numerous tumors that occur in the pelvis. Within the pelvis, these tumors may involve specific organs, or occupy intra-organ spaces. Tumors of the presacral space and sacral space are most prevalent in children. Tumors occupying specific organs have a more complex natural history. A tumor or tumour is commonly used as a synonym for a neoplasm (a solid or fluid-filled (cystic) lesion that may or may not be formed by an abnormal growth of neoplastic cells) that appears enlarged in size.