Sarcomas and carcinomas are types of malignant tumors that can affect bones. They are derived from different types of cells. Sarcomas are derived from mesodermal (mesenchymal cells) and carcinomas are derived from epithelial types of cells. Sarcomas and carcinomas grow and spread differently. Sarcomas grow like "ball-like" masses and tend to push adjacent structures like arteries, nerves, veins away. The compress adjacent muscles into a pseudocapsule that contains microscopic projections of the tumor referred to as satellite nodules. The local growth of sarcomas like a ball enables resection in most instances. Sarcomas tend to arise primarily (directly) from bone as opposed to spreading to bone from another site. Sarcomas spread most commonly to the lungs. They can also spread to other bones (ie. arise from a bone and spread to other bones) and to the liver. These are the most common sites of spread. Sarcomas rarely spread to lymph nodes. Carcinomas grow in an infiltrative manner and grow through infiltration or invasion of adjacent structures. They more easily invade adjacent nerves, blood vessels and muscles. They do not form a pseudocapsular layer and therefore it is difficult to determine its exact anatomic extent during surgery. This makes it more difficult to remove entirely with surgery. Carcinomas spread to lymph nodes, lungs, bones and many other organs depending on the type of carcinoma. Carcinomas involve bone secondarily, that is by spreading from another site such as the breast to the bone. A patient can have the primary site removed and treated (ie. the breast cancer removed) and years later develop a bone tumor/metastasis from the old breast cancer.