According to the National Cancer Institute, the primary difference between benign and malignant tumors is that malignant tumors are cancerous, while benign tumors are not. Only malignant tumors are able to spread to nearby tissue, enter the bloodstream and expand to other areas.
Stanford Medicine explains that benign tumors are typically surgically removed. Once they are removed, they do not re-grow. However, MedlinePlus acknowledges that a benign tumor has the potential to be harmful. Sometimes the location of the tumor causes it to apply excessive pressure to an important organ.
All tumors, benign and malignant, occur due to abnormal cell growth, indicates MedlinePlus. Old cells do not die, and unnecessary new cells form. If these cells accumulate in a mass, it is a tumor.