Even though there are 100 different types of cancer, each one begins in your cells, your body's basic building blocks. When the cell creation process goes awry, abnormal cells are produced that can grow uncontrollably and cause cancer. When excessive cells form, benign or malignant tumors can develop throughout your body. While benign tumors aren't cancerous, malignant ones can invade healthy tissue and spread to other parts of the body, a process called metastasis. Early detection and treatment is key to fighting cancer.