Malignant neoplasms are cancerous, while benign ones are not. Benign tumors remain in one place, unlike malignant ones, which can spread from the primary site to almost any part of the body, explains MedlinePlus.
Malignancy means that a tumor has a medium to high chance of spreading to other tissues and organs. This occurs when tumor cells move through the lymphatic system or when they spread through the blood, according to Cleveland Clinic. Once in the lymph or blood, tumor cells can be carried to almost any part of the body, which explains how melanoma metastasizes to the brain and causes secondary brain cancer, explains the National Center for Biotechnology Information.
More than 100 types of cancer exist; many are difficult to diagnose, and some are often found late. Diagnosis usually begins with a thorough clinical history and a physical exam. If cancer is suspected, a doctor may order lab tests of the organ system in question. For example, if a person's symptoms include changing bowel habits and rectal bleeding, the doctor may suspect colorectal cancer and order a colonoscopy to check for polyps and any other colonic abnormalities. This is an important screening test recommended for everyone after a certain age, even without the suspicion of cancer, explains WebMD.