Cancer is usually diagnosed by an expert that examines cell or tissue samples under a microscope. If doctors are not sure if the lumps are cancerous or not, they may take a biopsy, taking a piece of the lump, as a sample to use for testing.
When diagnosing cancers, the doctor will determine what stage the cancer is in. There are 4 stages with 1 being the least severe and 4 being that cancer has spread to other parts of the body such as bones or organs.