The stage of a cancer is a descriptor (usually numbers I to IV) of how much the cancer has spread.  The stage often takes into account the size of a tumor, how deep it has penetrated, whether it has invaded adjacent organs, how many lymph nodes it has metastasized to (if any), and whether it has spread to distant organs.  Staging of cancer is important because the stage at diagnosis is the most powerful predictor of survival, and treatments are often changed based on the stage.
Cancer staging
Breast cancer laboratory tests
Breast cancer staging
Lymphadenopathy classification
Breast cancer physical examination
Paget's disease of the breast staging
Endometrial cancer staging
Lymphadenopathy physical examination