If you are diagnosed with cancer, one of the first questions you may ask is “How bad is it?” To answer this question, doctors often refer to the “stage” of the cancer. Most cancers are staged using the TNM system. In this system, T refers to the primary tumor; N refers to lymph nodes nearby that could be affected by cancer; and M refers to metastasis, or the spread of cancer cells to other body parts.

Diagnostic tests help measure each of these aspects of cancer and give it a number. Your medical team then uses this information to pinpoint the best way to fight the cancer. Detailed TNM reports are great for doctors, but can be confusing to patients and families. That’s why most cancer specialists use a four-stage scale to describe the TNM findings to patients. Here’s a quick guide to these stages:

Stage 0: Abnormal cells that could become cancerous are present, but they have not spread to nearby tissue.

Stages I, II and III: Cancer cells are present. A higher number means the cancer is more advanced. Stage 1 cancers are the most easily treated.

Stage IV: The cancer has spread from its original site to other parts of the body. These cancers are challenging to treat.

In some cases, cancer is further staged into subgroups based on the location of the tumor or its characteristics. Not all cancers are staged with the TNM system. Blood cancers, for example, are evaluated with other methods. While cancer staging is important, it doesn’t predict outcomes. Personal health, treatment choices, and other factors also impact individual results.

If you have questions, call askSARAH, a dedicated phone line where nurses answer your cancer questions, provided by Sarah Cannon, the Cancer Institute of HCA Healthcare.