Stages of Cancer

Every year about 20 million people in the world receive a cancer diagnosis. At this overwhelming, and often scary time, a patient usually learns their cancer’s stage, which is typically a number ranging from 1 to 4. While staging is designed partly to help patients better understand what they are facing, extracting this information from a simple number can be confusing and less than straightforward.

So what do cancer stages mean?

To understand stage numbers, we first need to unpack the three variables that inform it. Doctors utilise a system which uses the letters T, N and M to describe a tumour’s size, its presence in the immune system’s lymph nodes, and whether it has metastasised or spread, to other organs. Arriving at this letter staging takes thorough investigation- the physician will consider a person’s symptoms and overall health and may sample, or biopsy, cancerous tissue, order medical scans and analyse blood tests.

The T designation is usually a number between 1 and 4 and is, in most cases, based on the tumour size. However, each type of cancer has its own T staging criteria. For example, 5 cm wide tumours are labelled T3 in oral cancers but T2 in breast cancers. Some cancers use other staging criteria, like oesophageal cancers, which are stages based on how deeply the tumour invades the layers of tissue.

To assign an N stage, doctors evaluate the lymph nodes through biopsies and imaging. Cancer cells tend to break off from the initial tumour and spread. They often travel through the lymphatic system- a network of vessels and nodes, which filter waste and harbour cells that help fight infection. Cancer that spreads to larger, more distant, to a greater number of lymph nodes typically files into higher N stages.

M staging involves a more threatening category of cancers spread- when diseased cells scatter and then settle on other organs or bones. Historically, this stage has been a matter of just “yes” or “no” because once a cancer has metastasised, it’s considered to be much more lethal. However, advances in treatment have recently prompted the medical community to rethink the M stage as a continuum. Doctors now consider the number of organs in which the cancer has spread, as well as the abundance and the characteristics of the metastatic tumours.

All sorts of combinations of T, N and M are possible, and one letter doesn’t always follow the other. For example, some of the head and neck cancers will test positive in the lymph nodes N1 with no clear initial tumour or T0. So how do these three variables inform of a cancer’s stage number?

Each TNM combination correlates to a different overall stage, ordered by how difficult the cancer is to treat. This sorting is rigidly defined for each type of cancer, based on generations of research looking at how cancers with different spread and characteristics tend to behave. Importantly, what a certain overall stage means varies from cancer to cancer. For example, a T3N1M0 combination for breast cancer is considered stage 3 and carries an 85% five-year survival rate. Pancreatic cancer with this same TNM combination, however, is sorted to stage 2, and yet is more difficult to treat with a 15% survival rate.

The system is intricate and ever-changing. For instance, someone with stage 4 throat cancer in 2017, might be considered stage 1 just one year later. Cancer didn’t improve, the staging system did. Experts realised a subset of these advanced cancers responded to existing treatment better than others, so their staging was downgraded. Similar discoveries and advancements in the genetic testing of tumours are redefining staging in breast, prostate and gynaecological cancers. Meanwhile, breakthroughs in therapies can change things seemingly overnight. Many cancers one considered near impossible to treat are now met with high rates of remission. And thanks to improvements in screenings more and more cancers are being discovered at early stages. So while many will deal with the reality of cancer, either for themselves or through the diagnosis of a loved one, these advances offer better treatments, more targeted cures, and greater hopes for the years to come.