What Is Cancer Stage? How Can You Tell Whether a Tumor Is Responding to Treatment?

What Is Cancer Stage and How Is It Determined?

Cancer stage is a classification system used to determine a tumor’s size and extent of spread. It varies according to how large the tumor has grown and whether it has spread through the body. Cancer stage is used to assess treatment choices and a patient’s estimated life expectancy.

Different staging systems may be used for different cancer types. For example, the TNM (Tumor, Lymph Node, Metastasis) system can be used for large bowel (colon and rectal) cancers. In this system, T indicates tumor size, N indicates spread to lymph nodes, and M indicates metastasis (spread). Using this system, cancer stage can range from 0 to 4. Stages are determined by tumor size and spread. For example, stage 0 cancer indicates a small lesion at an initial stage, while stage 4 cancer indicates advanced tumor spread.

T: Tumor size and location.

N: Number of lymph nodes to which the cancer has spread.

M: Metastasis, or cancer spread.

We know that not all metastatic cancers are the same and that the number of sites of spread to other organs also matters. Patients with a single metastasis, also called “oligometastasis,” have been shown to have a better prognosis (disease course) with good treatment planning.

Are the Imaging Tests Sufficient?

Cancer is diagnosed and treatment response measured using radiological imaging techniques. These techniques aim to visualize cancer cells and determine whether they have spread through the body. The most commonly used oncological imaging techniques are ultrasound, mammography, computed tomography, magnetic resonance imaging (MRI) and positron emission tomography (PET).

If you have questions about your cancer’s stage, whether it is responding to treatment or whether it has recurred, you can consult your doctor for more information or seek a second specialist opinion .

You will undergo repeat oncological imaging at intervals throughout treatment. These tests monitor treatment effectiveness and the tumor’s size and spread.

Can I See How Cancer Has Spread in My Body and How It Relates to My Organs?

Imaging tests can generally show how cancer cells have spread through your body and how they affect your organs. Physical examination, overall performance status and blood tests also provide information for the doctor. PET-CT is the most commonly used imaging test to detect cancer spread. These tests are performed to determine how cancer has spread and affects your organs. More recently, liquid biopsy is also being investigated to determine cancer spread, recurrence and response to treatment.

How Can You Tell Whether Cancer Is Responding to Treatment?

During cancer treatment, certain tests are performed to assess its effect. These may measure the number of cancer cells or involve oncological imaging techniques that examine how cancer cells have spread in the body.

Radiological imaging is most commonly used to determine whether solid (organ-based) cancers are responding to treatment. These methods produce images of organs and tissues inside the body. For example, computed tomography, magnetic resonance imaging (MRI) or PET-CT can assess whether a tumor is shrinking with treatment. These tests allow your doctor to evaluate treatment and make changes if needed.

What Is a PET Scan?

PET (positron emission tomography) is a medical imaging technique used to visualize the movement and distribution of certain molecules within the body. During a PET scan, a radioactive tracer is injected into the body. As it moves through the body, it releases radiation through positron emission. A PET scanner detects this radiation and creates an image showing how active certain areas and cells in the body are. PET can be used in the diagnosis and treatment of many different health conditions, including cancer.

PET is a nuclear imaging method that usually shows the metabolic activity of particular cells. It does not provide good anatomical imaging. To make the images obtained with PET more useful, it is combined with computed tomography (CT) or magnetic resonance imaging (MRI).

What Types of PET Scan Are There, and Is Mine Appropriate?

There are many types of PET imaging. The most commonly used include:

• FDG-PET: The most commonly used PET technique. It images how cells in the body use radioactively labeled glucose (a sugar molecule). More metabolically active cells, such as cancer cells, take up more FDG, producing a brighter image at the tumor site. Typical lung, breast and colon cancers are visualized very well with FDG-PET-CT.
• PSMA-PET: Prostate-specific membrane antigen positron emission tomography. This PET technique images the spread and growth of cells in prostate cancer. To determine the spread and growth of tumors in prostate cancer , it uses a radioactive tracer called prostate-specific membrane antigen (PSMA). This tracer is specifically metabolized by prostate cancer cells and detected by the PET scanner, allowing tumor spread and growth to be imaged.
• FAPI-PET: Fibroblast activation protein (FAP) is a molecule produced in excessive amounts by cancer-associated fibroblasts. Radioactive FAP inhibitors (FAPIs) targeting these molecules are used as PET tracers, enabling tumors to be imaged almost at the cellular level. It is particularly valuable in ovarian cancer with peritoneal spread .
• Gallium 68 DOTA-TATE PET: This technique can be used in various cancer types but is most commonly used in neuroendocrine tumors. It can also be used in certain nervous system tumors.
• PET-MRI: Positron emission tomography–magnetic resonance imaging. Conventional FDG-PET-CT does not image the brain and liver well. This method is used when targeting the brain and liver.