Why Cancer Staging Matters
When someone is diagnosed with cancer, one of the first things the medical team needs to determine is the stage of the disease. Staging describes how far the cancer has spread from its original site. It answers critical questions: Is the tumour confined to one organ? Has it reached nearby lymph nodes? Has it spread to distant parts of the body?
These answers directly shape the treatment plan. A cancer that is localised may be treated with surgery alone. One that has spread to regional lymph nodes might need surgery plus radiation or chemotherapy. Widespread disease typically requires systemic treatment. Without accurate staging, treatment decisions are being made with incomplete information.
What Nuclear Medicine Brings to Staging
Nuclear medicine scans are functional imaging studies. Unlike CT scans or MRI, which primarily show the structure and anatomy of organs, nuclear medicine scans reveal how tissues are behaving at a cellular or molecular level. This functional information is what makes them so valuable in cancer staging.
A lymph node that looks normal in size on a CT scan might still harbour cancer cells. A bone that appears structurally intact on an X-ray might already have early metastatic involvement. Nuclear medicine scans can detect these changes before they become structurally visible, often catching disease spread earlier than anatomical imaging alone.
PET CT in Cancer Staging
FDG PET CT is the most widely used nuclear medicine scan for cancer staging. FDG (fluorodeoxyglucose) is a radioactive glucose analogue. Cancer cells, because they are rapidly dividing, consume more glucose than normal cells. When FDG is injected into the bloodstream, it accumulates preferentially in areas of high metabolic activity, including most cancers.
The PET CT scan combines this metabolic information with a CT scan performed simultaneously, giving both functional and anatomical detail in a single study. This combination is powerful for staging because it can:
- Detect the primary tumour and assess its metabolic activity
- Identify cancer in lymph nodes that may appear normal-sized on CT alone
- Find distant metastases in organs, bones, and soft tissues throughout the body
- Reveal unsuspected sites of disease that change the staging and treatment plan
PET CT is commonly used for staging lung cancer, lymphoma, head and neck cancers, oesophageal cancer, colorectal cancer, melanoma, and many other malignancies.
When PET CT Changes the Stage
Studies have shown that PET CT changes the cancer stage assigned by conventional imaging in a meaningful percentage of patients. In some cancers, upstaging (finding more extensive disease than initially thought) occurs in 15 to 30 percent of cases. This means that without PET CT, a significant number of patients might receive treatment that does not match the true extent of their disease.
Conversely, PET CT can also clarify that a suspicious finding on CT is not actually cancer, potentially saving a patient from unnecessary invasive procedures.
Bone Scans
A bone scan (skeletal scintigraphy) is a nuclear medicine study specifically designed to evaluate the skeleton. A radioactive tracer called Tc-99m MDP is injected and accumulates in areas of increased bone turnover, which is a hallmark of bone metastases.
Bone scans are particularly useful in cancers that commonly spread to bone, such as breast cancer, prostate cancer, and lung cancer. They scan the entire skeleton in a single session, making them efficient for surveying all bones at once.
While bone scans are highly sensitive for detecting metastases, they are not highly specific. Arthritis, fractures, and infections can also cause increased tracer uptake. Your doctor interprets the bone scan results alongside your clinical history and other imaging to determine the significance of any findings.
Other Nuclear Medicine Scans Used in Staging
Beyond PET CT and bone scans, several other nuclear medicine studies contribute to staging specific cancers:
- Ga-68 DOTATATE PET CT: Used for staging neuroendocrine tumours, which express somatostatin receptors that this tracer targets.
- PSMA PET CT: Specifically designed for prostate cancer staging and recurrence detection.
- I-131 whole body scan: Used after thyroid cancer surgery to detect residual or metastatic thyroid cancer tissue.
- MIBG scan: Used for neuroblastoma, pheochromocytoma, and paraganglioma staging.
Each of these scans uses a tracer designed to target a specific characteristic of a particular cancer type, providing tailored information for staging that general imaging cannot offer.
How Staging Guides Treatment
The information from nuclear medicine scans feeds directly into treatment planning discussions. These discussions typically happen in a multidisciplinary tumour board, where surgeons, oncologists, radiation oncologists, radiologists, and nuclear medicine physicians review all the data together.
Accurate staging helps the team decide:
- Whether surgery is feasible and likely to be curative
- Whether radiation therapy should be added, and to which areas
- Whether systemic therapy (chemotherapy, immunotherapy, targeted therapy) is needed
- Whether the treatment intent is curative or palliative
Nuclear medicine does not replace other imaging modalities. It works alongside them. The combination of structural detail from CT and MRI with the functional information from nuclear medicine scans provides the most complete picture of a patient’s disease.
Talking to Your Doctor
If you have been diagnosed with cancer and are undergoing staging investigations, ask your oncologist whether nuclear medicine scans are part of your evaluation. The answer depends on the type and suspected stage of your cancer, but these scans are a standard part of staging protocols for many malignancies.
Learn more about the role of nuclear medicine in cancer care on our nuclear oncology page, or browse the full range of imaging studies on our our scans page.