The appropriate course of treatment for cancer will depend on the origin of the disease and whether it has spread, which will help your cancer care team select the most effective patient pathway and planning processes.
Everything from cancer origin, type, location, extent, any previous treatments and the individual patient’s overall health are all taken into account, with radiotherapy not automatically indicated for every primary or secondary cancer.
Primary cancers originate at a specific site, while a secondary tumour represents cancer that has spread from one site to another (known as metastasis).
To understand why, it is important to understand the differences between primary and secondary cancer treatment, how this differs from the staging system used to classify certain types of cancer, and how your cancer team will manage treatment.
What Is Primary Cancer?
A primary cancer is a cancer that originates in the tissue or organ where it first develops. The term ‘primary’ can also be used in diagnostic reports and clinical discussions when it is necessary to distinguish the origin from metastatic disease.
What Is Secondary Cancer?
A secondary cancer is a cancer that has spread from its original site to another part of the body, commonly through the blood or lymphatic system.
For example, if the breast cancer tumour from the example above spread to the liver, it would not be considered a liver cancer, but breast cancer that has metastasised to the liver or liver metastases from breast cancer.
The metastatic cells retain the characteristics of the original breast cancer.
This is a vitally important distinction, as identifying the primary cancer helps clinicians select an appropriate treatment strategy.
Are Second Cancers The Same As Secondary Cancers?
No, a second cancer (or second primary cancer) is a new primary cancer that has emerged in the body, rather than a metastasis from the original cancer.
This can be confusing at times, as it is possible to have, for example, a secondary breast cancer that has spread to another part of the body, as well as a second breast cancer that has emerged as a lump in the other breast.
Can You Have A Secondary Tumour Without A Primary Tumour?
Metastatic cancer can be diagnosed even when the primary site cannot be found or identified, rather than it being absent.
This is typically known as a cancer of unknown primary (CUP), referring to confirmed cancer in which the primary site remains unidentified after appropriate diagnostic evaluation.
According to Cancer Research UK, two per cent of cancer diagnoses each year in the UK involve a CUP, with 60 per cent of cases occurring in people aged 74 or older.
Primary tumours may go unidentified because:
- The secondary cancer has grown quickly
- Very small cancers may not cause symptoms or appear on scans
- Your immune system may have successfully attacked the original cancer, while the secondary cancer continues to grow
Is Secondary Cancer Always More Serious Than Primary Cancer?
The term ‘secondary cancer’ generally refers to metastatic cancer, which is different to advanced cancer and Stage IV diseases.
Prognosis will vary according to the cancer type, the extent of the spread, tumour biology and patient response to treatment.
Treatment may control metastatic cancer, relieve symptoms and sometimes achieve long-term remission. Curative treatment may be possible in selected cases, depending on the cancer type and extent of the disease.
Is Secondary Cancer The Same As Advanced Cancer?
Advanced cancer can include locally advanced disease without distant metastasis, while secondary cancer refers to metastatic spread.
Advanced cancer may require treatment aimed at cure, disease control or symptom management, depending on the individual diagnosis.
Some locally advanced cancers remain confined to the original region, while selected patients with limited metastatic disease may be eligible for potentially curative treatment.
