In this section: Unknown Primary Cancer

CANCER of an unknown primary

What do we mean by 'Cancer of an Unknown Primary'? Cancer of Unknown Primary in the head and neck region occurs when the origin of the cancer is unknown, but is found to have spread to the lymph nodes in the neck. If it's not the cancer type you're looking for, please explore the information about other types of Head and Neck Cancers.

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1. What is cancer of unknown primary?

Cancer of Unknown Primary in the head and neck region occurs when the origin of the cancer is unknown, but is found to have spread to the lymph nodes in the neck.

Cancer of Unknown Primary accounts for 3–5% of all head and neck cancers.

Cancer occurs when cells become abnormal and grow uncontrollably. These cells build-up to form a mass (or lump). 

Most cancers that spread to the lymph nodes of the neck come from flat-shaped cells that line areas such as the inside of the mouth, nose and throat. These cancers are called squamous cell cancers (SCC).

Only a minority of cancer cases come from the salivary glands and other structures; another source are skin cancers, where squamous cells are also found.

What are lymph nodes?

Lymph nodes are bean shaped glands in the neck that are part of the immune system’s defence against infection. There are hundreds of lymph nodes in the head and neck area and the majority of these run down the sides of the neck and under the jaw. Lymph nodes are normally difficult to feel because they are soft and small (less than 1 cm). The lymph nodes may become swollen during infection or due to cancer.

Watch a 3D video explainer about Cancer of an Unknown Primary:

2. What causes cancer of the unknown primary?

Doctors often can't explain why a person gets cancer. However, the main causes of head and neck cancers and Cancer of Unknown Primary are:

  • Alcohol and smoking (cigarettes, cigars or pipes) or using ‘smokeless’ tobacco (snuff and chewing tobacco): significantly contribute to the development of head and neck cancer. This is especially true for cancers of the mouth, throat and larynx (voice box). Those who smoke and drink a lot of alcohol are at a much higher risk compared with those who only use either alcohol or smoking alone. Get information about quitting smoking and reducing how much alcohol you drink

  • Infection with HPV (human papillomavirus) may contribute to the development of head and neck cancer, particularly those involving the tonsils or tongue base. The cancers in the tonsil and tongue base are usually small and difficult to detect, but have the ability to spread to enlarged lymph nodes in the neck and account for many cancers of unknown primary.

  • ​Sun exposure contributes to skin cancer, the most common type of cancer in Australia. Patients with skin cancer often have had many primary cancers treated making it difficult to know whether a cancer in a lymph node has come from a skin cancer or not​.

  1. Head and Neck Cancer Australia Resources 
  2. External Links to other Head and Neck Cancer Resources