What’s the difference between a tumour and cancer?

The terms tumour and cancer can refer to different types of lumps and bumps. But the terms are often confused and misused – by the general public and even health professionals.

For instance, doctors can use euphemisms such as tumour, mass, lesion or spot when they really mean cancer.

So what’s the difference between a tumour and cancer? And why is it important to use the right terms?

What’s a tumour?

The Oxford dictionary defines a tumour as “any abnormal swelling in or on a part of the body”. They develop in nearly any part, including fat, muscle, bone, nerves and glands.

But not all tumours are cancer, and not all cancers are tumours.

Tumours can be “benign” (not cancer) or “malignant” (cancer).

Some benign tumours are harmless and don’t need treatment. These include lipomas (deposits of fat cells under the skin) or haemangiomas (an overgrowth of blood vessels often looking like reddish-purple birthmarks).

Other benign tumours can cause problems due to their location. These include uterine fibroids, which can cause heavy menstrual bleeding, and benign pituitary adenomas, which can over-produce hormones. Even though these tumours are not cancer, they can be dangerous and doctors sometimes advise surgery to remove them.

What’s cancer?

Cancer develops when normal cells acquire genetic changes, called mutations, that allow them to escape the body’s normal “checks and balances”.

Several hallmarks of cancer were defined more than 25 years ago and include uncontrolled growth and avoiding immune destruction.

Importantly, cancer cells can invade surrounding structures (known as invasion) and spread to other sites (metastasis). These are the key features that distinguish malignant tumours (cancer) from benign ones (not cancer).

Cancers in solid organs – such as the breast, skin or lung – are sometimes called malignant tumours because they form masses. But not all cancers form masses. Blood cancers, such as leukaemia, usually do not.

Read more: How does cancer spread to other parts of the body?

How are they detected?

Both tumours and cancers can cause lumps and bumps, either detected by the patient (Doc, what’s this lump?) or during investigation for a symptom (Doc, I can’t swallow).

Symptoms differ depending on where the tumour (both benign and malignant) is and what types of cells it is made of. For example, tumours in the gastrointestinal tract (oesophagus, stomach, bowel) can cause symptoms because the mass starts to obstruct the digestive tract.

Imaging such as ultrasound, CT or MRI might be needed to investigate further. The tissue may also be sampled (via a needle or surgery) then a pathologist can look at the sample under the microscope to determine the cell type to determine whether it’s benign or malignant.

How are they managed?

Management can be similar, such as cutting out a benign meningioma (brain tumour) or a malignant basal cell carcinoma (skin cancer).

Management can also be very different. Malignant tumours (cancer) have the potential to spread, and at advanced stages are associated with increased risk of death. So managing cancer is often more time-sensitive and complex.

Treatment for some malignant tumours involves a combination of surgery, radiotherapy and/or systemic treatment, such as chemotherapy, which affects the whole body.

Why it’s important to get the words right

Misusing the words cancer and tumour can be confusing and misleading. This may be because the word “cancer” carries a stigma of sickness and death, even though many cancers have a good outlook.

When talking to patients, it’s important for doctors to “get it right”. Less than half of patients understand that a doctor means cancer if they use euphemisms such as tumour, mass, lesion or spot.

In fact, any type of ambiguous language doctors use when communicating with patients about cancer can increase confusion.

In a nutshell

The terms tumour and cancer are not interchangeable. Solid cancers are tumours and malignant tumours are cancers.

But not all tumours are malignant, and not all cancers are solid.