Cancer: Malignant tumour cells are cancers. They invade neighbouring tissues and spread to different parts of the body in the blood where they form secondary tumours.

The idea

A malignant tumour is a cancer. Its cells divide uncontrollably and do not stay contained. They invade neighbouring tissues, breaking into them and damaging their normal function. Malignant cells can also enter the blood or lymphatic system and travel to other parts of the body. Where they settle, they divide again to form secondary tumours, often called metastases. This spread is why cancers can affect organs far from where they started.

For example: A malignant tumour in the lung can release cells that travel in the blood and form a secondary tumour in the liver or brain.

What earns the marks

• Malignant tumour cells are cancer cells that divide in an uncontrolled way.
• Malignant cells can enter the blood and travel to different parts of the body.
• Where they settle, they form secondary tumours, also known as metastases.
• The ability to invade and spread distinguishes malignant tumours from benign tumours.

Common mistakes and how to put them right

• Saying malignant cells spread through the air.

  Put it right: They spread in the blood, and also via the lymphatic system, to form secondary tumours.

• Confusing a secondary tumour with a new, unrelated cancer.

  Put it right: A secondary tumour is formed from cells that broke away from the original malignant tumour.

• Stating that malignant tumours stay in one place.

  Put it right: Invasion of neighbouring tissues and spread in the blood are defining features of malignancy.

Exam tips

• Use the terms 'invade' and 'secondary tumours' accurately when describing malignant tumours.
• Link the spread specifically to the blood when explaining how cells reach distant organs.
• When comparing tumours, state clearly that malignant cells invade and spread whereas benign cells do not.