From the 1984 lecture programme:
The body contains many different types of cells, in the blood, skin, brain and elsewhere, all with their own individual properties carrying out their particular functions.
The growth and behaviour of cells is controlled by "factors" which regulate their performance. When this regulation goes astray then a cancer may develop.
Most cancers originate from a single, genetically altered cell which, after accumulating further genetic changes, is then able to spread throughout the body causing the disease we recognise as a malignant cancer.
Any tissue can be affected though some, such as the lung (because of cigarette smoking) or the breast in women, may give rise to a cancer much more often than others.
Major clues to identifying the cancer cell's wayward genes have come from applying genetic engineering techniques to the viruses which we know to cause cancer in animals.
Some human cancers also involve viruses. These, and other new approaches to identifying cancers using antibodies, offer new hope for better understanding and so more easily preventing or treating cancer.