These extra cells can form a mass called a tumor.

When these extra cells form a mass, it is called a tumor.

These cells form part of the immune system and help to prevent the body from getting diseases.

The extra cells may form a mass of tissue called a tumor.

These cells form the hair in the root and then grow through the skin surface taking any substances with them.

These extra cells grow together and form masses, called tumors.

The cells can form any tissue of the body except the placenta.

Only infrequently does this result in a cell forming more than one hair.

When this happens, these cells do not die but form a mass of tissue called a tumor.

Normal cells can form blood vessels that help cancers to grow.