They can enter the bloodstream or lymphatics. Carried by the flow of blood, these cells set up new colonies, secondary tumours, throughout the body. This process is called metastasis . Of the malignant tumours that are detected early, nine out of ten can be removed before they get a chance to spread. Cells from benign tumours do not spread and they are not invasive - but that does not mean that they are harmless.
Benign tumours cause damage by taking up space and pressing on important organs.
Nine out of ten breast lumps are benign and can be removed by surgery. Each month hormones associated with the woman's menstrual cycle stimulate cells in the breasts to divide. The number of cells in the breasts increase and the breasts swell. Breasts may feel slightly tender in some women as they approach the end of their cycle. When the end of the cycle is reached, some cells die and the breasts become smaller.