A benign tumour is not cancer, but it is not always harmless either
Benign sounds reassuring, and in medicine it mainly means one thing: the growth does not invade nearby tissue or spread around the body. Moles and fibroids fit the label. Yet a harmless-sounding lump can still press on nerves, flood the body with hormones, or, trapped inside the skull, threaten life.
What sets these growths apart from cancers is invasiveness. They usually grow more slowly, their cells look fairly normal and specialised, and they often sit inside a fibrous capsule. The rules have exceptions: some benign tumours grow fast or look poorly differentiated, while certain cancers, such as basal-cell carcinoma, rarely spread. Surgery usually removes them for good, and a tumour that keeps coming back can signal that it has turned malignant.
Their danger comes mostly from location and chemistry. Expanding outward as rounded masses, they can squeeze neighbouring structures, blocking ducts, starving tissue of blood or damaging nerves, a problem called mass effect that is worst in tight spaces like the skull, sinuses or airways. Some make hormones: insulinomas can pour out enough insulin to crash blood sugar, and pituitary adenomas can cause acromegaly or Cushing's disease. Vascular tumours may bleed enough to cause anaemia, and skin growths can bring social and psychological strain.
Several inherited conditions show how benign growths arise when tumour suppressor genes fail. In familial adenomatous polyposis, a faulty APC gene lets beta-catenin build up and switch on growth genes, producing colon polyps that become cancer unless removed. Tuberous sclerosis stems from broken TSC1 or TSC2 genes that normally restrain a growth regulator called mTOR. Von Hippel-Lindau disease disrupts how cells respond to low oxygen, triggering blood vessel growth. PTEN mutations underlie Cowden and Proteus syndromes.
Some familiar examples show the range. Lipomas, soft painless lumps of fat cells, affect about 1% of people, appear most often between 40 and 60, and in around 65% of cases involve changes on chromosome 12; removal is usually final. Osteochondromas are cartilage-capped bony projections that stop growing when a bone's growth plates close. The link to cancer is a process: after an initial mutation, a cell multiplies into a usually benign mass, and further mutations in some of its cells can progress it to malignancy.
Source: Benign tumor
