Introduction
Palpable breast cysts (also known as cystic disease of the breast) are common in women in industrialised countries. Previous studies of the relationship between palpable breast cysts and breast cancer have shown conflicting results, but many have shown an elevated risk. There are two types of breast cyst, defined according to the biochemical properties of the aspirate. Previous studies have suggested that women with type I cysts (characterised by an aspirate with an electrolyte composition similar to that of intracellular fluid) are at an increased risk of breast cancer, compared with women with type II cysts (with an aspirate having an electrolyte composition similar to that of plasma).