Breast cancer was originally described according to its appearances, so words like scirrhous (meaning woody) were used and still appear in the literature.
More recently, breast cancer has been classified according to its appearances when under the microscope.
Early pathologists classified breast cancers into 'invasive ductal' cancers and 'invasive lobular' cancers, believing that invasive ductal cancers arose in ducts and invasive lobular cancers in the lobules. However, it is now clear that all invasive ductal and invasive lobular cancers arise either in the terminal duct or the lobule. As the terms invasive ductal and lobular are in such common usage and as they have different appearances under the microscope they are still used.
A more logical classification divides tumours into those of 'special' and 'no special' type. Invasive carcinoma of no special type is also commonly referred to as invasive ductal carcinoma. It is the most common type and accounts for up to 85 per cent of all breast cancers.
Special types of tumour have particular microscopic features and these include invasive lobular carcinoma, invasive tubular, cribriform, medullary and mucinous cancers, with other types being uncommon. Many of the special-type cancers have a better prognosis - in other words the patient has a higher chance of survival.
When a cancer is examined under the microscope, it is usually possible to assess how aggressive it is: in other words how far and how fast it is likely to spread. The tumour may be assigned to one of three grades ranging from grade I to grade III in order of seriousness. For instance, a grade I cancer is non-aggressive and unlikely to cause harm. In contrast, grade III tumours are aggressive and likely to cause harm, but can sometimes be controlled with effective treatment.netdoctor.co.uk