Invasive and non-invasive
Breast cancers can be classified as invasive or non-invasive, reflecting whether cancer cells have started to grow into other tissues.
Non-invasive cancer, also known as carcinoma in situ, stays within the tissue where it first appears. Ductal carcinoma in situ (DCIS) is cancer which has not spread into the breast tissue surrounding the ducts. If left untreated, however, it can spread.5,6
Lobular carcinoma in situ (LCIS) or lobular neoplasia is not a cancer, and most women with LCIS will not develop breast cancer. However, cell abnormalities indicate a small increased risk of developing invasive breast cancer so management can include regular monitoring and hormone therapy to reduce the risk of breast cancer developing.
Surgery to remove the breast (mastectomy) may be recommended if the LCIS is ‘pleomorphic’, where cells look more varied than in usual LCIS.7
The most common breast cancer is invasive breast cancer of no special type (NST), accounting for around 70 per cent of invasive breast cancers. The ‘NST’ term is used as the cancerous cells have no special features when viewed under a microscope. It used to be called invasive ductal carcinoma as cancerous cells grow through the epithelial cells lining milk ducts into neighbouring tissue.6,8
Around 15 per cent of invasive breast cancers are classed as invasive lobular breast cancer where cancerous cells in the lobules are growing into other breast tissue.6
Inflammatory breast cancer (1-5 per cent of invasive breast cancer cases) arises from cancer cells blocking lymph channels in breast tissue and the skin. This can cause the skin to look red and inflamed.6
Paget’s disease of the breast (1-4 per cent of breast cancers) appears as an eczema or psoriasis-like skin condition on the nipple/areola. About half of people will also have a lump under the affected area which is an invasive breast cancer in 90 per cent of cases, although invasive breast cancer can also be present with no lump.6,7