Primary breast cancer is breast cancer that has not spread beyond the breast or the lymph nodes (glands) under the arm.
Breast cancer is not one single disease. There are several types of breast cancer, all of which can be found at different stages of development and grow at different rates.
Breast cancer that has the potential to spread to other areas of the body is described as invasive breast cancer. This does not mean the cancer has spread to another part of the body but that it has the potential to. Treatments are aimed at reducing the risk of this happening.
People who have breast cancer in one breast are at slightly higher risk of developing a new primary breast cancer. This may happen either in the same breast after breast-conserving surgery or, more likely, in the opposite breast, and is called a second primary diagnosis.
Types of primary breast cancer
Breasts are made up of lobules (milk-producing glands) and ducts (tubes that carry milk to the nipple), which are surrounded by glandular, fibrous and fatty tissue. Breast cancer starts when the cells in the breast begin to divide and grow in an abnormal way.
There are different types of breast cancer and it is important that your doctors have an accurate diagnosis so they can plan the most appropriate treatment for you.
Ductal carcinoma in situ (DCIS) is early breast cancer, sometimes described as intraductal or non-invasive cancer. This means that cancer cells have developed inside the milk ducts, but remain entirely in-situ (in their place of origin) because they have not yet developed the ability to spread outside of these ducts, either within the breast or elsewhere in the body. Both men and women can develop DCIS.
If DCIS is left untreated, the cells may become invasive and develop the ability to spread from the ducts into the surrounding breast tissue and beyond. The type, size and grade of the DCIS can help predict if it will become invasive but currently there is no way of knowing for certain in each individual case.
Invasive primary breast cancer is breast cancer that has the potential to spread from the breast to other parts of the body. The most common type of invasive breast cancer is invasive breast cancer of no special type (sometimes called invasive ductal cancer). This accounts for most breast cancer diagnoses, but there are many other less common special types.
Special type means when the cells are looked at under a microscope they have features that class them as a particular type of cancer. Some types of invasive breast cancer are outlined below.
Invasive ductal breast cancer/Invasive breast cancer of no special type
You may see no special type invasive breast cancer – written as NST or NOS (not otherwise specified). It’s also referred to as invasive ductal breast cancer. Invasive breast cancer of no special type is the most common breast cancer in both women and men and accounts for about 75% of all breast cancers.
Invasive lobular breast cancer
Invasive lobular breast cancer is the second most common invasive breast cancer accounting for about 10-15% of all breast cancers. It occurs when the cancer cells spread outside the lobules and into the breast tissue around them.
Cribriform breast cancer
About 4% of invasive breast cancers have a cribriform part. It’s often mixed with tubular breast cancer. Under the microscope there are distinct holes between the cancer cells, making it look a bit like a sieve.
Inflammatory breast cancer
Inflammatory breast cancer is a fast growing type of breast cancer which accounts for between 1-4% of all breast cancers. The symptoms of inflammatory breast cancer are also common symptoms of breast infections.
Inflammatory breast cancer gets its name because the skin of the breast develops a red inflamed appearance and may feel warm and tender to the touch. The skin may also appear pitted like the skin of an orange. The redness and swelling (oedema) is caused by cancer cells blocking tiny channels called lymph channels in the breast tissue.
Malignant phyllodes tumour
Malignant phyllodes tumours account for less than 1% of all breast cancers. There are two other types of phyllodes tumour called benign (not cancer) and borderline malignant. They are put into these three categories, according to what they look like under a microscope.
Medullary breast cancer
Medullary breast cancer accounts for around 3-5% of all breast cancers. This type of breast cancer usually has a clear, well defined border between the cancer and the surrounding breast tissue – a feature which pathologists use to help distinguish it from other types of breast cancer. It’s more common in women who inherit a faulty copy of the BRCA1 gene.
Metaplastic breast cancer
Metaplastic breast cancer accounts for about 1% of invasive breast cancers. In this type of breast cancer the cells have changed (transformed) from one cell type into another.
Metaplastic breast cancer is treated in the same way as other types of invasive breast cancer although is more likely to be triple negative.
Mucinous breast cancer
Mucinous (also known as colloid) breast cancer is so called because when it is looked at under a microscope, the cells look like they are surrounded by mucous. It’s common to see mucinous cancer mixed with other types of breast cancer, such as invasive breast cancer of no special type. Pure mucinous breast cancer (when no other type of breast cancer is present) accounts for about 2% of all breast cancers.
Paget’s disease of the breast
Paget’s disease of the breast is an uncommon condition which is often noticed by changes to the nipple such as a red, scaly rash which can feel itchy or painful. The nipple may also become inverted. It occurs in less than 5% of all people with breast cancer.
Approximately half of people with Paget’s disease will have an underlying breast lump, which is likely to be an invasive breast cancer. Where there is no lump, most people will have non-invasive or in-situ cancer known as ductal carcinoma in situ (DCIS) somewhere in the breast.
Papillary breast cancer
This type of breast cancer accounts for less than 1% of all breast cancers. Under the microscope the breast cancer cells are in a pattern that looks a bit like the shape of a fern. It is common to see DCIS alongside papillary breast cancer.
Tubular breast cancer
Tubular breast cancer accounts for between 5 and 10% of all breast cancers. It is called tubular breast cancer because the cells look tube-like when they are examined under a microscope.
Triple negative breast cancer
Some breast cancers are referred to as triple negative. This means the breast cancer is oestrogen receptor negative, progesterone receptor negative and HER2 receptor negative which is why it’s called ‘triple negative’ breast cancer. Around 15-20% of people with breast cancer test negative for all three of these receptors. Special and non-special types of breast cancer can be triple negative.