The stage of a cancer describes its size and whether it has spread beyond where is started in the body. Knowing the extent of the cancer and the grade helps the doctors to decide on the most appropriate treatment.

Ductal carcinoma in situ (DCIS) is sometimes described as stage 0. DCIS is almost always completely curable with treatment.

The following stages of breast cancer are known as invasive breast cancer:

Stage 1 The tumour measures less than 2cm/1in. The lymph nodes in the armpit are not affected and there are no signs that the cancer has spread elsewhere in the body.

Stage 2 The tumour measures between 2 and 5cm/1–2in, or the lymph nodes in the armpit are affected, or both. However, there are no signs that the cancer has spread further.

Stage 3 The tumour is larger than 5cm/2in and may be attached to surrounding structures such as the muscle or skin. The lymph nodes are usually affected, but there are no signs that the cancer has spread beyond the breast or the lymph glands in the armpit.

Stage 4 The tumour is of any size, but the lymph nodes are usually affected and the cancer has spread to other parts of the body. This is secondary or metastatic breast cancer. Breast cancer that has come back after initial treatment is known as recurrent breast cancer.

This section deals with stages 1–3 breast cancer. Stage 4 is covered in our secondary breast cancer section.

TNM staging system

Another staging system known as the TNM system is commonly used. This can give more precise information about the extent of the cancer.

• T describes the size of the tumour (cancer)
• N describes whether the cancer has spread to the lymph nodes (sometimes called glands)
• M describes whether the cancer has spread to another part of the body, such as the bone, liver or the lungs. This is known as metastatic or secondary cancer.

Grading refers to the appearance of the cancer cells under the microscope. The grade gives an idea of how quickly the cancer may develop. There are three grades: grade 1 (low-grade), grade 2 (moderate or intermediate grade) and grade 3 (high-grade).

Low-grade means that the cancer cells look very like the normal cells of the breast. They are usually slow growing and are less likely to spread.

In high-grade tumours the cells look very abnormal. They are likely to grow more quickly and are more likely to spread.

Moderate-grade or grade 2 cancers fall between these two grades and have a level of activity somewhere in between.

Some breast cancer cells have receptors, which allow particular types of hormones or proteins to attach to the cancer cell. A sample of the breast tissue will usually be tested to see if it has these receptors. Whether particular receptors are present or not will affect the type of treatment that you will need.

Hormone receptors

Some cancers have receptors for the hormones oestrogen and progesterone. If a breast cancer has a significant number of oestrogen receptors it is known as being oestrogen-receptor positive (ER+). If it doesn’t it is known as oestrogen-receptor negative (ER-). Knowing whether the tumour has oestrogen receptors or not helps the doctors to decide on the best treatment. A tumour that is ER+ is likely to respond to hormonal treatments, whereas a tumour that is ER- will not respond. Oestrogen-receptors are known as ER because of the American spelling of oestrogen as estrogen.

Protein receptors

Some cancers have receptors for a protein known as HER2. Tumours that have high levels of these receptors are known as HER2 positive and may respond to treatment with drugs such as trastuzumab (Herceptin®). Your doctor can tell you whether your cancer cells have these receptors.