What is breast cancer?

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Breast cancer is one of the most common cancers in the world. More than 44,000 cases are diagnosed in the UK each year, with more than 80% in women over the age of 50 but younger women are sometimes affected. Breast cancer can also develop in men, although this is rare. Breast cancer develops from a cancerous cell which develops in the lining of a duct or lobule in one of the breasts.

There are some 'sub-types' of breast cancer which are important to know as the treatment and prognosis (outlook) vary depending on the exact type of the cancer. The following gives a rough idea of the main sub-types. Your specialist will be able to give you more details as to the exact sub-type of breast cancer that you have.

Invasive or 'in situ'

Most breast cancers are diagnosed when a tumour has grown from within a duct or lobule into the surrounding breast tissue. These are called 'invasive' breast cancers. Invasive breast cancers are also divided into those where cancer cells have invaded into local blood or lymphatic vessels and those that have not.

Some people are diagnosed when the cancerous cells are still totally within a duct or lobule. These are called 'carcinoma in situ' as no cancer cells have grown out from their original site. A carcinoma in situ is easier to treat and has a better outlook than an invasive cancer.

Grade of the cancerous cells

A sample of breast cancer tissue can be looked at under the microscope. By looking at certain features of the cells the cancer can be 'graded'. As a rough guide, the lower the grade, the better the cancer is likely to respond to treatments such as chemotherapy and radiotherapy.

Grade 1 - the cancer cells tend to be slow growing and less 'aggressive'.
Grade 2 - is a middle grade.
Grade 3 - the cancer cells tend to be fast growing and more 'aggressive'.

Hormone responsive or non-hormone responsive

Tests on a sample of breast cancer cells can show if they 'respond' to oestrogen, the main female hormone. Breast cancers are divided into two types:

Oestrogen responsive breast cancer. The cells are stimulated by oestrogen which encourages the cells to divide and multiply. (Treatment can block the oestrogen - see below.)
Non-oestrogen responsive.

Stage of the cancer

This does not describe a type of cancer, but describes how much the cancer has grown and whether it has spread (see below). As a general rule, the earlier the stage, the greater the chance of a cure.

- Next: What causes breast cancer?