Nicola Roberts looks subdued as she steps out for a walk with her pet dog... amid former Girls Aloud bandmate Sarah Harding's breast cancer battle

Breast cancer is one of the most common cancers in the world and affects more than two MILLION women a year

Breast cancer is one of the most common cancers in the world. Each year in the UK there are more than 55,000 new cases, and the disease claims the lives of 11,500 women. In the US, it strikes 266,000 each year and kills 40,000. But what causes it and how can it be treated?

What is breast cancer?

It comes from a cancerous cell which develops in the lining of a duct or lobule in one of the breasts.

When the breast cancer has spread into surrounding tissue it is called 'invasive'. Some people are diagnosed with 'carcinoma in situ', where no cancer cells have grown beyond the duct or lobule.

Most cases develop in those over the age of 50 but younger women are sometimes affected. Breast cancer can develop in men, though this is rare.

Staging indicates how big the cancer is and whether it has spread. Stage 1 is the earliest stage and stage 4 means the cancer has spread to another part of the body.

The cancerous cells are graded from low, which means a slow growth, to high, which is fast-growing. High-grade cancers are more likely to come back after they have first been treated.

What causes breast cancer?

A cancerous tumour starts from one abnormal cell. The exact reason why a cell becomes cancerous is unclear. It is thought that something damages or alters certain genes in the cell. This makes the cell abnormal and multiply 'out of control'.

Although breast cancer can develop for no apparent reason, there are some risk factors that can increase the chance, such as genetics.

What are the symptoms of breast cancer?

The usual first symptom is a painless lump in the breast, although most are not cancerous and are fluid filled cysts, which are benign. 

The first place that breast cancer usually spreads to is the lymph nodes in the armpit. If this occurs you will develop a swelling or lump in an armpit.

How is breast cancer diagnosed?

• Initial assessment: A doctor examines the breasts and armpits. They may do tests such as a mammography, a special x-ray of the breast tissue which can indicate the possibility of tumours.
• Biopsy: A biopsy is when a small sample of tissue is removed from a part of the body. The sample is then examined under a microscope to look for abnormal cells. The sample can confirm or rule out cancer.

If you are confirmed to have breast cancer, further tests may be needed to assess if it has spread. For example, blood tests, an ultrasound scan of the liver or a chest X-ray.

How is breast cancer treated?

Treatment options which may be considered include surgery, chemotherapy, radiotherapy and hormone treatment. Often a combination of two or more of these treatments are used.

• Surgery: Breast-conserving surgery or the removal of the affected breast depending on the size of the tumour.
• Radiotherapy: A treatment which uses high energy beams of radiation focused on cancerous tissue. This kills cancer cells, or stops them from multiplying. It is mainly used in addition to surgery.
• Chemotherapy: A treatment of cancer by using anti-cancer drugs which kill cancer cells, or stop them from multiplying.
• Hormone treatments: Some types of breast cancer are affected by the 'female' hormone oestrogen, which can stimulate the cancer cells to divide and multiply. Treatments which reduce the level of these hormones, or prevent them from working, are commonly used in people with breast cancer.

How successful is treatment?

The outlook is best in those who are diagnosed when the cancer is still small, and has not spread. Surgical removal of a tumour in an early stage may then give a good chance of cure.

The routine mammography offered to women between the ages of 50 and 70 means more breast cancers are being diagnosed and treated at an early stage.

For more information visit breastcancernow.org or call its free helpline on 0808 800 6000