Breast Cancer

Breast cancer is the most common form of cancer among New Zealand women.   One in nine New Zealand women will develop breast cancer at some stage of their lives. 


Initial symptoms will normally include a new lump in the breast; treatment will generally involve surgery followed by a combination of other treatments such as chemotherapy or radiotherapy.  Men can develop breast cancer though it is rare. Around 20 men are diagnosed with the condition in New Zealand each year, which equates to around 1% of all breast cancer diagnoses. 

In New Zealand breast cancer accounted for 27.5% of all cancer registrations in 2010 and was the second leading cause of cancer death in women behind lung cancer; in real numbers, that translates to around 2800 diagnoses and 650 deaths from the disease;

Breast cancer occurs when breast cells develop abnormally and grow out of control forming a malignant (cancerous) tumour. It is possible for cancer cells to spread (metastasise) from the breast to other parts of the body via the lymphatic system and by direct entry into the blood vessels. Once there, they can form "secondary" cancers.

Prior to menopause the majority of new breast lumps found are benign (non-cancerous).  However, after menopause one in two new breast lumps found will be malignant.  Approximately 75% of all breast cancers will occur in women over the age of 50 years.   Internationally, breast cancer rates have increased in most developed countries over the last 40 years.

Breast cancer can recur.  Once a woman has had breast cancer her chances of developing it again are increased fivefold.

The causes of breast cancer are not known. However, it is known which women are more at risk of developing the condition. The main risk factors for developing breast cancer are:

  • Being a woman over the age of 40 years.
  • Having a family history of breast cancer - the younger the family member was when they developed breast cancer, the greater the risk.
  • Having had breast cancer previously.
  • Having had a biopsy showing an "at risk" breast lump or thickening.
  • Having a breast cancer gene (BRCA-1 or BRCA-2). Women with a breast cancer gene have a 50% chance of developing breast cancer before the age of 70.

Other risk factors include:

  • Having had an early onset of periods or the late onset of menopause.
  • Having had a first child after the age of 30 years or not having had children at all.
  • A diet high in fat, excessive alcohol and a reduced intake of fibre, fruits and vegetables.
  • Being on HRT medication for longer than 5-7 years.
  • Taking the oral contraceptive pill may slightly increase the risk of developing breast cancer, but this has not been conclusively proven.
  • Having dense breasts - dense breasts do not increase the risk of developing breast cancer, but they may make lumps difficult to feel and see.
  • Being in a high socio-economic group or having Jewish ancestry may also be risk factors for developing breast cancer.

There are several different types of breast cancer. The two most common types are ductal breast cancer (to do with the milk ducts) and lobular breast cancer (to do with the milk lobules). Each of these breast cancers can be either “in situ” or “invasive”.


In situ carcinoma: These are pre cancers and are the earliest stage of breast cancer; they can either develop into invasive breast cancer or raise the risk of developing invasive cancer. Caught and treated early, they are often completely curable.


Ductal carcinoma in situ (DCIS): This is where the breast cancer cells are completely contained within the milk ducts and have not spread into the surrounding breast tissue.  DCIS is usually treated with surgery (mastectomy) or combined surgery (partial mastectomy) and radiotherapy.


Lobular carcinoma in situ (LCIS): This is where the breast cancer cells are completely contained within the milk lobules and have not spread into the surrounding breast tissue. Often LCIS does not need treatment. Instead, regular breast exams and mammograms may be used to monitor for the early changes of developing breast cancer.


Invasive carcinoma: This is where the ductal or lobular cancer spreads into the surrounding tissues. Approximately 90% of invasive breast cancers are ductal cancers.

Other less common breast cancers include inflammatory breast cancer and medullary breast cancer.