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Mammograms – a woman’s guide


This article outlines the benefits and risks of mammography and provides information on the New-Zealand scheme.

Mammograms – a woman’s guide


Breast cancer is the most common cancer in New Zealand women and the risk of developing breast cancer increases with age.


Currently in New Zealand there is a free national breast screening programme for women aged 45-69 years which involves having a mammogram every 2 years. If a screening mammography indicates an abnormality, the woman will most likely be recommended for further breast imaging (i.e. with spot view mammography, ultrasound or other imaging tests). If further imaging confirms or reveals an abnormality, the woman may be referred for biopsy to determine whether or not she has breast cancer.


Enrolment into the breast screening programme


Women can choose to enter into this breast screening programme by contacting BreastScreen Aoteoroa phoning 0800 270 200 or enrolling online at:



Who is eligible?


To be eligible for a free screening mammogram every two years through BreastScreen Aotearoa a woman must meet the following requirements:


• be aged 45 to 69 years of age


•have no signs/symptoms of breast cancer (If a woman has had breast cancer in the past, she can enter or re-enter the breast screening programme five years from when her cancer was found).


not have had a mammogram in the last 12 months


not be pregnant


• be eligible for public health services in New Zealand.


Note: women with breast implants can still be screened


Making the decision to be screened


The decision to enter into any screening programme involves a look at the advantages and disadvantages (i.e. the pros and cons).



The advantages of mammography as a screening tool for breast cancer:


v  The aim of breast screening is to find very small cancers before a lump can be felt in the breast(s). Early treatment has the best chance of success: if breast cancer is caught and treated while it is still confined to the breast ducts (DCIS: ductal carcinoma in situ), the cure rate is close to 100%.


v  The U.S. Food and Drug Administration (FDA) reports that mammography can find approx 85% of breast cancers in women over 50 and can discover a lump up to two years before it can be felt.


v  Regular screening with mammography cannot prevent breast cancer, but it can reduce the risk of dying from breast cancer. Research shows that when women aged 50 years and over are invited to have mammograms every two years as part of a screening programme, their risk of death from breast cancer is reduced by about a third. For women aged 45 to 49 years, the risk of death from breast cancer is reduced by about a fifth(ref 1).


v  The procedure is safe: there's only a very tiny amount of radiation exposure from a mammogram. Modern mammography systems use extremely low levels of radiation: usually about 0.1 to 0.2 rad dose per x-ray (rad is the scientific unit of measure of radiation energy dose). To put mammography dose into perspective, a woman who receives radiation therapy as a treatment for breast cancer will receive several thousands rads. If a woman had screening mammography for 25 years (two x-ray views per breast), beginning at age 45 years and continuing until age 69, she will have received of a total of 5 rads to 10 rads per breast in that time. Only doses 100-1000 times greater those used for mammography are required to show any statistical increase in breast cancer frequency


The disadvantages of mammography as a screening tool for breast cancer:


v  Screening can lead to overdiagnosis and overtreatment (estimated at 30% (ref 2)). Overdiagnosis and overtreatment mean that supposed “abnormalities” can in fact be breast lesions that would have been fine to have been left alone.


v  Some women can experience psychological distress (i.e. anxiety) because of false positive findings e.g. if the mammogram shows something that could represent a malignancy (cancer), the woman is recalled for additional investigations. In some cases it turns out that what was seen on the mammogram was benign (i.e. not cancer), and that it was therefore a false alarm.


v  Pain at the examination - The breast is squeezed flat between two plates during a mammogram. It only takes a few moments, but about half of women find it painful. Sometimes it can be helpful to schedule the mammogram to take place just after a menstrual period (in a pre-menopausal woman) or to take analgesia (pain relief) just prior to the mammogram


v  False reassurance – Some cancers (approx 15%) can not be detected by mammography therefore important for woman to see their doctor if she finds a lump in her breast, even if she has had a mammogram recently. Breast cancer may not be visible on a screening mammogram if the cancer is : very small, in an area that is not easily imaged with mammography (e.g. the axilla (underarm region) or it is obscured by other shadows





1.Nyström L, Rutqvist LE, Wall S, Lindgren A, Lindqvist M, Ryden S, et al.

Breast cancer screening with mammography: overview of Swedish

randomised trials. Lancet 1993; 341:973–8.


2. Giles GG, Amos A. Evaluation of the organised mammographic screening

programme in Australia. Annals of Oncology 2003; 14:1209-11.

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