The National Breast Cancer Audit (NBCA) collects data on:
- early and locally advanced invasive breast cancer (cancer cells invade nearby breast tissue or areas close to the breast such as the armpit, skin, muscles or ribs but have not spread to other parts of the body)
- ductal carcinoma in situ (cancer cells are limited to the breast ducts and do not invade nearby tissue).
This study focused on invasive cancer, which accounted for 88% of New Zealand breast cancer cases collected by the NBCA in 2008.
The study found that in New Zealand:
- Patients were unlikely to have an open biopsy (only 2-3%) which indicates that the large majority of New Zealand patients are diagnosed prior to surgery.
- The 19% re-operation rate was considered acceptable, based on results from other studies.
- A total of 84% of patients did not have a breast reconstruction after mastectomy.
- Overall, 71% of patients with tumours larger than 3cm were treated in line with the New Zealand Guidelines for Early Management of Breast Cancer by receiving a level 2 or 3 axillary clearance (removing lymph nodes in the armpit to test for cancer cells).
- Most (95%) breast conserving surgery patients were treated in line with national guidelines by receiving radiotherapy.
- A total of 84% of high-risk patients (those who have large tumours or more than three lymph nodes containing cancer cells) received radiotherapy after mastectomy. This is just under the 85% required by the NBCA Key Performance Indicator, which was introduced in 2011.
- Overall, 81% of patients with oestrogen-receptor-positive tumours (tumours that need the hormone oestrogen to grow) received hormonal treatment (therapies that block oestrogen).
Patients with early invasive breast cancer in New Zealand generally received treatment in line with national clinical guidelines. The number of high-risk patients not receiving post-mastectomy radiotherapy and the lack of hormonal treatment in some patients with oestrogen-receptor-positive tumours may need further investigation.
BreastScreen Aotearoa
BreastScreen Aotearoa (BSA) is a national breast screening program that offers free screening mammograms to all New Zealand women aged 45 to 69 years with no symptoms of breast cancer. According to NBCA data, over one-third (37%) of New Zealand patients diagnosed with breast cancer in 2008 were referred to a breast surgeon from BSA.
The study found that BSA-referred patients were more likely than non-BSA patients to:
- have smaller tumours
- have less aggressive (grade one) tumours
- have cancer which has not spread to the blood vessels or lymphatic channels
- have cancers that are less common, such as lobular (tumours which originated in the milk-producing lobules of the breast) or tubular (tube-shaped tumours)
- have tumours that are oestrogen-receptor-positive or progesterone-receptor-positive (able to be treated with hormonal therapy)
BSA-referred patients were also:
- more likely to have breast conserving surgery, rather than mastectomy, as a first surgical treatment
- more likely to have sentinel node biopsy (removal and testing of the first lymph node or nodes to which cancer cells are likely to spread) as an alternative to a level 2 or 3 axillary surgery which is a more intrusive procedure
- less likely to be treated with radiotherapy after a mastectomy
- less likely to be prescribed chemotherapy if aged under 70 (chemotherapy was uncommon in patients over 70 in either group).
The differences found in treatment between the BSA and non-BSA referred patients may be due to the high number of small, early-stage cancers in the group of patients screened by BSA. Screening tends to detect slower-growing tumours.