This content is part of a paid partnership with Breast Cancer Research Centre-WA.

Dr Louisa Lo
BCRC-WA breast medical oncologist and Education Lead
Louisa completed her breast cancer fellowship training at Peter MacCallum Cancer Centre (Petermac) in Melbourne and is completing her PhD in breast cancer liquid biopsy. She is a principal investigator for breast cancer research studies and has publications in international cancer journals. Dr Lo would like to thank Dr Hilary Martin and Dr Peter Lau for their contributions to this article.

Breast cancer prevention

Prevention of breast cancer is medically possible. In Australia, one in eight women will be diagnosed with breast cancer. In women with moderately (1.5 to 3 times average) and highly (3 times average or greater) increased lifetime risk of breast cancer, personalised risk reducing strategies are available. For example, five years of tamoxifen has been shown, in international studies involving thousands of women, to reduce the relative risk of breast cancer by at least 40% for those who have moderate to high lifetime risk of breast cancer. 

This benefit continues for 20 years after completion of Tamoxifen. In some, this benefit is enough to reduce their lifetime breast cancer risk from moderate to average risk. Tamoxifen is currently available on the PBS, but the uptake is low. 

As well as improving the awareness of drug efficacy and availability in Australia, a woman’s breast cancer risk needs to be accurately estimated. This is usually achieved through genetic counselling. We are especially lucky at BCRC-WA to work alongside Bhavya Vora, an associate genetic counsellor. 

Hormone positive breast cancer

Approximately 70% of breast cancers are hormone positive. Traditionally, women with these breast cancers are recommended adjuvant endocrine treatment +/- chemotherapy to reduce risk of future recurrence and improve probabilities of cancer survival. In premenopausal young women who require adjuvant chemotherapy, adding gonadotrophin releasing hormone (GnRH) agonist, such as goserelin to adjuvant tamoxifen or the aromatase inhibitor Exemestane for five years had been shown to improve both recurrence free and overall survival and is now recommended standard practice in high-risk cases. 

• Adding Abemaciclib

In women who have high risk early breast cancer, the monarchE study had shown that adding two years of abemaciclib, an oral drug that targets the CDK4/6 protein involved in cell cycling, to adjuvant endocrine treatment has led to a 30.4% reduction in the risk of developing new invasive breast cancer or cancer recurrence. The main side effects of this drug are diarrhoea and clinically insignificant neutropenia. This drug is not currently available on PBS. 

• Chemotherapy decisions

To assist with decision making regarding adjuvant chemotherapy, the breast cancer tissue genomic testing Oncotype DX is available. This test is only useful for cancers up to 5cm with no nodal involvement or, if postmenopausal, with low nodal involvement (1-3 nodes). Unfortunately, Oncotype DX is not currently MBS funded and has an out-of-pocket cost of $5000, with a turn-around testing time of about three weeks. 

Her2 positive breast cancer

About 15-20% of breast cancers are the Her2 amplified subtype. Adjuvant trastuzumab has been the poster child of targeted therapy in cancer treatments. Recently, antibody drug conjugates such as trastuzumab emtansine, which has been used to treat metastatic breast cancer, is now being used to treat early breast cancer. Women who needed neoadjuvant treatment for Her2 positive breast cancer will be offered adjuvant trastuzumab emtansine if there is residual invasive disease in the surgical specimen. This has been shown to improve survival rates when compared to using adjuvant trastuzumab alone and is available on PBS. 

• Future treatments

Antibody drug conjugate trastuzumab-Deruxtecan and small molecule Her2 tyrosine kinase inhibitor Tucatinib is carrying great promise in studies, even in previously heavily pretreated patients with Her2 positive breast cancer and with central nervous system involvement. These drugs are currently unavailable. 

Triple negative breast cancer

Chemotherapy treatment is the mainstay here. It is an area of need as it has a relatively poor prognosis. Since the CREATE-X study, six months of adjuvant capecitabine, an oral chemotherapy drug is now prescribed as standard practice if there is residual breast cancer after completion of neoadjuvant treatment. 

• Immunotherapy

Adding immunotherapy pembrolizumab to chemotherapy in the neoadjuvant setting had been shown to improve pathological complete response rates from 56% to 63%. In the metastatic setting, adding pembrolizumab to chemotherapy as first line treatment can improve progression free- and overall survival in patients with high PD-L1 expression (CPS>10). These drugs are not currently available on PBS. 

• Metastatic cancer

Sacituzumab govitecan, an antibody drug conjugate targeting the trophoblast-cell-surface Ag2 (Trop-2) protein has outperformed standard treatment in the landmark ASCENT study even in heavily pretreated patients, regardless of Trop-2 expression. Significant overall survival benefit had been demonstrated and approval has been announced in the Federal Budget for 2022. 

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