Medical oncologists from New Zealand and Australia met recently in Brisbane to discuss research progress with oral SERDs (selective oestrogen receptor degraders) for treating hormone receptor positive breast cancer. These medicines work by reducing oestrogen levels and keeping cancer cells in check.

For more than 20 years, there has been little change in endocrine therapies for hormone receptor positive (HR+) HER2 negative breast cancer. In the 1980s tamoxifen, which blocks oestrogen in the breast, was shown to dramatically reduce recurrence. In the early 2000s, aromatase inhibitors (AIs: anastrozole, letrozole and exemestane) were added to treatment regimes. These medicines are effective but sometimes result in treatment resistance. Endocrine therapy needs to be taken for many years to be effective and over that time, some breast cancer cells can mutate and become resistant to treatment.  The ESR1 mutation is one example of this.

Between 2021 and 2024, a completely new type of medicine was developed for HR+ breast cancer. CDK 4/6 inhibitors (palbociclib, ribociclib and abemaciclib) interfere with cancer cell division. These medicines are used to treat advanced HR+ breast cancer, and recently abemaciclib and ribociclib combined with endocrine therapy have also been shown to be effective in treating early ‘high-risk’ HR+ breast cancer. 

Oral SERDs are the latest innovation in treating HR+ breast cancer. Fulvestrant is an injectable SERD that many will already be familiar with, but pill versions of similar drugs are under development. There are several candidates currently being tested in trials using different strategies to overcome the resistance problems that arise with ESR1 mutations.

In most of the current trials oral SERDs are combined with other medicines to treat advanced HR+ HER2- breast cancer, but there are also some promising results with oral SERDs being used for early- stage HR+ breast cancer.

Giredestrant

The persevERA trial looked at giredestrant in combination with palbociclib. Results showed some improvements in progression-free survival but these were not statistically significant. The treatment was safe and tolerable. There are other trials under way looking at giredestrant: evERA (with everolimus), pionERA (with CDK 4/6 inhibitors versus fulvestrant), and lidERA (for early breast cancer). Positive results from lidERA have led manufacturer Roche to apply to the US regulator FDA for giresdestrant to be approved for use in early-stage HR+ breast cancer (read more here). 

Camizestrant

In the SERENA series of trials camizestrant was combined with CDK 4/6 inhibitors. Positive results so far in reducing the risk of disease progression have led the manufacturer Astra Zeneca to seek approval for this medicine’s use in the EU (read more here).

Palezestrant

The OPERA-01 trial compares palecestrant as a treatment on its own with standard endocrine therapy in patients with advanced HR+ HER2- breast cancer who have progressed after treatment with a CDK4/6 inhibitor. OPERA-02 is evaluating palazestrant combined with ribociclib in this setting.

Elascestrant

The EMERALD trial showed that elacestrant significantly improves progression-free survival compared to standard endocrine therapy in HR+ HER2- advanced breast cancer, especially for patients with ESR1 mutations after prior CDK4/6 inhibitor treatment. The US regulator FDA has now approved the use of elascestrant (brand name Orserdu).

Imlunestrant

In the EMBER trial imlunestrant plus abemaciclib improved progression-free survival compared with imlunestrant monotherapy. Imlunestrant alone also outperformed standard endocrine therapy in patients with ESR1 mutations. Manufacturer Eli Lilley applied to Australia’s Therapeutic Goods Authority (similar to NZ’s Medsafe) for imlunestrant approval in April 2025, and the US FDA approved this medicine in September 2025.

In conclusion, these new medicines are showing promise, with some approved for use in some countries already, but oncologists are not yet in agreement about the best ways to use them. The picture should become clearer as more trials results come in.

Currently there are no publicly funded oral SERDs in Australia or New Zealand, and ESR1 mutation tests are not routinely available. 

21 August 2026