The Medicines and Healthcare products Regulatory Agency has approved imlunestrant tosylate (Inluriyo), a new targeted treatment for adults with a specific form of breast cancer that is locally advanced or metastatic and has progressed after at least one line of hormonal therapy.
The approval gives clinicians a new option for treating ER‑positive, HER2‑negative breast cancer in patients whose tumours carry ESR1 gene mutations and are no longer responding to standard hormone‑based treatments.
Inluriyo is authorised for use in patients who meet three key criteria:
- ER‑positive (oestrogen receptor‑positive) breast cancer
- HER2‑negative status
- Presence of ESR1 mutations, which make tumours more likely to resist traditional hormonal therapies
This group of patients typically faces limited treatment options once resistance develops, making the approval of imlunestrant an important development.
Oestrogen receptors are proteins on cancer cells that can trigger growth when activated by oestrogen. Imlunestrant is a selective oestrogen receptor degrader (SERD) – it binds to these receptors, disrupts them, and causes them to break down.
By blocking and destroying oestrogen receptors cancer cell growth is slowed, ensuring that the spread of the disease can be reduced and cancer cells may be killed.
Imlunestrant is taken once daily as an oral tablet, offering a more convenient alternative to injectable or infusion‑based therapies.
Common side effects observed include:
- Raised liver enzyme levels
- Joint, bone and muscle pain
- Diarrhoea
- Raised triglycerides
- Nausea
A full list of side effects will be available in the Patient Information Leaflet (PIL) and the Summary of Product Characteristics (SmPC) on the MHRA website within seven days of approval.
As with all licensed medicines, the MHRA will closely monitor the safety and effectiveness of imlunestrant throughout its use in the UK.
Metastatic ER‑positive, HER2‑negative breast cancer is often treated with hormone‑based therapies, but resistance can develop – particularly when ESR1 mutations are present. The approval of imlunestrant provides a new targeted option designed specifically for this challenging stage of the disease.
Julian Beach, Interim Executive Director of Healthcare Quality and Access at the MHRA, commented:
“Patient safety is our top priority.
“The approval of imlunestrant tosylate (Inluriyo) provides a new treatment for adults with recurrent or metastatic breast cancer after prior hormone treatment hasn’t been effective.
“As with all licensed medicines, we will continue to monitor its safety closely as it becomes more widely used.”
The MHRA’s decision marks an important step in expanding treatment choices and personalising care for patients whose cancer has progressed despite previous hormonal therapies.
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