As with any medicine, the MHRA will keep the safety and effectiveness of imlunestrant tosylate under close review.
The Medicines and Healthcare products Regulatory Agency (MHRA) has today, 24 February 2026, approved imlunestrant tosylate (Inluriyo), a new treatment for adult patients with a certain type of breast cancer that is locally advanced or has spread to other parts of the body (metastatic) and hasn't responded, or has progressed further, following at least one line of hormonal treatment.
It is used when the cancer cells have oestrogen receptors (ER-positive) and do not have many receptors called human epidermal growth factor receptor 2 (HER2-negative). Inluriyo can only be used in patients who have certain changes (mutations) in a gene called ESR1.
Oestrogen receptors are proteins in cells that activate when the hormone oestrogen binds to them. By binding to these receptors, oestrogen can, in some cases, cause cancer cells to grow and multiply. Imlunestrant binds to oestrogen receptors in the cancer cells, which breaks them down and stops them from working. By blocking and destroying oestrogen receptors, imlunestrant can slow down the growth and spread of breast cancer and help to kill cancer cells.
Imlunestrant tosylate is taken as a daily tablet.
Julian Beach, Interim Executive Director of Healthcare Quality and Access at the MHRA, said:
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 most common side effects with Inluriyo are increased levels of liver enzymes, tiredness, joint, bone and muscle pain, diarrhoea, increased levels of triglycerides (a type of fat in the blood), nausea and back pain.
A full list of side effects can be found in the Patient Information Leaflet (PIL) or the Summary of Product Characteristics (SmPC), which will be published on the MHRA website within 7 days of approval.
As with any medicine, the MHRA will keep the safety and effectiveness of imlunestrant tosylate under close review. Anyone who suspects they are experiencing a side effect from this medicine is encouraged to talk to their doctor, pharmacist or nurse and report it directly to the MHRA Yellow Card scheme, either through the website ( https://yellowcard.mhra.gov.uk ) or by searching the Google Play or Apple App stores for MHRA Yellow Card.
