The Medicines and Healthcare products Regulatory Agency (MHRA) has approved imlunestrant tosylate, marketed as Inluriyo, as a new treatment option for certain adults with advanced breast cancer.
Announced on 24 February 2026, the approval covers adult patients with oestrogen receptor-positive (ER-positive), human epidermal growth factor receptor 2-negative (HER2-negative) breast cancer that is either locally advanced or metastatic and has progressed following at least one line of hormonal therapy. The treatment is specifically indicated for patients whose tumours carry particular mutations in the ESR1 gene.
ER-positive breast cancers depend on oestrogen signalling for growth. Oestrogen receptors are proteins within cells that activate when bound by the hormone oestrogen, which can drive tumour cell proliferation in some cancers. Imlunestrant works by binding directly to these oestrogen receptors, breaking them down and preventing them from functioning. By blocking and degrading the receptors, the medicine aims to slow tumour growth, limit disease spread and promote cancer cell death.
Imlunestrant tosylate is administered as a once-daily oral tablet, offering a convenient treatment option for eligible patients whose disease has become resistant to prior hormone-based therapies.
The most commonly reported side effects include elevated liver enzymes, fatigue, joint, bone and muscle pain, diarrhoea, increased triglyceride levels, nausea and back pain. A comprehensive list of adverse effects will be available in the Patient Information Leaflet (PIL) and the Summary of Product Characteristics (SmPC), which are scheduled to be published on the MHRA website within seven days of approval.
The MHRA stated that, as with all authorised medicines, the safety and effectiveness of imlunestrant tosylate will continue to be monitored closely as its use expands in clinical practice. Patients and healthcare professionals are encouraged to report any suspected side effects through the MHRA Yellow Card scheme, either via its website or the mobile application available on major app platforms.
The approval adds a targeted therapeutic option for patients with ESR1-mutated, hormone-resistant metastatic breast cancer, a subgroup with limited treatment choices once initial endocrine therapies lose effectiveness.
