The Menarini Group and its subsidiary Stemline Therapeutics disclosed new Phase 1b/2 ELEVATE data for elacestrant in combination with capivasertib in patients with estrogen receptor-positive, HER2-negative locally advanced or metastatic breast cancer. The ASCO 2026 update places the oral selective estrogen receptor degrader into a broader combination strategy aimed at patients whose disease may be driven by overlapping endocrine resistance and PI3K pathway alterations.

Why the elacestrant and capivasertib combination matters for ER-positive metastatic breast cancer treatment sequencing

The significance of the ELEVATE update is not that elacestrant is entering breast cancer for the first time. It is already established as an oral endocrine therapy option for patients with estrogen receptor-positive, HER2-negative, ESR1-mutated advanced or metastatic breast cancer after progression on endocrine therapy. The more important question is whether elacestrant can move from a single-agent oral SERD into a flexible endocrine backbone that can be combined with targeted agents across different resistance pathways.

That distinction matters because estrogen receptor-positive, HER2-negative metastatic breast cancer is increasingly treated through biomarker-directed sequencing rather than one-size-fits-all endocrine escalation. After prior endocrine therapy and CDK4/6 inhibitor exposure, many patients develop molecular drivers of resistance that make later-line treatment decisions more complex. ESR1 mutations can reduce the effectiveness of aromatase inhibitor-based approaches, while PIK3CA, AKT1, and PTEN alterations can activate growth pathways that continue to support tumour progression even when estrogen receptor signalling is targeted.

The elacestrant plus capivasertib arm is therefore testing a commercially and clinically important idea: whether a fully oral endocrine and AKT pathway combination can address two resistance layers at the same time. If that concept holds in larger studies, Menarini could position elacestrant not just as an alternative to standard endocrine therapy, but as a platform around which combination regimens are built. The unresolved issue is that ELEVATE remains early, open-label, and small, so the signal is hypothesis-strengthening rather than practice-changing.

What the Phase 1b ELEVATE results reveal about efficacy signals and why the dataset remains early

The reported ELEVATE data include 31 patients treated across elacestrant and capivasertib dose cohorts, with the recommended Phase 2 dose identified as elacestrant 345 mg plus capivasertib 320 mg twice daily on a four-days-on, three-days-off schedule. In response-evaluable patients in the recommended Phase 2 dose cohort, the combination showed an 88.9 percent disease control rate, a 66.7 percent clinical benefit rate at 24 weeks, and a 33.3 percent objective response rate. Preliminary median progression-free survival was 11.3 months in the overall recommended Phase 2 dose population and 10.9 months in patients with co-existing ESR1 and PIK3CA mutations.

Those numbers are clinically interesting because they appear in a treatment context where resistance biology often determines whether endocrine-based therapy can continue to delay chemotherapy. The fact that all patients with objective responses had co-existing ESR1 and PIK3CA mutations gives the dataset a clear biological story. It supports the rationale that simultaneously degrading the estrogen receptor and blocking AKT pathway signalling may be particularly relevant in tumours where both pathways are implicated.

However, the same feature also creates caution. A small response-evaluable cohort can produce impressive percentages that may not remain stable when tested in a broader population. The recommended dose cohort contained only nine patients, meaning each patient outcome carries substantial statistical weight. Median duration of response had not yet been reached, which is encouraging but also immature. For clinicians and regulators, the next question will be whether the efficacy pattern persists in a larger Phase 2 dataset with more robust stratification by ESR1, PIK3CA, AKT1, and PTEN status.

How the oral combination strategy compares with existing endocrine and targeted therapy options

The competitive context is especially important because capivasertib already has an established role in combination with fulvestrant for hormone receptor-positive, HER2-negative advanced or metastatic breast cancer with PIK3CA, AKT1, or PTEN alterations after progression on endocrine-based therapy. That makes the elacestrant combination less about introducing AKT inhibition into breast cancer and more about asking whether the endocrine partner can be upgraded from injectable fulvestrant to an oral SERD with activity in ESR1-mutated disease.

This is where Menarini’s strategy becomes more commercially interesting. Fulvestrant remains a widely used endocrine backbone, but it is administered by intramuscular injection and has limitations in estrogen receptor degradation. Elacestrant offers an oral alternative with a differentiated profile in ESR1-mutated disease, which may be attractive in combination regimens if tolerability, adherence, and efficacy are preserved. For oncologists, an all-oral regimen could simplify treatment logistics, particularly for patients who are already managing chronic metastatic disease with repeated clinic visits and molecular testing.

Still, convenience alone rarely changes prescribing behaviour in oncology. A new oral combination would need to show that it can deliver clinically meaningful disease control without adding intolerable toxicity, drug interaction complexity, or reimbursement friction. It would also need to prove where it belongs relative to capivasertib plus fulvestrant, PI3K inhibitor combinations, mTOR inhibitor combinations, CDK4/6 rechallenge strategies, antibody-drug conjugates, and chemotherapy. In other words, the commercial prize is clear, but the sequencing battle is crowded.

Why co-existing ESR1 and PIK3CA mutations could become the most important subgroup to watch

The most analytically important part of the update is the focus on co-existing ESR1 and PIK3CA mutations. These alterations represent a biologically plausible overlap in which endocrine resistance and growth pathway activation may both be driving disease progression. For a patient population that has often received prior endocrine therapy and CDK4/6 inhibition, that overlap could become a practical biomarker-defined niche for combination endocrine therapy.

If future data confirm the early signal, Menarini could argue that elacestrant plus capivasertib is not merely another endocrine combination, but a precision oncology regimen aimed at dual resistance. That would fit broader treatment trends in metastatic breast cancer, where molecular testing is increasingly used to identify ESR1 mutations, PIK3CA mutations, AKT1 alterations, PTEN loss, HER2-low status, and other actionable or treatment-informing features. The more precisely a regimen maps to a resistance pattern, the easier it becomes to justify clinical adoption and payer interest.

The limitation is that biomarker-defined opportunity can also narrow the addressable population. A combination designed around ESR1 and PIK3CA co-alteration may have a strong rationale, but it must prove whether benefit extends to patients with only one of these alterations or with other PI3K pathway changes. If the strongest activity is concentrated in a small molecular subset, the regimen could still be valuable, but its commercial profile would depend heavily on testing rates, physician awareness, and how quickly patients are identified before they move to non-endocrine options.

What Menarini’s broader elacestrant program says about its breast cancer expansion strategy

The ELEVATE update should be read alongside Menarini’s wider elacestrant development program rather than as an isolated poster-level data point. The Italian pharmaceutical and diagnostics group is evaluating elacestrant across several settings, including combinations with alpelisib, everolimus, capivasertib, palbociclib, ribociclib, and abemaciclib. Additional studies are examining elacestrant in early breast cancer, in ESR1-mutated advanced disease with everolimus, and in combination approaches involving patients with brain metastases.

This breadth suggests that Menarini is trying to build elacestrant into a franchise asset rather than allow it to remain confined to a narrow approved indication. The strategy is logical. In estrogen receptor-positive breast cancer, endocrine therapy remains a central treatment pillar, but resistance develops through multiple mechanisms. A drug that can serve as a tolerable oral backbone across targeted combinations could have far greater strategic value than a monotherapy used only after progression on earlier lines.

The risk is execution complexity. A broad combination program can generate many useful signals, but it also creates competing priorities. Menarini will need to decide which combinations deserve late-stage investment, which biomarker populations justify pivotal development, and where the probability of reimbursement is strongest. The sector has already seen promising endocrine combinations face adoption barriers when toxicity, sequencing uncertainty, or marginal incremental benefit weakens the case for routine use.

Why safety and tolerability will be central to whether this regimen can scale

The early safety description suggests the elacestrant and capivasertib regimen was consistent with the known profiles of the individual targeted therapies and standard endocrine therapy. That is important because tolerability is not a secondary concern in this treatment class. Patients with hormone receptor-positive metastatic breast cancer may remain on therapy for extended periods, and chronic toxicity can directly affect persistence, quality of life, and clinician willingness to use a regimen before chemotherapy.

Capivasertib combinations can involve adverse events such as diarrhoea, rash, hyperglycaemia, and other class-related tolerability issues, while endocrine therapies carry their own side effect considerations. Combining targeted agents may strengthen efficacy, but it can also create cumulative management burdens. An all-oral regimen may reduce clinic logistics, but it also shifts more responsibility to adherence monitoring, dose interruption management, and patient education.

That means the Phase 2 portion of ELEVATE will need to do more than confirm progression-free survival. It will need to clarify dose intensity, discontinuation rates, adverse event management, and whether the four-days-on, three-days-off capivasertib schedule supports durable treatment exposure in real-world-like patients. In metastatic breast cancer, a regimen that is effective but difficult to sustain can lose ground quickly to alternatives with simpler management.

How regulatory and commercial observers may interpret the ELEVATE signal after ASCO 2026

From a regulatory perspective, the current dataset is too early to define a pathway on its own. It supports further development, but it does not yet establish comparative benefit. Regulators would likely need randomized evidence showing that elacestrant plus capivasertib improves clinically meaningful outcomes over an appropriate control, especially in a biomarker-selected population. The key design question is whether a future trial would compare the regimen against capivasertib plus fulvestrant, endocrine therapy alone, another targeted combination, or physician’s choice after prior CDK4/6 inhibitor therapy.

Commercially, the signal gives Menarini a stronger story around elacestrant’s role as a combination partner. That matters because oral SERDs are a competitive field, and differentiation increasingly depends on evidence beyond monotherapy. A therapy that can show combinability with AKT, mTOR, PI3K, and CDK4/6 pathway agents may become more strategically relevant to oncologists and partners than a drug supported only by a single approved use case.

Yet the commercial bar is rising. Breast cancer treatment is moving rapidly, and clinicians are already balancing endocrine-based regimens with antibody-drug conjugates, targeted therapies, and later-line chemotherapy. To win durable attention, Menarini will need to show that elacestrant combinations can delay escalation without compromising future treatment options. The next meaningful milestone is not merely another small-cohort update, but a clearer signal that one or more combinations can survive randomized testing.

What clinicians and industry observers are likely to watch next in elacestrant development

The next phase of scrutiny will focus on whether the recommended Phase 2 dose cohort expands cleanly and whether the co-existing ESR1 and PIK3CA mutation signal remains consistent. Clinicians will want to see whether response rates translate into durable progression-free survival, whether clinical benefit is maintained after prior CDK4/6 inhibitor exposure, and whether patients with different PI3K pathway alterations respond similarly. Industry observers will also watch whether elacestrant’s combination profile looks meaningfully different from fulvestrant-based regimens.

The broader strategic question is whether Menarini can convert elacestrant into a modular endocrine platform. ELEVATE is structured around that ambition. By testing elacestrant with multiple targeted classes, the program gives Menarini several routes toward expansion, but it also forces the group to identify the combinations that offer the clearest clinical and commercial return. In oncology development, breadth is useful only if it eventually produces a sharply defined pivotal path.

For now, the ELEVATE capivasertib arm strengthens the rationale for oral endocrine and targeted combinations in estrogen receptor-positive, HER2-negative metastatic breast cancer. The data are not definitive, but they are directionally important. They show that Menarini’s elacestrant strategy is moving beyond the question of whether an oral SERD can work after endocrine resistance and into the more valuable question of whether it can anchor the next generation of biomarker-directed breast cancer combinations.

  AKT inhibitor, ASCO 2026, capivasertib, Elacestrant, ELEVATE study, endocrine therapy, ER-positive breast cancer, ESR1 mutation, HER2-negative breast cancer, metastatic breast cancer, oral SERD, PIK3CA mutation, Stemline Therapeutics, The Menarini Group