Overview

Alpelisib targets the PI3Kα subunit mutated in roughly 40% of HR-positive, HER2-negative breast cancers, and because the PI3K pathway commonly reactivates under endocrine therapy, it is approved specifically in combination with the SERD fulvestrant rather than as monotherapy. The 150 mg tablet in a 28-tablet pack is therefore procured as a companion to an injectable endocrine agent. The combination logic is to strike the escape pathway that lets resistant clones survive anti-estrogen treatment. Understanding the partner drug is essential before ordering.

How It Works

Alpelisib is a selective inhibitor of the p110α catalytic subunit of PI3Kα, the isoform most often mutated by PIK3CA. Blocking it reduces downstream AKT and mTOR signaling that drives proliferation and survival. Critically, PI3K activation is a major mechanism by which HR-positive tumors evade estrogen-deprivation therapy; adding alpelisib collapses that resistance loop. The result is restored sensitivity to fulvestrant, so the two agents act on complementary nodes—one removing estrogen signaling, the other shutting the compensatory survival cascade.

Indications

Alpelisib is indicated for HR-positive, HER2-negative, PIK3CA-mutated advanced or metastatic breast cancer in combination with fulvestrant, after prior endocrine therapy. Eligibility requires a confirmed PIK3CA mutation from tissue or plasma. The combination is preferred over sequential single agents because of the defined resistance interaction. Therapy continues while benefit and tolerability, including glucose control, are maintained.

Dosage & Administration

The oral dose is 300 mg once daily, taken as two 150 mg tablets with food, alongside fulvestrant injections on the labeled schedule. Tablets are swallowed whole. Dose holds or reductions follow rules for hyperglycemia and rash. The 28-tablet pack aligns with a monthly cycle, so supply should be synchronized with the fulvestrant administration visits to avoid gaps in the combined regimen.

Storage & Sourcing

Keep 150 mg tablets at 2–8 °C in the original blister, protected from light and moisture; do not freeze. Ship under a logged refrigerated chain and verify batch, expiry, and seals on receipt. Rotate by earliest expiry. Stock alpelisib and fulvestrant together where possible so the combination course is dispensed as a coordinated pair.

FAQ

Q: Why is alpelisib combined with fulvestrant instead of used alone?

A: PI3Kα mutation drives resistance to estrogen deprivation; fulvestrant removes estrogen signaling while alpelisib shuts the compensatory PI3K survival loop, so together they cover both escape routes.

Q: Which patients carry the PIK3CA mutation that predicts response?

A: Patients with HR-positive, HER2-negative advanced breast cancer who test positive for a PIK3CA mutation in tumor or plasma are the labeled population for the combination.

Q: How does alpelisib restore sensitivity to endocrine therapy?

A: By blocking p110α it stops AKT/mTOR signaling that reactivates under estrogen deprivation, reversing the resistance mechanism and re-sensitizing cells to fulvestrant.

Q: What metabolic monitoring does the combination require?

A: Blood glucose and HbA1c are watched because alpelisib can raise hyperglycemia, with dose holds and anti-diabetic management per the prescribing guidance.