US Breast Cancer HR+/HER2- Market Sizing Model

A market-sizing model is not a patient-flow model with a price column bolted on; it has to reconcile two things a flow model does not need to. First, HR+/HER2- metastatic breast cancer is a chronic, multi-year condition treated on CDK4/6 inhibitor combination therapy as NCCN's first-line standard of care, so the population generating market value in any given year is not the roughly 19,000 US patients newly presenting with de novo Stage IV disease (6.0% of 316,950 annual invasive diagnoses, SEER), nor even the 73.9%-HR+/HER2- share of that de novo cohort. It is that annual incident flow plus the larger, separately-tracked pool converting to metastatic disease through recurrence after early-stage treatment, still on therapy in year two, three, and beyond. A sizing model built only on annual de novo incidence understates the treated, revenue-generating population by exactly the size of that carried-forward, multi-year base.

Second, the price a sizing model should apply is not a single list number. Palbociclib, the CDK4/6 inhibitor class founder, was selected for Medicare's second IRA negotiation cycle (IPAY 2027): its negotiated 30-day price is $7,871 against a $15,741 list, a 50% cut effective 2027. Ribociclib and abemaciclib are not yet selected and continue to anchor near list. A sizing model that applies list price to the entire population overstates value for the Medicare-covered share; one that applies the negotiated price across the board understates value for the commercial and non-negotiated share. The addressable market value is therefore a range bounded by these two price anchors, weighted by payer mix, not a single point estimate, and the same logic applies downstream: elacestrant's roughly $259,880 annual list price anchors the post-CDK4/6, ESR1-mutant segment until its own negotiation status, if any, is set.

Every AXLRx market sizing model triangulates at least two independent methods before accepting a market-value estimate. This model pairs an epidemiology-based, bottom-up patient-flow build with a price-anchor check across list and Medicare-negotiated pricing, distinct from a Patient Flow Model (static patient count) or a forecasting model (dynamic revenue/uptake curve): a sizing model converts a defensible patient count into a defensible market-value range.

US HR+/HER2- mBC sizing sources: American Cancer Society Breast Cancer Facts & Figures 2024-2025, SEER stage-at-diagnosis trend data, published metastatic subtype incidence-proportion analysis, NCCN Clinical Practice Guidelines in Oncology, the CMS Medicare Drug Price Negotiation Program IPAY 2027 selected-drug list, and the ICER 2025 Launch Price and Access Report.