HR+/HER2- breast cancer is 68% of US cases, but the 20-30% who recur to metastatic disease define the market.

Breast cancer is the most common non-skin cancer in US women, with the American Cancer Society estimating roughly 317,000 new invasive female cases in 2025. Hormone receptor-positive, HER2-negative disease, meaning ER and/or PR positive with HER2 not overexpressed, is the dominant molecular subtype at approximately 68% of cases per SEER data. The overwhelming majority present as early-stage, endocrine-sensitive disease treated with surgery, radiation, and adjuvant endocrine therapy, and is largely curable. Only about 6% present as de novo stage IV. The metastatic population driving the systemic-therapy market comes mainly from the estimated 20-30% of early-stage patients who later recur.

In the metastatic setting the clinical pathway is defined by biomarker testing layered on top of standard ER/PR/HER2 immunohistochemistry. First line is endocrine therapy, an aromatase inhibitor or fulvestrant, plus a CDK4/6 inhibitor. At progression, molecular testing on tissue or circulating tumor DNA directs the next line: ESR1 mutations, detected in roughly 48% of CDK4/6-pretreated patients in EMERALD, open the door to the oral SERD elacestrant; PIK3CA mutations, in about 40% of HR+/HER2- disease per SOLAR-1, direct patients to alpelisib; AKT-pathway alterations direct patients to capivasertib. Serial genomic testing, not a single line of therapy, structures this pathway.

Recurrence, not incidence, is what defines the treatable market.

Five questions this report answers:

Q1 - How large is the addressable HR+/HER2- metastatic population in the US?

Q2 - Which biomarkers, ESR1 and PIK3CA, must be tested and when along the pathway?

Q3 - How does treatment intent change from early to metastatic disease?

Q4 - What is the US epidemiology and clinical treatment pathway of HR+/HER2- breast cancer?

Q5 - What share of HR+/HER2- patients present as de novo stage IV versus later recurrence?

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Mike || Global Pharma Commercial Marketing Head

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