Guideline for Next‑Generation Sequencing in Hormone Receptor‑Positive Metastatic Breast Cancer
1. Indications & Optimal Timing
- NGS should be performed as standard of care after a patient with HR‑positive, HER2‑negative metastatic breast cancer develops resistance to endocrine therapy – this enables detection of actionable genomic alterations that can guide subsequent treatment. 1
- Testing after endocrine‑therapy resistance maximizes the likelihood of identifying ESR1 mutations, which are rare in treatment‑naïve metastatic disease but emerge during aromatase‑inhibitor exposure. 1
2. Specimen Selection
2.1 First‑Line Approach – Circulating Tumor DNA (ctDNA)
- Begin with plasma ctDNA testing when a recent metastatic tissue sample is unavailable; this non‑invasive method provides rapid genomic information. 3
- Plasma testing offers convenience and avoids invasive biopsy procedures. 4
- Plasma ctDNA misses approximately 44 % of PIK3CA mutations that are detectable in tissue specimens, underscoring the need for tissue confirmation when ctDNA is negative. 4
2.2 Reflex to Tissue Testing
- If plasma ctDNA is negative, reflex to tumor tissue NGS is mandatory to avoid false‑negative results. 3
- Use the most recent tumor sample, preferably from a metastatic site, because mutations can be acquired during treatment and receptor status may differ between primary and metastatic disease. 6
3. Practical Testing Algorithm
| Step | Action | Evidence |
|---|---|---|
| 1 | If a recent metastatic biopsy is available, send FFPE tissue for NGS. | [4] |
| 2 | If no recent tissue is available, start with plasma ctDNA testing. | [3] |
| 3 | If plasma ctDNA is negative, obtain a tissue biopsy (if clinically feasible) and send for NGS. | [4] |
| 4 | Avoid bone biopsies when possible, as processing may affect receptor results. | [6] |
4. Actionable Genomic Alterations
4.1 Level IA (Highest Priority)
- ESR1 mutations – prevalence ≈ 9 %; associated with benefit from elacestrant (hazard ratio for progression‑free survival = 0.55). Evidence level: Level IA (based on EMERALD trial). 1
- PIK3CA mutations – prevalence ≈ 39 %; indicate use of alpelisib + fulvestrant after CDK4/6‑inhibitor failure. Evidence level: Level IA. 3
- Somatic BRCA1/2 mutations – prevalence 4–6 %; qualify patients for PARP‑inhibitor therapy (olaparib or talazoparib). Evidence level: Level IA. 1
4.2 Level IIB
- AKT1 or PTEN alterations – FDA‑approved indication for capivasertib + fulvestrant (benefit largely driven by co‑existing PIK3CA mutations). Evidence level: Level IIB. 1
- Somatic BRCA1/2 mutations – PARP inhibitors achieve an objective response rate of ~50 %. Evidence level: Level IIB. 1
- Germline PALB2 variants – PARP inhibitors achieve an objective response rate of ~82 %. Evidence level: Level IIB. 1
5. Germline Testing Considerations
- Tumor NGS misses about 7 % of germline BRCA1/2 mutations; therefore, patients with a high pre‑test probability should undergo dedicated germline testing even if tumor NGS is negative. 1
- High‑risk features prompting germline testing include young age at diagnosis, triple‑negative phenotype, family history of breast/ovarian cancer, and Ashkenazi Jewish ancestry. 3
6. ESR1 Mutation Testing Guidelines
- ESR1 mutations are uncommon in treatment‑naïve metastatic disease and in patients without prior aromatase‑inhibitor exposure. 4
- Testing before endocrine‑therapy resistance yields a low detection rate and may not be cost‑effective. 1
- ASCO guidelines state that evidence is insufficient to recommend routine ESR1 testing, whereas the 2024 ESMO guidelines classify ESR1 as a Level IA alteration based on the EMERALD trial. Evidence level: Level IA (ESMO). 2