Synthesis: Genomic and transcriptomic profiling in clinical use

Evidence grades (GRADE-adapted): A high — multiple well-conducted RCTs or systematic reviews converge. B moderate — single pivotal RCT or consistent observational evidence. C limited — single observational study, mechanistic, or expert consensus. D preclinical / hypothesis-generating.

Where genomic profiling sits in TNBC care

Genomic profiling has progressed from a research tool to a standard component of metastatic TNBC workup over the past decade. The principal clinical roles:

• Germline BRCA1/2 (and broader panel) testing — recommended for all TNBC patients per NCCN. Gates PARP-inhibitor eligibility (OlympiAD, EMBRACA, OlympiA).
• Tumor genomic profiling — for metastatic TNBC, identifies somatic BRCA1/2 mutations (PARP candidates), PIK3CA mutations (PI3K inhibitor consideration), NTRK fusions (TRK inhibitor candidates), MSI/MMR status (tissue-agnostic pembrolizumab), and TMB (tumor mutational burden, supporting pembrolizumab in TMB-high tumors).
• Clinical-trial eligibility — many phase I/II trials require comprehensive genomic profiling for eligibility screening.
• Liquid-biopsy ctDNA — for non-invasive monitoring, resistance detection, and tumor-only profiling when tissue is limited.

Comprehensive tumor profiling platforms

FoundationOne CDx

Foundation Medicine's FoundationOne CDx is an FDA-approved comprehensive genomic profiling test covering 324 cancer-related genes plus select select rearrangements, microsatellite instability, tumor mutational burden, and HRD-related features. It is FDA-cleared as a companion diagnostic for multiple targeted therapies across cancer types. Sample requirement is approximately 30 ng of DNA from FFPE tumor tissue (typically 10–20 mm² of tissue area).

In TNBC, key FoundationOne findings include BRCA1/2 mutations, PIK3CA mutations, NTRK fusions, MSI status, TMB, and HRD signature. Turnaround time is typically 7–14 days; report is delivered electronically.

Tempus xT and xR

Tempus's xT is a 648-gene DNA panel; xR is an RNA-seq companion that adds fusion detection and expression profiling. The combination provides comprehensive DNA/RNA profiling with integrated reporting. Tempus also reports germline findings from the same sample if normal control is provided.

Caris MI Profile

Caris Life Sciences offers a multi-omic profiling test that combines DNA sequencing, RNA sequencing, IHC for selected markers, and protein expression analysis. The integrated report includes biomarker-driven treatment recommendations and clinical trial matching.

MSK-IMPACT

MSK-IMPACT is an academic-medical-center-developed tumor profiling test from Memorial Sloan Kettering covering 505 cancer-related genes. Used primarily at MSK and partner institutions; not commercially available in the same way as Foundation, Tempus, or Caris. Provides similar information density.

Targeted single-gene and small-panel tests

Germline BRCA1/2 testing

The most consequential test for TNBC because it gates PARP inhibitor eligibility (metastatic per OlympiAD/EMBRACA; adjuvant per OlympiA). Available through Myriad Genetics (the original BRCA testing provider), Invitae, Ambry, Color, and many academic medical centers. Multi-gene panels increasingly include PALB2, ATM, CHEK2, and other HR-related genes in addition to BRCA1/2.

The Daly 2021 NCCN guideline insights^[1]A recommends germline testing for all TNBC patients regardless of age, family history, or ancestry. Genetic counselor involvement is recommended before and after testing.

PIK3CA testing

PIK3CA mutations are found in approximately 10–15% of unselected TNBC and approximately 50% of the LAR subtype. Testing options include FoundationOne (as part of comprehensive profiling), focused mutation panels (Therascreen, others), and ctDNA-based testing (Guardant360, Tempus xF).

In HR+ metastatic breast cancer, PIK3CA mutations gate alpelisib eligibility (SOLAR-1 trial). In TNBC, PIK3CA mutations don't currently have an FDA-approved targeted therapy indication, but are relevant for clinical-trial eligibility (LAR-targeted combinations) and may inform future treatment options.

NTRK fusion testing

NTRK1/2/3 fusions are rare in TNBC overall (estimated < 1%) but are clinically important when present because they gate tissue-agnostic TRK inhibitor approval (larotrectinib, entrectinib). Detection requires RNA-seq or NTRK-specific FISH; comprehensive tumor profiling panels typically include NTRK fusion detection.

Secretory carcinoma of the breast (a rare histologic subtype that may present as TNBC) is characterized by ETV6-NTRK3 fusions and is highly responsive to TRK inhibitors.

MSI / MMR testing

Microsatellite instability (MSI-high) or mismatch-repair deficiency (dMMR) is rare in breast cancer overall (~2%) but is clinically important because it gates tissue-agnostic pembrolizumab approval. MSI is detectable by IHC for MLH1/MSH2/MSH6/PMS2 protein expression, PCR-based microsatellite analysis, or NGS-based assessment.

Tumor mutational burden (TMB)

TMB ≥ 10 mutations/Mb gates tissue-agnostic pembrolizumab approval based on the KEYNOTE-158 results. Approximately 5–10% of TNBC tumors meet this threshold, providing an additional pembrolizumab option for select patients beyond the standard CPS ≥ 10 indication.

Liquid-biopsy ctDNA platforms

ctDNA from peripheral blood provides a non-invasive alternative to tissue biopsy, with several clinical-grade platforms available:

• Guardant360 — FDA-approved 74-gene panel for solid tumors. Particularly used when tissue is insufficient or when serial monitoring is desired.
• Foundation Medicine Liquid CDx — FDA-approved 324-gene liquid panel with selected companion-diagnostic indications.
• Tempus xF — 105-gene liquid panel.
• Signatera — tumor-informed personalized ctDNA assay for minimal residual disease (MRD) monitoring after curative-intent treatment.
• RaDaR (Inivata) — similar personalized MRD platform.

ctDNA applications:

• Initial profiling at metastatic diagnosis when tissue is limited
• Resistance detection at progression on targeted therapy (BRCA reversion mutations during PARP inhibitor therapy, for example)
• MRD monitoring after curative-intent treatment; emerging evidence suggests ctDNA-positive status after KEYNOTE-522 may identify higher-risk patients who could benefit from treatment intensification
• Tumor heterogeneity assessment — ctDNA reflects multiple metastatic sites simultaneously, potentially capturing heterogeneity that single-site tissue biopsy misses

ctDNA limitations: tumors that shed low ctDNA produce false-negative results; small variants may be missed at low allele frequencies; CNS metastases shed less to peripheral blood (CSF ctDNA more sensitive for CNS-only disease).

Transcriptomic profiling

Transcriptomic profiling for molecular subtype determination has been described in detail in other syntheses (intrinsic subtypes and PAM50, Lehmann/Pietenpol, Burstein). Clinical applicability of transcriptomic subtype testing in TNBC:

• Prosigna (PAM50) — FDA-cleared but with current clinical-utility focus on HR+ disease. Not routinely used in TNBC.
• TNBCtype (Lehmann/Pietenpol) — web-tool research use; not clinical-grade.
• Burstein subtype calls — research-grade.
• FUSCC subtype calls — used in Chinese clinical trials (FUTURE series).

No transcriptomic subtype assay is FDA-cleared for TNBC treatment decision-making. Use is restricted to clinical trial stratification and academic research.

Practical algorithm for metastatic TNBC profiling

A typical workup at metastatic diagnosis or progression:

1. Confirm/repeat receptor status (ER/PR/HER2 IHC, with HER2 ISH if 2+): particularly if testing relies on archival primary tumor tissue; subtype switching at metastatic recurrence is documented in 5–15% of patients.
2. Germline genetic testing: if not previously done. Multi-gene panel (BRCA1/2 + PALB2 + ATM + CHEK2 + others) preferred over BRCA-only.
3. Tumor genomic profiling: comprehensive panel (FoundationOne CDx, Tempus xT, Caris MI Profile, or institutional equivalent). DNA + RNA-based fusion detection preferred.
4. PD-L1 CPS (22C3) testing: from a recent biopsy. Gates KEYNOTE-355 first-line pembrolizumab.
5. HER2 IHC re-review: particularly for HER2-low identification; the IHC 0 vs 1+ distinction now matters for T-DXd eligibility.
6. Consider ctDNA if tissue is insufficient or for ongoing monitoring.

Evidence table

Open questions and active investigation

• ctDNA-MRD-guided adjuvant treatment decisions. Whether ctDNA-positive status after KEYNOTE-522 should trigger treatment escalation (additional adjuvant agents, additional duration) is being studied prospectively. Positive results could substantially change adjuvant management.
• Combining multi-omic data for treatment selection. Integration of genomic, transcriptomic, IHC, and imaging features into composite predictors of treatment response is an active machine-learning research direction (see ML multimodal fusion synthesis when available).
• Cost-effectiveness of comprehensive panels. Universal NGS at metastatic diagnosis costs $3,000–$5,000 per patient; whether this is cost-effective depends on actionable-finding rates and downstream treatment-decision impact. Real-world economic analyses are accumulating.
• Transcriptomic subtype testing in clinical use. The path to FDA clearance for TNBC-specific transcriptomic subtype assays depends on demonstration of clinical actionability beyond IHC-defined categories. The LAR → AR antagonist pathway is the most plausible near-term opportunity.
• Tissue vs liquid-biopsy heterogeneity. Comparative studies of paired tissue and ctDNA profiles in metastatic TNBC are accumulating; quantifying the situations where they disagree (and why) informs which to trust for each clinical decision.
• Universal germline panel testing. The NCCN recommendation for universal germline testing in TNBC is well-established, but real-world implementation rates vary substantially. Patient-navigation and operational research are addressing the gap.

For the molecular subtyping frameworks underlying transcriptomic profiling, see the intrinsic subtypes synthesis and the Lehmann/Pietenpol synthesis. For PARP inhibitor biology that BRCA testing gates, see the PARP synthesis and the BRCA/HRD synthesis.

References

Each citation links to the original publication via DOI. The same records are searchable in the evidence library by title or DOI.

1. Daly MB, Pal T, Berry MP, et al. NCCN Guidelines Insights: Genetic/Familial High-Risk Assessment: Breast, Ovarian, and Pancreatic, Version 2.2021. J Natl Compr Canc Netw. 2021;19(1):77–102. doi:10.6004/jnccn.2021.0001. ↩
2. Tung NM, Robson ME, Ventz S, et al. TBCRC 048: Phase II Study of Olaparib for Metastatic Breast Cancer and Mutations in Homologous Recombination-Related Genes. J Clin Oncol. 2020;38(36):4274–4282. doi:10.1200/JCO.20.02151. ↩
3. Sicklick JK, Kato S, Okamura R, et al. Molecular profiling of cancer patients enables personalized combination therapy: the I-PREDICT study. Nat Med. 2019;25(5):744–750. doi:10.1038/s41591-019-0407-5. ↩
4. Marabelle A, Le DT, Ascierto PA, et al. Efficacy of Pembrolizumab in Patients With Noncolorectal High Microsatellite Instability/Mismatch Repair-Deficient Cancer: Results From the Phase II KEYNOTE-158 Study. J Clin Oncol. 2020;38(1):1–10. doi:10.1200/JCO.19.02105. ↩

Last reviewed: 2026-06-04. Researcher-layer synthesis page. Evidence grades follow the GRADE-adapted rubric defined at the top of this page.