Synthesis: LAR subtype and androgen-receptor targeting

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.

Why LAR is the most clinically tractable TNBC subtype

Among the various TNBC molecular subtype frameworks (see Lehmann/Pietenpol synthesis and Burstein synthesis), LAR is the most consistent: every major framework identifies a discrete LAR subset characterized by AR pathway activation and luminal differentiation features. Approximately 10–20% of TNBC tumors are LAR, with cohort variation by ancestry (LAR may be more prevalent in Asian cohorts at ~25%).

LAR tumors differ from typical basal-like TNBC in biology and clinical behavior:

• Lower proliferation rates (Ki-67 often 10–30%)
• Frequently apocrine histologic differentiation
• Higher PIK3CA mutation rate (~50%, vs ~10% in basal-like)
• Lower TIL density on average
• Lower pCR rates with standard chemotherapy (10–25%)
• Possibly somewhat indolent natural history compared to basal-like TNBC

The LAR subset's dependence on AR signaling provides a targeted therapeutic opportunity: AR antagonists, originally developed for prostate cancer, have been repurposed for AR-positive TNBC with measurable clinical activity.

AR-IHC operationalization

A persistent operational issue: there is no FDA-cleared companion-diagnostic AR-IHC assay for TNBC, and the threshold for AR-positivity varies across trials. Common thresholds include:

• ≥ 10% AR-positive tumor cell nuclei — the threshold used in the enzalutamide Traina 2018 trial
• ≥ 1% AR-positive nuclei — a broader threshold sometimes used in retrospective analyses
• Allred score ≥ 5 — a quantitative integrated measure used in some pathology reports

AR antibody choice (clones SP107, AR441, others) also affects results. Inter-laboratory standardization of AR-IHC in TNBC is more limited than for ER/PR/HER2; pathology results may not be directly comparable across institutions. As LAR-targeted therapies advance toward regulatory readouts, formal companion-diagnostic development will be needed.

Approximately 25–35% of TNBC tumors are AR-IHC positive at the ≥ 10% threshold — a somewhat larger fraction than the 10–20% of TNBC that is LAR by molecular subtype. The discrepancy reflects that AR expression alone (IHC) doesn't perfectly identify the AR-driven LAR molecular subtype; some AR-positive tumors don't have the full LAR transcriptomic signature, while a few LAR-subtype tumors may have AR expression below the IHC threshold.

TBCRC 011 (bicalutamide, proof-of-concept)

Gucalp and colleagues conducted a phase II single-arm trial of bicalutamide 150 mg daily in 26 patients with AR-positive (≥ 10% nuclear AR-IHC), ER/PR-negative metastatic breast cancer^[1]C. The trial enrolled both HER2-negative (predominantly TNBC) and HER2-positive AR-positive disease.

• Clinical benefit rate (CR + PR + SD ≥ 6 months): 19% (5/26 patients)
• Median PFS: 12 weeks
• Safety: Well-tolerated; gynecomastia and hot flashes were the most common AEs.

TBCRC 011 established proof-of-concept for AR antagonism in AR-positive TNBC and is the foundational trial of this targeted-therapy class. The trial was too small for definitive efficacy conclusions but motivated subsequent investigation with more potent AR antagonists.

Traina 2018 (enzalutamide)

Traina and colleagues conducted a phase II single-arm trial of enzalutamide 160 mg daily in 118 patients with AR-positive (defined by Dx1 diagnostic test ≥ 10% AR-IHC) metastatic TNBC^[2]B. Enzalutamide is a more potent AR antagonist than bicalutamide, originally developed for castration-resistant prostate cancer.

• 16-week clinical benefit rate (Dx1+): 25% (74-evaluable patients)
• 24-week clinical benefit rate: 20%
• Median PFS (Dx1+): 14.7 weeks (~3.4 months)
• Median OS (Dx1+): 17.6 months
• Safety: Fatigue, nausea most common; consistent with prostate-cancer experience

The trial also developed a "PREDICT AR" gene-expression signature that further enriched for benefit beyond AR-IHC alone — patients positive for both IHC and the gene-expression predictor had higher response rates. The signature has not advanced to clinical adoption but informs ongoing trial design.

Enzalutamide's activity in this trial confirmed proof-of-concept and produced clinical-benefit rates substantially above the 5–10% typically seen for any single agent in heavily pre-treated metastatic TNBC. Phase III randomized confirmation has not been completed.

TBCRC 032 (enzalutamide + taselisib)

Lehmann and colleagues conducted a phase IB/II trial of enzalutamide combined with the PI3K-alpha inhibitor taselisib in AR+ metastatic TNBC, motivated by the high prevalence of PIK3CA mutations in the LAR subtype^[3]B.

• Clinical benefit rate: 36%
• PIK3CA-mutated subset clinical benefit: higher than wild-type
• Safety: Tolerable but with PI3K-class-specific toxicities (hyperglycemia, diarrhea, rash)

The result reinforced the biological rationale for combining AR antagonism with PI3K pathway inhibition in LAR/AR+ TNBC. Taselisib's development was discontinued for unrelated reasons (regulatory and commercial), but the proof-of-principle motivated subsequent combination trials with other PI3K inhibitors.

Current trial landscape

Several ongoing trials are testing AR antagonists and AR-pathway-directed combinations in TNBC:

• Enobosarm — a selective AR modulator (SARM) with tissue-selective AR-agonist or antagonist activity. Being tested in AR+ breast cancer (both HR+ and TNBC). The mechanism differs from pure AR antagonists; activity in TNBC is hypothesis-generating.
• Darolutamide — another potent AR antagonist with prostate-cancer approval. Phase II trials in AR+ TNBC ongoing.
• AR antagonist + CDK4/6 inhibitor combinations — rationale: LAR's low proliferation rate may make it CDK4/6-sensitive, and AR-pathway inhibition could augment this. Several trials testing palbociclib or other CDK4/6 inhibitors plus AR antagonist in LAR-subtype TNBC.
• AR antagonist + PARP inhibitor — rationale: BRCAness signatures appear elevated in a subset of AR+ TNBC, suggesting PARP-inhibitor sensitivity in this subset. Early-phase data are mixed.
• AR antagonist + immunotherapy — rationale: AR-pathway activity may modulate the immune microenvironment. Early-phase data are exploratory.
• FUTURE series (China) — biomarker-stratified TNBC trials using FUSCC subtypes, including LAR-specific AR antagonist + PI3K inhibitor arms. Preliminary results suggest improved response over historical controls.

Practical considerations in 2026

In current US/EU clinical practice, AR antagonists are not routinely used for metastatic TNBC outside of clinical trials. Reasons:

• No phase III trial has demonstrated AR antagonist benefit at a level supporting regulatory approval for TNBC.
• Standard first/second-line metastatic options (pembrolizumab + chemo, PARP inhibitor, sacituzumab, T-DXd, chemotherapy) cover most patients in the early-line setting.
• AR-IHC testing is not routinely performed at metastatic recurrence; the LAR-targeted-therapy option is not surfaced in standard biomarker-testing workflows.

For patients with heavily pre-treated metastatic TNBC who have exhausted standard options, AR-IHC testing and consideration of clinical trial enrollment for AR-targeted therapy is reasonable. Off-label use of enzalutamide outside of a trial is occasionally pursued but not standard.

Evidence table

Open questions and active investigation

• Phase III randomized confirmation. The most consequential gap. Despite a decade of proof-of-concept data, no phase III RCT has confirmed AR antagonist benefit at a level supporting routine clinical adoption in TNBC. Whether a definitive phase III will be funded depends on pharmaceutical-sponsor interest, which has been variable.
• Optimal biomarker selection. AR-IHC, AR gene-expression signatures (PREDICT AR), LAR molecular subtyping — multiple approaches exist; harmonization and head-to-head comparison would clarify which is the best clinical predictor.
• Combination strategies. The TBCRC 032 enzalutamide + taselisib signal, the AR + CDK4/6 inhibitor rationale, and the AR + immunotherapy rationale all motivate combinations that haven't been definitively tested in randomized trials.
• Earlier-line vs late-line AR antagonist use. Most data are from pre-treated metastatic patients. Whether earlier-line use (first-line metastatic or even neoadjuvant in LAR-subtype) would produce different magnitudes of benefit is unknown.
• HR+/AR+/HER2− vs ER−/AR+/HER2−. AR antagonism in HR+ breast cancer (where ER is the dominant pathway) is a separate question. Whether AR antagonism could benefit HR+/AR+ patients who progress on endocrine therapy is being tested.
• Acquired resistance mechanisms. AR antagonist resistance in prostate cancer involves AR splice variants (AR-V7), AR amplification, and AR mutations. Whether analogous mechanisms drive resistance in TNBC and whether they could be circumvented (selective AR degraders, SARMs) is investigational.

For the LAR subtype's place in the broader molecular taxonomy, see the Lehmann/Pietenpol synthesis and the Burstein synthesis. For the first-line metastatic decision tree where LAR consideration would currently sit (as a clinical-trial option), see the first-line metastatic 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. Gucalp A, Tolaney S, Isakoff SJ, et al. Phase II trial of bicalutamide in patients with androgen receptor-positive, estrogen receptor-negative metastatic breast cancer (TBCRC 011). Clin Cancer Res. 2013;19(19):5505–5512. doi:10.1158/1078-0432.CCR-12-3327. ↩
2. Traina TA, Miller K, Yardley DA, et al. Enzalutamide for the treatment of androgen receptor-expressing triple-negative breast cancer. J Clin Oncol. 2018;36(9):884–890. doi:10.1200/JCO.2016.71.3495. ↩
3. Lehmann BD, Abramson VG, Sanders ME, et al. TBCRC 032 IB/II Multicenter Study: molecular insights to AR antagonist and PI3K inhibitor efficacy in patients with AR+ metastatic triple-negative breast cancer. Clin Cancer Res. 2020;26(9):2111–2123. doi:10.1158/1078-0432.CCR-19-2170. ↩
4. Bonnefoi H, Grellety T, Tredan O, et al. A phase II trial of abiraterone acetate plus prednisone in patients with triple-negative androgen receptor positive locally advanced or metastatic breast cancer (UCBG 12-1). Ann Oncol. 2016;27(5):812–818. doi:10.1093/annonc/mdw067. ↩
5. Jiang YZ, Liu Y, Xiao Y, et al. Molecular subtyping and genomic profiling expand precision medicine in refractory metastatic triple-negative breast cancer: the FUTURE trial. Cell Res. 2021;31(2):178–186. doi:10.1038/s41422-020-0375-9. ↩

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