Why doesn’t this breast cancer fit the standard protocols?

On paper it is a luminal tumor (HR+/HER2−), but ~80% shows neuroendocrine differentiation, with FGFR1 ×13 and CCND1 ×20 amplification. This hybrid subtype (BC-NED) has a worse prognosis and usually needs strategies different from standard luminal breast cancer.

What actionable targets does the tumor have?

The Gallium-68 PET shows somatostatin-receptor subtype 2 (SSTR2) expression, the target of radioligand therapy (PRRT). The molecular profile adds FGFR1 ×13 amplification as a candidate target for FGFR inhibitors.

What is the next step in the case?

A bone rebiopsy with an advanced molecular panel, reviewed by an international tumor board (WIN Consortium), to design an N-of-1 treatment directed at the tumor’s actual biology.

BC-NED + FGFR1 ×13 + SSTR2+

The science behind the case

Luminal breast carcinoma (HR+/HER2−) with ~80% neuroendocrine differentiation (BC-NED), FGFR1 ×13 and CCND1 ×20. Most recent finding: somatostatin receptor subtype 2 (SSTR2) overexpression confirmed by Gallium PET.

Clinical summary

At a glance

The essentials in ten seconds, before the molecular detail.

DiagnosisStage IV: Infiltrating carcinoma (NST) with ~80% neuroendocrine differentiation (BC-NED) · luminal HR+/HER2− · premenopausal · dx January 2024
Molecular driversAmplification: FGFR1 ×13 · CCND1 ×20 · 11q13 cluster (FGF3/FGF4/FGF19 ×18)
Functional targetOpportunity: SSTR2+ on Ga-68 PET → radioligand therapy (PRRT) candidate
Resistance & progressionAcquired: ESR1 D538G · RB1 loss (3 variants in ctDNA) · CDK4/6i resistance
2026 statusECOG 1: ECOG 1 · multiple bone metastases (no visceral involvement) · abemaciclib withdrawn (30 Mar 2026)
Receptors & gradeHR+: ER 95% · PR 5% · HER2 0 (ultralow) · Ki67 60% · G2 (Nottingham) · low TMB and MSI

The thesis: biology, not the organ of origin, should guide treatment.

The anomaly

Why doesn't this tumor fit the protocols?

On paper this is a breast cancer (HR+/HER2−). Under the microscope, ~80% of the tumor shows neuroendocrine differentiation, with and amplification. Spanish protocols recommend treating it as standard luminal and ignoring the component; yet the WHO has recognized breast neuroendocrine neoplasms as a distinct entity since its 2019 classification, and clinical literature shows this hybrid subtype () has worse prognosis and usually needs different strategies.

Tap or hover the highlighted words and markers to see what they mean.

Goal: an N-of-1 trial that sets a precedent for precision oncology in ultra-rare subtypes.

The tumor, in schematic form

One tumor, two faces

It is not one tumor: it is two biologies in the same body, and both must be treated at once.

Receptors: targets to attack (HR and SSTR2). HER2: a receptor she does not have (no target). Amplifications: extra copies that push the tumor. Mutations: resistances the tumor builds to keep growing. RB1: a brake that is being lost. Cg · Syn: neuroendocrine granules (80% of the tumor).

Molecular profile

The tumour’s genomic map

The profile combines primary tissue (NGS, 2024) with plasma ctDNA liquid biopsy (2026). Against a luminal HR+/HER2− background, the standouts are focal amplification of FGFR1 at 11q13, CCND1 and the FGF3/FGF4/FGF19 cluster; each row notes how it was measured.

Detailed molecular profile

TSO500 2024 + IHC + 2026 ctDNA + Ga-68 PET

Alterations, methods and clinical implication

Cross of every available molecular source, with no added interpretation. Each row shows the method by which the result was obtained.

Detailed molecular profile: alteration, result, method/source, category and clinical implication.
Alteration	Result	Method / Source	Category	Clinical implication
FGFR1	Amplified ×13	TSO500 tissue	Luminal driver	CDK4/6i resistance; potential sensitivity to everolimus and to FGFR inhibitors (erdafitinib, futibatinib, ponatinib).
CCND1	Amplified ×20	TSO500 tissue + ctDNA	11q13 cluster	Co-amplified with FGFR1; reinforces CDK4/6i resistance.
FGF3 / FGF4 / FGF19	Amplified ×18	TSO500 tissue	11q13 cluster	Characteristic 11q13 co-amplification; no direct target, marker of aggressive biology.
NE differentiation	~80% (CgA, SYN)	IHC primary tissue	BC-NED subtype	Dominant neuroendocrine behaviour. Justifies exploring NE-tumour therapies (PRRT, platinum regimens).
SSTR2 (somatostatin)	Positive	Ga-68 DOTATOC PET	Radioligand target	Overexpression in bone metastases and focal uptake in the breast. Opens the door to PRRT (radioligand therapy).
Ki67	60%	IHC primary tissue	Grade	High proliferative index. In NEC, Ki67 ≥20% maps to grade 3 ⁺⁺.
ESR1 p.D538G	Detected	ctDNA (Guardant360 + VHIO360, 2026)	Endocrine resistance	Acquired resistance to aromatase inhibitors; entry criterion for the elacestrant trial (ADELA).
RB1	3 variants	ctDNA Guardant360 (Apr 2026)	Resistance / progression	p.V622Yfs33 (1.58%), p.R661W (1.48%) and p.F226 (subclonal); absent in the primary tumour (TSO500, 2024). RB1 loss associated with CDK4/6i resistance and transformation to more aggressive / neuroendocrine phenotypes.
SMO p.V319D	Detected (VUS)	ctDNA (Guardant360 CDx, May 26, 2026)	Uncertain significance	Variant of uncertain clinical significance, under watch.
TMB / MSI	Low / Low	TSO500 tissue	Immunotherapy	No profile for checkpoint inhibitors.
SNVs / INDELs / fusions	None pathogenic	TSO500 tissue	Rest of the panel	No other actionable targets in the original panel.
PIK3CA	Not detected	TSO500 tissue	PI3K target	Pending re-analysis on updated tissue.
HER2	Negative (0)	IHC primary tissue	Receptor	Negative staining; HER2-ultralow present per DIPCAN ⁺.
ER / PR	ER 95% / PR 5%	IHC primary tissue	Hormone receptor	Luminal component of the tumour — basis of the current endocrine line.

Sources and methodological notes

The bone-lesion biopsy (right iliac, April 2026) contained no evaluable tumour —only mineralised bone trabeculae and muscle tissue—, so the molecular profile is read from ctDNA. It is also why the advanced rebiopsy targets the soft-tissue component, where NGS performs far better than in pure bone.

Sources: TSO500 on primary FFPE tissue (DIPCAN, MD Anderson Madrid, 2024) · IHC on primary tissue · Guardant360 / VHIO360 ctDNA (April–May 2026) · Ga-68 DOTATOC PET-CT (Virgen de la Arrixaca, May 2026).

⁺ The HER2-ultralow category (membrane staining in <10% of cells) is present in this case according to data from the DIPCAN study / MD Anderson Madrid.

⁺⁺ In neuroendocrine oncology, Ki67 is the primary grading marker: G1 (<3%), G2 (3–20%), G3 (>20%). A Ki67 of 60% corresponds to a high-grade neuroendocrine carcinoma (NEC G3).

Functional imaging

What the Gallium-68 PET shows

The tracer reveals an actionable target visible in vivo: the tumour expresses , the target of . Standard breast-cancer protocols do not consider this route.

Functional imaging — Gallium-68 PET

Gallium-68 DOTATOC PET-CT

Date:: May 26, 2026

PET with the 68Ga-DOTATOC radiotracer, which binds mainly the somatostatin receptor subtype 2 (SSTR2). Visualizes in vivo which lesions express SSTR2 and could therefore respond to radioligand therapy (PRRT).

«Study showing multiple blastic bone metastases with somatostatin receptor overexpression. Focal uptake in the right breast tail to be evaluated in a dedicated study.»

Clinical meaning: The tumor expresses somatostatin receptors — the target of radioligand therapy (PRRT). It confirms on imaging both tumor drivers (luminal FGFR1/CCND1 + neuroendocrine RB1 + SSTR) and opens a route that breast-cancer protocols do not contemplate as standard.

Clinical history

Treatment history

Each treatment line has held the disease for a while before the tumour escapes again: the pattern to expect when only the hormonal axis is targeted and the neuroendocrine component is left out.

dx
Diagnosis and palliative radiotherapy (January–February 2024)
Completed
Diagnosed in January 2024 after presenting to the ER with low-back pain: vertebral metastases were found. Premenopausal. Palliative systemic treatment started in February 2024 with the goal of prolonging survival. Received radiotherapy to the spine with a good response: progressive improvement, spinal stability and no fractures.
1L
Letrozole + Ribociclib + Zoladex (goserelin) + zoledronic acid
Completed
Ribociclib discontinued after the 1st cycle due to toxicity. Zoladex continued.
2L
Fulvestrant + Abemaciclib + Zoladex (goserelin) + zoledronic acid
Completed
On confirmed progression, letrozole is replaced by fulvestrant and ribociclib by abemaciclib. Zoladex and zoledronic acid are maintained.
→
Bone progression (March 2026)
Completed
The PET-CT (24 Mar 2026) confirms bone progression (increased uptake in pelvis and right femur; new foci in D1 and left iliac). Abemaciclib (always at 100 mg) is stopped on 30 Mar 2026 due to progression and mild hepatotoxicity that normalized once it was withdrawn. Zoladex and zoledronic acid continue. No visceral crisis.
→
Current status (2026)
Active
As a standard 3rd line, elacestrant has been offered (ESR1 route, with public funding approved), pending start. In parallel, she is in screening for two phase 3 trials in HR+/HER2− breast cancer after CDK4/6i: ADELA (elacestrant + everolimus, for her ESR1 mutation) and KATSIS-1 (KAT6 inhibitor + fulvestrant). The first bone rebiopsy (April 2026) did not yield viable tumor, so an extended PET-guided bone rebiopsy is planned — the central test the campaign funds. Functional status: ECOG 1.

Want to dig deeper into the case? Get the full clinical reports —sequencing, ctDNA (VAF) and imaging— in a structured format to review or download.

Get the reports

Therapeutic axes

Where to aim

Several candidate targets follow from all of the above. These are the therapeutic axes the molecular profile points to, each with its own treatment rationale.

How to read these axes

Hypotheses derived from the molecular profile, not a prescribed treatment. The advanced rebiopsy will confirm or rule them out before defining the N-of-1 strategy.

The next step

Bone rebiopsy protocol

A single bone biopsy from which to extract everything current science allows: 13 cores across 6 preservation formats (FFPE, frozen, lysate, OCT, fresh and live tissue). Whatever isn’t processed now is banked to be analysed for 10+ years without re-biopsying. This is what the campaign funds.

Next step (June 2026): bone rebiopsy and fresh ctDNA to confirm how the profile is evolving and prioritise the therapeutic targets.

Proposed bone rebiopsy protocol: component, method and core/format, targets and clinical implication
Component	Method	Targets	Implication
Broad NGS + WGS	≥500-gene panel + WGS · FFPE Core 5 / frozen Core 6	FGFR1-4, CCND1, CDK4, FGF3/4/19, ESR1, PIK3CA, PTEN, RB1, TP53, MET; CNV, TMB, MSI, fusions, SV	Dominant drivers and co-alterations. PTEN and CDK4 reliable only in tissue; CDK4 co-amplified at 11q13 implies CDK4/6i resistance
RNA-seq (expression)	Bulk RNA-seq · frozen Core 6	mRNA FGFR1, FGF3/4/19, MYC; NE signature; PAM50	Better predictor of FGFRi response than amplification alone; confirms the FGFR autocrine circuit
Extended IHC (30)	IHC + RNAscope · FFPE Core 3	ER, PR, HER2 (ultralow), FGFR1, SSTR2, TROP-2, B7-H3, DLL3, CgA, SYN, INSM1, Rb, Cyclin E1, GR	HER2-low→T-DXd · SSTR2→PRRT · DLL3→anti-DLL3 · Cyclin E1 / Rb loss→CDK4/6i resistance
Single-cell Multiome + CITE-seq	snRNA + ATAC, TCR/BCR · frozen Core 7	Transcriptional states + chromatin; ER/HER2/SSTR2/TROP-2/B7-H3/PD-L1; T/B repertoire	NE vs luminal program, resistant clones and immune microenvironment (cold vs hot tumour)
RPPA / phosphoproteomics	~95 proteins · lysate Core 9	p-FRS2α, p-AKT, p-ERK, p-Rb, p-S6, Cyclin E1, GR, p-ER	REAL pathway activation (FGFR, PI3K, MAPK, cell cycle); guides combinations
Spatial transcriptomics	Visium / Xenium · OCT Cores 10–11	Tumour–stroma–bone architecture; is the NE differentiation homogeneous or are there residual HR+ islands?	Determines whether to target only the NE phenotype or also the residual luminal component
Organoids + drug screening	Ex vivo culture · fresh Core 12 / live-cryo Core 13	Ex vivo sensitivity: FGFRi, CDK4/6i, T-DXd, capivasertib, everolimus and combinations	PDOs predict response ~78% and improve PFS when guiding treatment (11.0 vs 5.0 months)
Serial ctDNA	Plasma every 6–8 weeks	FGFR1 amp, ESR1 (Y537S/D538G), PIK3CA, FGFR kinase mutations; tumour fraction ≥1%	Closes the loop: detects resistance 4–8 weeks before imaging, without re-biopsying

Biopsy technical specifications

14G coaxial needle into the peri-lesional soft-tissue component (NGS fails in 36% of pure bone vs 2.3% in soft tissue), ≥20 mm of tissue and ≥20% tumour cellularity confirmed by touch-prep. Serial liquid biopsies close the loop between tissue and real-time therapeutic decisions.

Goal

Goal: N-of-1 Trial

A clinical trial with one patient. Therapeutic decisions are designed on the tumor's actual molecular profile, not on a generic HR+ average. The path: rebiopsy with advanced panel → review at WIN Consortium international MTB → molecularly-directed N-of-1 treatment.

WIN Consortium (Worldwide Innovative Network in Oncology) connects precision-oncology centres of excellence to design individualised diagnostic and therapeutic strategies.

A precedent: precision oncology decided on the patient's molecular data, not on the tumor's label.

Scientific evidence

Key scientific evidence

The peer-reviewed studies and clinical trials that back each hypothesis in the case —FGFR1, PRRT/SSTR, the neuroendocrine transformation and more— gathered on a dedicated page.

See the full evidence

Last updated: 6 June 2026