Trastuzumab

證據等級: L5

預測適應症: 10 個

Trastuzumab: From HER2-Positive Breast Cancer to Normal Breast-Like Subtype of Breast Carcinoma

One-Sentence Summary

Trastuzumab is a HER2-targeted monoclonal antibody originally developed for HER2-positive breast cancer. The TxGNN model predicts it may also be relevant for the normal breast-like subtype of breast carcinoma, but this is currently supported by only 12 clinical trials (mostly indirect, HER2-positive-population trials) and 1 publication (a descriptive/morphological study).

Quick Overview

Item	Content
Original Indication	HER2-positive breast cancer (based on established drug knowledge; not present in the supplied regulatory dataset)
Predicted New Indication	Normal breast-like subtype of breast carcinoma
TxGNN Prediction Score	99.90%
Evidence Level	L2
New Zealand Market Status	✗ Not Marketed
Number of Authorizations	0
Recommended Decision	Hold

Why is This Prediction Reasonable?

Currently, detailed mechanism of action data is not available in the source dataset (flagged as a data gap). Based on known pharmacology, trastuzumab is a humanized monoclonal antibody that binds the extracellular domain of the HER2/neu receptor, inhibiting proliferation of HER2-overexpressing tumor cells and inducing antibody-dependent cellular cytotoxicity (ADCC). Its efficacy in HER2-positive breast cancer is well established, which is the mechanistic basis TxGNN likely used to generate this prediction.

However, "normal breast-like" is a PAM50 intrinsic molecular subtype that is typically characterized by low proliferation and inconsistent — often negative — HER2 expression. This creates a direct mechanistic mismatch: trastuzumab's activity depends on HER2 overexpression, which is not a defining feature of this subtype.

Consistent with this, most of the clinical trials retrieved for this prediction actually enrolled HER2-positive breast cancer populations undergoing neoadjuvant therapy, rather than specifically validating trastuzumab in patients confirmed to have the normal breast-like subtype. The mechanistic link should therefore be regarded as an indirect inference from the broader HER2-positive breast cancer literature, not a direct, subtype-specific validation.

Clinical Trial Evidence

Trial Number	Phase	Status	Enrollment	Key Findings
NCT03168880	Phase 3	Active, not recruiting	720	Randomized comparison of neoadjuvant weekly paclitaxel vs. paclitaxel plus carboplatin in triple-negative breast cancer; large RCT relevant to the basal-like/normal-like subtype context, though not a trastuzumab-specific arm.
NCT01796197	Phase 2	Completed	23	Paclitaxel combined with trastuzumab and pertuzumab as preoperative therapy for inflammatory breast cancer; trastuzumab used directly but not subtype-specific.
NCT04329065	Phase 2	Recruiting	25	WOKVAC vaccine combined with neoadjuvant chemotherapy and HER2-targeted antibody therapy; trastuzumab is background treatment, not the primary study variable.
NCT04759248	Phase 2	Active, not recruiting	55	ATREZZO study — atezolizumab combined with trastuzumab and vinorelbine in ER-negative or PAM50 non-luminal HER2-positive advanced/metastatic breast cancer.
NCT05900206	Phase 2	Recruiting	370	ARIADNE — randomized trial of trastuzumab deruxtecan (an ADC, not the same molecule) vs. standard neoadjuvant treatment with biomarker-driven selection for HER2-positive breast cancer.
NCT06348134	Phase 2	Recruiting	74	Efficacy and safety of optimal neoadjuvant-to-adjuvant anti-HER2-based therapy in Nigerian women with HER2-positive breast cancer.
NCT04750122	Phase 1/2	Recruiting	46	Neoadjuvant therapy guided by in vitro drug screening of patient-derived tumor-like cell clusters for HER2-positive early breast cancer; not a direct efficacy test of trastuzumab in this subtype.
NCT06585969	Phase 3	Withdrawn	0	Trastuzumab deruxtecan vs. CDK4/6 inhibitors in non-Luminal A, ER-positive/HER2-low metastatic breast cancer; trial withdrawn with zero enrollment, provides no evidence.
NCT06328387	Phase 1/2	Unknown	120	Hydroxychloroquine combined with an antibody-drug conjugate vs. ADC alone for advanced breast cancer; mechanistic rationale unclear.
NCT01670877	Phase 2	Completed	56	Neratinib alone and combined with fulvestrant in metastatic HER2 non-amplified but HER2-mutant breast cancer; population definition conflicts with trastuzumab's mechanism of action.

Literature Evidence

PMID	Year	Type	Journal	Key Findings
19466513	2009	Descriptive/Morphology study	Breast cancer (Tokyo, Japan)	Describes morphological and cytopathological features of the basal-like breast carcinoma subtype, situating it among the five DNA-microarray-defined intrinsic subtypes (luminal A, luminal B, normal breast-like, HER2-overexpression, basal-like); does not directly assess trastuzumab efficacy.

New Zealand Market Information

Trastuzumab currently has no marketing authorization on record in New Zealand (market status: Not Marketed; 0 authorizations).

Cytotoxicity

Item	Content
Cytotoxicity Classification	Targeted therapy (HER2-directed monoclonal antibody; not a conventional cytotoxic chemotherapeutic)
Myelosuppression Risk	Low as monotherapy; risk increases when combined with cytotoxic chemotherapy (e.g., taxanes, as seen in several trials above)
Emetogenicity Classification	Low (typical for monoclonal antibody monotherapy)
Monitoring Items	Cardiac function (LVEF/echocardiogram) is the primary monitoring parameter given trastuzumab's known cardiotoxicity risk; infusion-related reaction monitoring; CBC and organ function monitoring when combined with cytotoxic chemotherapy
Handling Protection	Standard biologic/monoclonal antibody handling precautions apply; detailed institutional handling requirements should follow the package insert, as formal safety labeling data is currently a blocking data gap (DG001)

Safety Considerations

Please refer to the package insert for safety information.

Conclusion and Next Steps

Decision: Hold

Rationale: Evidence specific to the normal breast-like subtype is indirect — nearly all identified trials enrolled HER2-positive populations broadly rather than validating efficacy in patients confirmed to have this subtype, and literature support is limited to a single descriptive morphology paper. Since this subtype is typically HER2-low/negative, the mechanistic rationale for trastuzumab is uncertain.

To proceed, the following is needed:

Subtype-specific HER2 expression/amplification data confirming target presence in normal breast-like tumors
TFDA/regulatory safety labeling data (currently a blocking data gap, DG001)
Detailed mechanism of action documentation (currently a data gap, DG002)
A clinical trial or biomarker study that directly stratifies outcomes by PAM50 normal breast-like subtype
Note: within this same evidence pack, the closely related indications progesterone-receptor positive breast cancer and progesterone-receptor negative breast cancer carry substantially stronger evidence (L1, "Proceed with Guardrails") and may warrant separate, prioritized evaluation as the more actionable repurposing opportunities for trastuzumab.
Disclaimer

This content is for research purposes only and does not constitute medical advice. Clinical validation is required before any clinical application.