Letrozole

證據等級: L5

預測適應症: 10 個

Letrozole: From Breast Cancer to Female Breast Carcinoma

One-Sentence Summary

Letrozole is a third-generation aromatase inhibitor whose established clinical role — per the literature captured in this evidence pack — is hormone receptor-positive breast cancer in postmenopausal women. TxGNN’s top-ranked signal is Female Breast Carcinoma (score 99.98%), backed by 50 clinical trials and 20 publications, but this evidence set largely reflects letrozole’s already-known indication rather than a genuinely novel repurposing target — Australian regulatory (ARTG) records and the drug’s original-indication field are both currently blank in this dataset.

Quick Overview

Item	Content
Original Indication	Not recorded in ARTG data in this pack; literature describes letrozole as an established hormone receptor-positive (HR+) breast cancer therapy (PMID 20095792, 36243120)
Predicted New Indication	Female Breast Carcinoma
TxGNN Prediction Score	99.98%
Evidence Level	L1
Australia Market Status	Not marketed (per current data)
Number of ARTG Entries	0
Recommended Decision	Proceed with Guardrails

Why is This Prediction Reasonable?

Detailed DrugBank mechanism-of-action data is not available for this candidate. Based on the literature retrieved in this evidence pack, letrozole is a third-generation, non-steroidal aromatase inhibitor: it blocks conversion of adrenal androgens to oestrogens, lowering circulating oestrogen levels and thereby slowing the growth of oestrogen-dependent tumours (PMID 20095792).

The overlap between letrozole’s known use and the “predicted” indication here is important to flag transparently. Female breast carcinoma is the disease area letrozole is globally best known for treating, and several trials/publications in the supporting evidence (e.g. NCT01740427/PALOMA‑2, NCT00754845/MA.17 extension) are large, long-established registration or post-marketing studies rather than exploratory repurposing trials. The evidence pack’s own annotation for the closely related “estrogen-receptor positive breast cancer” candidate (rank 5) makes this explicit: “letrozole 直接切斷腫瘤生長驅動因子，機轉高度吻合，屬其核心已驗證適應症而非新假說” (mechanistically well matched — this is a core, already-validated indication rather than a new hypothesis).

Practical implication: this candidate should be read as confirmatory, high-confidence evidence for letrozole in breast cancer, not as a novel repurposing signal. Because the original-indication field and Australian ARTG record are both empty in this dataset, a formal comparison against letrozole’s currently approved Australian indication cannot yet be completed — this needs to be closed before any guardrailed use decision is finalised.

Clinical Trial Evidence

Trial Number	Phase	Status	Enrolment	Key Findings
NCT02600923	Phase 3	Completed	131	Palbociclib + letrozole in HR+/HER2- postmenopausal advanced breast cancer (Latin America access study)
NCT02338310	Phase 3	Active, not recruiting	4,486	Large perioperative aromatase-inhibitor trial in postmenopausal HR+ breast cancer, with Ki67 as a recurrence predictor
NCT01740427	Phase 3	Completed	666	PALOMA-2: palbociclib + letrozole vs placebo + letrozole as first-line therapy in ER+/HER2- advanced breast cancer
NCT00754845	Phase 3	Completed	1,918	Extended adjuvant letrozole vs placebo after 5 years of prior aromatase-inhibitor therapy (MA.17-related)
NCT00171340	Phase 3	Completed	1,065	Zoledronic acid timing for prevention of letrozole-associated bone loss in adjuvant therapy
NCT00171704	Phase 3	Completed	263	Letrozole vs tamoxifen — effects on bone and lipid metabolism in resected HR+ early breast cancer
NCT02278120	Phase 3	Completed	672	Ribociclib vs placebo with tamoxifen/NSAI + goserelin in premenopausal HR+/HER2- advanced breast cancer
NCT03056755	Phase 2	Completed	383	BYLieve: alpelisib + fulvestrant or letrozole in PIK3CA-mutant HR+/HER2- advanced breast cancer
NCT00310180	Phase 3	Active, not recruiting	10,273	TAILORx — Oncotype DX-guided hormone therapy ± chemotherapy in node-negative ER+ breast cancer
NCT06223698	Phase 3	Not yet recruiting	3,832	SWE-Switch: extended adjuvant endocrine therapy strategy comparison in high-risk luminal breast cancer

No ANZCTR-registered trial identifiers were found in the supplied evidence.

Literature Evidence

PMID	Year	Type	Journal	Key Findings
32683565	2020	RCT	Breast Cancer Res Treat	PALOMA-1 overall survival: palbociclib + letrozole vs letrozole alone in first-line ER+/HER2- advanced breast cancer
16382061	2005	RCT	New England Journal of Medicine	Letrozole vs tamoxifen as adjuvant therapy in postmenopausal HR+ early breast cancer
35464999	2022	Cohort/Comparative	Comput Math Methods Med	Efficacy/safety/prognosis of sequential tamoxifen–letrozole vs letrozole monotherapy
36243120	2022	Review	Life Sciences	Overview of letrozole pharmacology, toxicity, and therapeutic effects, including its aromatase-inhibitor mechanism
20095792	2010	Review	Expert Opin Drug Metab Toxicol	Pharmacodynamics, pharmacokinetics, clinical efficacy and safety of letrozole
15001182	2004	Review	Women’s Health Issues	Clinical implications and remaining questions from the Letrozole Breast Cancer Trial
35378469	2022	Cohort	Current Problems in Cancer	Predictive response/prognostic factors for palbociclib + letrozole in HR+ advanced breast cancer
34645649	2022	Biomarker study	Clin Cancer Res	Biomarkers of response/resistance to palbociclib + letrozole in ER+/HER2- breast cancer
16500235	2006	Review	Breast (Edinburgh)	Development of letrozole and its use in advanced and neoadjuvant breast cancer
27235140	2016	Preclinical	Med Oncol	Letrozole-induced changes in carcinoma-associated fibroblasts affecting endocrine therapy efficacy

Cytotoxicity

Letrozole is an antineoplastic agent by virtue of its cancer indication, but it is a hormonal (endocrine) therapy, not a conventional cytotoxic chemotherapeutic.

Item	Content
Cytotoxicity Classification	Targeted/hormonal therapy — non-steroidal aromatase inhibitor (not conventional cytotoxic chemotherapy)
Myelosuppression Risk	Low — aromatase inhibitors are not typically myelosuppressive; formal toxicity data was not available in this evidence pack
Emetogenicity Classification	Low
Monitoring Items	Bone mineral density and lipid profile (per supporting trial endpoints), liver function; formal PI-based monitoring guidance is a data gap
Handling Protection	Standard oral oncology medication precautions; not generally subject to injectable cytotoxic handling protocols, but confirm against institutional policy and the TGA-approved PI

Safety Considerations

Please refer to the TGA-approved Product Information (PI) for safety information. No key warnings, contraindications, or drug–drug interaction data were returned for letrozole in this evidence pack (DDI query status: not found).

Conclusion and Next Steps

Decision: Proceed with Guardrails

Rationale: Multiple large, completed Phase 3 trials and RCT-grade literature strongly support letrozole’s efficacy in HR+ breast cancer, giving this candidate L1 evidence strength. However, this appears to largely confirm an already-known indication rather than reveal a new one, and two data-pack-flagged gaps remain unresolved: TFDA/ARTG product and indication data is rated a Blocking gap (prevents formal safety pre-assessment), and detailed mechanism-of-action data is rated High severity.

To proceed, the following is needed:

TGA/ARTG regulatory record confirmation for letrozole (current data shows 0 entries / not marketed, which should be verified against the real ARTG register)
Formal comparison of letrozole’s currently approved Australian indication against “Female Breast Carcinoma” to confirm whether this is a genuinely new use or an evidence-pack labelling gap
DrugBank/PI mechanism-of-action and safety data (key warnings, contraindications, DDI) to complete the S1 safety pre-assessment referenced in the Blocking data gap (DG001)
Disclaimer

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