> Trialight public data. Index of pages: https://trialight.com/llms.txt
> Web page: https://trialight.com/data/asset/letrozole-67319198-7e88-4130-b185-d776c835863c
> Record changed: 2026-10-13

# Letrozole

Highest phase reached

Approved

Source: [www.ebi.ac.uk](https://www.ebi.ac.uk/chembl/explore/compound/CHEMBL1444)

Drug type

Small molecule

Source: [www.ebi.ac.uk](https://www.ebi.ac.uk/chembl/explore/compound/CHEMBL1444)

First approval year

1997

Source: [www.ebi.ac.uk](https://www.ebi.ac.uk/chembl/explore/compound/CHEMBL1444)

## Development status

**First approval year**

1997

Source: [www.ebi.ac.uk](https://www.ebi.ac.uk/chembl/explore/compound/CHEMBL1444)

**Listing at source**

Listed

**Highest phase reached**

Approved

Source: [www.ebi.ac.uk](https://www.ebi.ac.uk/chembl/explore/compound/CHEMBL1444)

## Names and chemistry

**Drug type**

Small molecule

Source: [www.ebi.ac.uk](https://www.ebi.ac.uk/chembl/explore/compound/CHEMBL1444)

**Drug name**

Letrozole

Source: [www.ebi.ac.uk](https://www.ebi.ac.uk/chembl/explore/compound/CHEMBL1444)

**Molecular weight**

285.31

Source: [www.ebi.ac.uk](https://www.ebi.ac.uk/chembl/explore/compound/CHEMBL1444)

**Structure (SMILES)**

N#Cc1ccc(C(c2ccc(C#N)cc2)n2cncn2)cc1

Source: [www.ebi.ac.uk](https://www.ebi.ac.uk/chembl/explore/compound/CHEMBL1444)

### Brand names (6)

- femara
- Femara
- letrozole
- Letrozole
- letrozole component of kisqali femara co pack
- Letrozole component of kisqali femara co-pack

### Other names (60)

- Aromatase Inhibitors (Femara)
- cgs 20267
- CGS 20267
- CGS-20267
- cgs20267
- CGS20267
- Femara
- Femara (Sequence 1)
- Femara (Sequence 2)
- Femara® Tablets 2.5 mg
- kisqali femara co pack component letrozole
- Kisqali femara co-pack component letrozole
- letrozol
- Letrozol
- letrozole
- Letrozole
- Letrozole (2.5 mg)
- Letrozole (aromatase inhibitor)
- Letrozole (Aromatase Inhibitors)
- letrozole (Femara)
- Letrozole (Femara)
- Letrozole \[EP IMPURITY\]
- Letrozole \[EP MONOGRAPH\]
- Letrozole \[HSDB\]
- Letrozole \[INN\]

And 35 more, listed on the interactive page.

## Identifiers

**ATC classification codes**

- L02BG04

Sources for recorded values

Source: [www.ebi.ac.uk](https://www.ebi.ac.uk/chembl/explore/compound/CHEMBL1444)

**CAS registry numbers**

- 112809-51-5

**ChEMBL ID**

CHEMBL1444

Source: [www.ebi.ac.uk](https://www.ebi.ac.uk/chembl/explore/compound/CHEMBL1444)

**InChIKey**

HPJKCIUCZWXJDR-UHFFFAOYSA-N

Source: [www.ebi.ac.uk](https://www.ebi.ac.uk/chembl/explore/compound/CHEMBL1444)

**PubChem compound IDs**

- 3902

**RxNorm IDs (RxCUI)**

- 72965

**FDA ingredient codes (UNII)**

- 7LKK855W8I

## Regulatory information

### United States

**Applicant**

NOVARTIS PHARMS

**Approval date**

25 Jul 1997

**Application number**

NDA020726

### Other regulatory facts

**First in class**

No

**Orphan designation**

No

**Availability**

Prescription only

## Pharmacology

### Drug classification

**Pharmacology name**

letrozole

**Type**

Synthetic organic

**Drug name stem**

\-rozole

**Approval recorded by Guide to Pharmacology**

Yes

#### Administration routes

- Oral

### Mechanisms of action (2)

- **Action**  
Inhibition

**Action type**  
Inhibitor

**Target**  
CYP19A1

**Gene symbol**  
CYP19A1

**Protein identifier**  
P11511

**Median affinity**

10.7

**Affinity units**  
pKi

**Primary target**  
Yes
- **Mechanism**  
Cytochrome P450 19A1 inhibitor

**Action type**  
Inhibitor

**Target**  
Aromatase

**Protein identifier**  
P11511

### Open Targets mechanisms

- **Mechanism**  
Cytochrome P450 19A1 inhibitor

**Action type**  
Inhibitor

**Target**  
Aromatase

### DrugCentral mechanisms

- **Action type**  
Inhibitor

**Gene symbol**  
CYP19A1

**Protein identifier**  
P11511

**Organism**  
Homo sapiens

**Target development level**  
Clinical

### Investigated indications (51)

- **Condition**  
Azoospermia

**Highest recorded phase**  
3

**Condition identifier**  
EFO:0000279

**Subject identifier**  
D053713
- **Condition**  
Breast Neoplasms

**Highest recorded phase**  
4

**Condition identifier**  
EFO:0000305

**Subject identifier**  
D001943
- **Condition**  
Carcinoma

**Highest recorded phase**  
2

**Condition identifier**  
EFO:0000313

**Subject identifier**  
D002277
- **Condition**  
Carcinoma, Intraductal, Noninfiltrating

**Highest recorded phase**  
3

**Condition identifier**  
EFO:0000432

**Subject identifier**  
D002285
- **Condition**  
Carcinoma, Endometrioid

**Highest recorded phase**  
1

**Condition identifier**  
EFO:0000466

**Subject identifier**  
D018269
- **Condition**  
Infertility

**Highest recorded phase**  
3

**Condition identifier**  
EFO:0000545

**Subject identifier**  
D007246
- **Condition**  
Carcinoma, Lobular

**Highest recorded phase**  
2

**Condition identifier**  
EFO:0000553

**Subject identifier**  
D018275
- **Condition**  
Leiomyosarcoma

**Highest recorded phase**  
2

**Condition identifier**  
EFO:0000564

**Subject identifier**  
D007890
- **Condition**  
Mesothelioma

**Highest recorded phase**  
1

**Condition identifier**  
EFO:0000588

**Subject identifier**  
D008654
- **Condition**  
Neoplasms

**Highest recorded phase**  
4

**Condition identifier**  
EFO:0000616

**Subject identifier**  
D009369
- **Condition**  
Polycystic Ovary Syndrome

**Highest recorded phase**  
3

**Condition identifier**  
EFO:0000660

**Subject identifier**  
D011085
- **Condition**  
Leiomyoma

**Highest recorded phase**  
1

**Condition identifier**  
EFO:0000731

**Subject identifier**  
D007889
- **Condition**  
Endometriosis

**Highest recorded phase**  
2

**Condition identifier**  
EFO:0001065

**Subject identifier**  
D004715
- **Condition**  
Ovarian Neoplasms

**Highest recorded phase**  
3

**Condition identifier**  
EFO:0001075

**Subject identifier**  
D010051
- **Condition**  
Uterine Cervical Neoplasms

**Highest recorded phase**  
2

**Condition identifier**  
EFO:0001416

**Subject identifier**  
D002583
- **Condition**  
Pregnancy

**Highest recorded phase**  
3

**Condition identifier**  
EFO:0002950

**Subject identifier**  
D011247
- **Condition**  
Carcinoma, Non-Small-Cell Lung

**Highest recorded phase**  
1

**Condition identifier**  
EFO:0003060

**Subject identifier**  
D002289
- **Condition**  
Brain Neoplasms

**Highest recorded phase**

0.5

**Condition identifier**  
EFO:0003833

**Subject identifier**  
D001932
- **Condition**  
Uterine Neoplasms

**Highest recorded phase**  
2

**Condition identifier**  
EFO:0003859

**Subject identifier**  
D014594
- **Condition**  
Breast Neoplasms

**Highest recorded phase**  
4

**Condition identifier**  
EFO:0003869

**Subject identifier**  
D001943
- **Condition**  
Osteoporosis

**Highest recorded phase**  
3

**Condition identifier**  
EFO:0003882

**Subject identifier**  
D010024
- **Condition**  
Hemangiosarcoma

**Highest recorded phase**  
2

**Condition identifier**  
EFO:0003968

**Subject identifier**  
D006394
- **Condition**  
Endometrial Neoplasms

**Highest recorded phase**  
3

**Condition identifier**  
EFO:0004230

**Subject identifier**  
D016889
- **Condition**  
Infertility, Male

**Highest recorded phase**  
2

**Condition identifier**  
EFO:0004248

**Subject identifier**  
D007248
- **Condition**  
Triple Negative Breast Neoplasms

**Highest recorded phase**  
2

**Condition identifier**  
EFO:0005537

**Subject identifier**  
D064726

And 26 more, listed on the interactive page.

### Open Targets indications (111)

- **Condition identifier**  
EFO\_0000279

**Highest recorded phase**  
3
- **Condition identifier**  
EFO\_0000305
- **Condition identifier**  
EFO\_0000313

**Highest recorded phase**  
2
- **Condition identifier**  
EFO\_0000466
- **Condition identifier**  
EFO\_0000545

**Highest recorded phase**  
3
- **Condition identifier**  
EFO\_0000564

**Highest recorded phase**  
2
- **Condition identifier**  
EFO\_0000616
- **Condition identifier**  
EFO\_0000660

**Highest recorded phase**  
3
- **Condition identifier**  
EFO\_0000731

**Highest recorded phase**  
1
- **Condition identifier**  
EFO\_0001065

**Highest recorded phase**  
2
- **Condition identifier**  
EFO\_0001073

**Highest recorded phase**  
3
- **Condition identifier**  
EFO\_0001075

**Highest recorded phase**  
3
- **Condition identifier**  
EFO\_0001416

**Highest recorded phase**  
2
- **Condition identifier**  
EFO\_0002950

**Highest recorded phase**  
2
- **Condition identifier**  
EFO\_0002950

**Highest recorded phase**  
3
- **Condition identifier**  
EFO\_0003869

**Highest recorded phase**  
3
- **Condition identifier**  
EFO\_0003882

**Highest recorded phase**  
3
- **Condition identifier**  
EFO\_0004230

**Highest recorded phase**  
2
- **Condition identifier**  
EFO\_0004248

**Highest recorded phase**  
2
- **Condition identifier**  
EFO\_0008509

**Highest recorded phase**  
1
- **Condition identifier**  
EFO\_0008587

**Highest recorded phase**  
3
- **Condition identifier**  
EFO\_0009708

**Highest recorded phase**  
2
- **Condition identifier**  
EFO\_0009870

**Highest recorded phase**  
2
- **Condition identifier**  
EFO\_1000649
- **Condition identifier**  
EFO\_1000954

And 86 more, listed on the interactive page.

### Reported adverse events (25)

- **Event**  
alopecia

**Reports**  
646

**Reporting signal score**

509.018
- **Event**  
arthralgia

**Reports**  
1,414

**Reporting signal score**

795.511
- **Event**  
bone lesion

**Reports**  
72

**Reporting signal score**

161.889
- **Event**  
bone pain

**Reports**  
500

**Reporting signal score**

585.225
- **Event**  
breast cancer

**Reports**  
747

**Reporting signal score**  
1,391.56
- **Event**  
breast cancer metastatic

**Reports**  
706

**Reporting signal score**  
2,438.56
- **Event**  
breast cancer recurrent

**Reports**  
219

**Reporting signal score**

657.867
- **Event**  
carbohydrate antigen 15-3 increased

**Reports**  
99

**Reporting signal score**

371.326
- **Event**  
disease progression

**Reports**  
792

**Reporting signal score**

777.549
- **Event**  
fatigue

**Reports**  
1,457

**Reporting signal score**

271.366
- **Event**  
hot flush

**Reports**  
583

**Reporting signal score**

833.928
- **Event**  
leukopenia

**Reports**  
288

**Reporting signal score**

268.802
- **Event**  
malignant neoplasm progression

**Reports**  
1,697

**Reporting signal score**  
3,458.5
- **Event**  
metastases to bone

**Reports**  
950

**Reporting signal score**  
2,829.77
- **Event**  
metastases to liver

**Reports**  
751

**Reporting signal score**  
2,074.1
- **Event**  
metastases to lung

**Reports**  
361

**Reporting signal score**

878.689
- **Event**  
metastases to lymph nodes

**Reports**  
279

**Reporting signal score**

718.928
- **Event**  
metastases to skin

**Reports**  
58

**Reporting signal score**

186.183
- **Event**  
metastases to spine

**Reports**  
119

**Reporting signal score**

318.403
- **Event**  
neoplasm progression

**Reports**  
783

**Reporting signal score**  
1,678.37
- **Event**  
neutropenia

**Reports**  
1,390

**Reporting signal score**  
1,407.43
- **Event**  
pik3ca-activated mutation

**Reports**  
95

**Reporting signal score**

399.317
- **Event**  
second primary malignancy

**Reports**  
158

**Reporting signal score**

259.77
- **Event**  
tumour marker increased

**Reports**  
166

**Reporting signal score**

418.476
- **Event**  
white blood cell count decreased

**Reports**  
318

**Reporting signal score**

187.282

### Trial references (327)

- NCT00003140  
Source: [clinicaltrials.gov](https://clinicaltrials.gov/study/NCT00003140)
- NCT00004205  
Source: [clinicaltrials.gov](https://clinicaltrials.gov/study/NCT00004205)
- NCT00014638  
Source: [clinicaltrials.gov](https://clinicaltrials.gov/study/NCT00014638)
- NCT00084396  
Source: [clinicaltrials.gov](https://clinicaltrials.gov/study/NCT00084396)
- NCT00090857  
Source: [clinicaltrials.gov](https://clinicaltrials.gov/study/NCT00090857)
- NCT00101062  
Source: [clinicaltrials.gov](https://clinicaltrials.gov/study/NCT00101062)
- NCT00107263  
Source: [clinicaltrials.gov](https://clinicaltrials.gov/study/NCT00107263)
- NCT00134680  
Source: [clinicaltrials.gov](https://clinicaltrials.gov/study/NCT00134680)
- NCT00161291  
Source: [clinicaltrials.gov](https://clinicaltrials.gov/study/NCT00161291)
- NCT00171314  
Source: [clinicaltrials.gov](https://clinicaltrials.gov/study/NCT00171314)
- NCT00171704  
Source: [clinicaltrials.gov](https://clinicaltrials.gov/study/NCT00171704)
- NCT00171847  
Source: [clinicaltrials.gov](https://clinicaltrials.gov/study/NCT00171847)
- NCT00194779  
Source: [clinicaltrials.gov](https://clinicaltrials.gov/study/NCT00194779)
- NCT00199134  
Source: [clinicaltrials.gov](https://clinicaltrials.gov/study/NCT00199134)
- NCT00208273  
Source: [clinicaltrials.gov](https://clinicaltrials.gov/study/NCT00208273)
- NCT00237133  
Source: [clinicaltrials.gov](https://clinicaltrials.gov/study/NCT00237133)
- NCT00237224  
Source: [clinicaltrials.gov](https://clinicaltrials.gov/study/NCT00237224)
- NCT00238290  
Source: [clinicaltrials.gov](https://clinicaltrials.gov/study/NCT00238290)
- NCT00238316  
Source: [clinicaltrials.gov](https://clinicaltrials.gov/study/NCT00238316)
- NCT00241046  
Source: [clinicaltrials.gov](https://clinicaltrials.gov/study/NCT00241046)
- NCT00247650  
Source: [clinicaltrials.gov](https://clinicaltrials.gov/study/NCT00247650)
- NCT00248170  
Source: [clinicaltrials.gov](https://clinicaltrials.gov/study/NCT00248170)
- NCT00265759  
Source: [clinicaltrials.gov](https://clinicaltrials.gov/study/NCT00265759)
- NCT00280930  
Source: [clinicaltrials.gov](https://clinicaltrials.gov/study/NCT00280930)
- NCT00290745  
Source: [clinicaltrials.gov](https://clinicaltrials.gov/study/NCT00290745)

And 302 more, listed on the interactive page.

## Dosing

**Dose**

2.5mg

**Route**

Oral

**How often**

Once daily

## Chemical properties

**Hydrogen bond acceptors**

5

**Hydrogen bond donors**

0

**Polar surface area**

78.29

**Calculated partition coefficient (ALogP)**

2.66

**Calculated partition coefficient (XLogP)**

2.7

**Prodrug**

No

**Chirality**

Achiral

**Inorganic**

No

**Rule-of-five violations**

0

**Rotatable bonds**

3

**Heavy atoms**

22

**Molecular formula**

C17H11N5

**Monoisotopic mass**

285.10144537

**Natural product**

Yes

## National Drug Codes

- 0078-0249
- 0093-7620
- 16729-034
- 23155-875
- 24979-726
- 42291-374
- 50268-476
- 51407-986
- 51991-759
- 55111-646
- 59651-180
- 62135-491
- 71205-587
- 80005-139
- 17856-0032
- 50090-3474
- 50090-8002
- 63629-7819
- 63850-0025
- 68071-2167
- 68071-5264
- 69117-0004
- 71335-1526
- 71335-2396

## Evidence counts

**Recorded assays**

2,570

**Active assays**

116

### Active assay types (4)

- Confirmatory
- Other
- Screening
- Summary

## Pharmacologic actions

- Antineoplastic Agents  
Source: [id.nlm.nih.gov](https://id.nlm.nih.gov/mesh/D000970.html)
- Aromatase Inhibitors  
Source: [id.nlm.nih.gov](https://id.nlm.nih.gov/mesh/D047072.html)

## Biological measurements

### Observed measurements

#### Oral bioavailability

**Median**

99.9

**Mean**

99.9

**Minimum**

99.9

**Maximum**

99.9

**Unit**

%

**Assays**

1

**Standard deviation**

0

**Summary method**

median

**Censored results excluded**

0

**Other units excluded**

0

**Unknown units excluded**

0

#### Measurement types

- F

## Related records

### Trials (756)

- A 2-Week Ketogenic Diet in Combination With Letrozole to Modulate PI3K Signaling in ER+ Breast Cancer
- A 5-treatment, Study in Healthy Volunteers to Assess The Safety, Tolerability, and Pharmacokinetics of Four Controlled Release (CR) Pregabalin Tablet Formulations and the Immediate Release (IR) Formulation Administered Fasted
- A Clinical Study of Darcilil Combined With AI Combined With Pyrrotinib in the Treatment of TPBC
- A Clinical Study of HRS-6209 Combined With Other Treatment Regimens in Patients With Breast Cancer
- A Clinical Study to Evaluate the Safety and Efficacy of JHM03 in Adult Patients With Upper Limb Spasticity
- A Clinical Trial to Compare Efficacy and Tolerability of Atorvastatin in Addition to Endocrine Treatment With Focus on Mechanisms of Resistance to Endocrine Treatment (Fulvestrant/Aromatase Inhibitors) in Patients With Advanced Breast Cancer
- A Companion Sample Collection Protocol to Support the Discovery of Breast Cancer Aberrations With Treatment of CDK4/6 Therapy/LEE011/Ribociclib
- A Comparison of Letrozole and Clomifene Citrate
- A Dose Escalation Study Evaluating the Safety and Tolerability of GDC-0032 in Participants With Locally Advanced or Metastatic Solid Tumors or Non-Hodgkin's Lymphoma (NHL) and in Combination With Endocrine Therapy in Locally Advanced or Metastatic Hormone Receptor-Positive Breast Cancer
- A New Oral Treatment For Type II Diabetes Mellitus
- A Open Study of Metronomic Oral Vinorelbine in Combination With Aromatase Inhibitors for the Treatment of Postmenopausal Women With Hormone Receptor Positive,HER2-negative, Advanced Breast Cancer Who Received no Prior Therapy for Advanced Disease
- A Pharmacodynamics Pre-surgical Study of LEE011 in Early Breast Cancer Patients (MONALEESA-1)
- A Phase 2 Single-Arm Open-Label Pilot Trial Evaluating Zanidatamab (ZW25) in Patients With Early Stage HER2/Neu Positive (HER2+) Breast Cancer (BC)
- A Phase 3 Study of HRS-8080 Versus Treatment Chosen by Physicians in Locally Advanced and Metastatic Breast Cancer
- A Phase I/II Study of XZP-3287 in Metastasis Solid Tumors
- A Phase Ib Dose Escalation Study of the Combination of LEE011 With Letrozole and Dose Expansion of LEE011 With Hormonal Therapy for the Treatment of Pre-(With Goserelin) and Postmenopausal Women With Hormone Receptor Positive, HER2-negative, Advanced Breast Cancer
- A Phase Ib Study of GB491 Plus Letrozole in Patients With Advanced Breast Cancer
- A Phase II Clinical Study to Evaluate HLX43 in Subjects With Advanced Non-small Cell Lung Cancer (NSCLC)
- A Phase II Clinical Study to Evaluate HLX43 in Subjects With Advanced Pancreatic Cancer
- A Phase II Randomized Study Evaluating the Biological and Clinical Effects of the Combination of Palbociclib With Letrozole as Neoadjuvant Therapy in Post-Menopausal Women With Estrogen-Receptor Positive Primary Breast Cancer

### Approved for (5)

- [Breast cancer](https://trialight.com/data/condition/breast-cancer-8ac10da3-93bd-54c5-a93b-265bc6699689.md)
- Breast carcinoma
- [Breast neoplasm](https://trialight.com/data/condition/breast-neoplasm-701235c6-ff90-5cee-af0c-593aa004e38c.md)
- [Cancer](https://trialight.com/data/condition/cancer-703b1dfc-4812-50eb-83f4-d7a205d16bdb.md)
- Neoplasm

### In development for (43)

- Adenomyosis Phase 2
- Angiosarcoma Phase 2
- Anovulation Phase 2
- [Brain neoplasm](https://trialight.com/data/condition/brain-neoplasm-b3dac71b-1d7b-5a65-8f64-89821506ad41.md) Early phase 1
- Breast lobular carcinoma Phase 2
- [Carcinoma](https://trialight.com/data/condition/carcinoma-575e4c82-5fa5-5455-b1b7-30972eca1a2f.md) Phase 2
- [Cervical adenocarcinoma](https://trialight.com/data/condition/cervical-adenocarcinoma-013a4346-286c-5c50-bd25-66fde59ac6a0.md) Phase 2
- Ductal breast carcinoma in situ Phase 3
- Ectopic pregnancy Phase 1
- [Endometrial cancer](https://trialight.com/data/condition/endometrial-cancer-4da2a0bc-7943-502b-a698-cc2beccbed8c.md) Phase 3
- [Endometrial carcinoma](https://trialight.com/data/condition/endometrial-carcinoma-d0794a04-ff16-5af6-8fb7-7b3d6bd6c537.md) Phase 3
- Endometrioid adenocarcinoma Phase 1
- [Endometriosis](https://trialight.com/data/condition/endometriosis-3a5471b6-6d24-50b8-b1e6-8803dd78b0db.md) Phase 2
- [Fallopian tube cancer](https://trialight.com/data/condition/fallopian-tube-cancer-b95d05ee-41d5-565a-87e1-041170b88760.md) Phase 2
- Fallopian tube carcinoma Phase 2
- Female breast carcinoma Phase 3
- Hereditary breast ovarian cancer syndrome Phase 3
- Hermansky-Pudlak syndrome Phase 2
- Hypogonadotropic hypogonadism Phase 3
- Infertility disorder Phase 3

### Other linked conditions (3)

- Estrogen-receptor positive breast cancer
- Gestational trophoblastic neoplasm
- Habitual spontaneous abortion

### Targets (1)

- [CYP19A1](https://trialight.com/data/target/cyp19a1-9682b33b-ed66-55a7-8155-bf00584059c7.md) Cytochrome P450 19A1 inhibitor

---

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