Letter of Support Initiative

What is a Letter of Support?

This is a letter issued to a requester that briefly describes CDER’s thoughts on the potential value of a biomarker and encourages further evaluation. This letter does not connote qualification of a biomarker. It is meant to enhance the visibility of the biomarker, encourage data sharing, and stimulate additional studies.

Why Issue a Letter of Support?

Encouraging the identification of promising new drug development tools is a recognized approach to overcome hurdles in drug development. The intent of the LOS is to enhance the visibility of a promising biomarker, demonstrate the FDA’s support for the development of the biomarker and encourage collaborative efforts. When issued, both the LOS and the requester’s contact information are made publicly available on the LOS Initiative Website.

How to Request a Letter of Support?

An LOS request should be submitted electronically to DrugDevelopmentTools@fda.hhs.gov and contain the content elements and a draft letter of support described in the documents below. In response to a request, we will set up a meeting to discuss the appropriateness of the proposed LOS with the requester and provide next steps.

Information and Templates:

For more information, please contact DrugDevelopmentTools@fda.hhs.gov


Issued Letters of Support

Area(s) for Use in Drug Development
Issuance Date with Link to Letter of Support
Requester Contact

Critical Path Institute's (C-Path) Predictive Safety Testing Consortium (PSTC), Nephrotoxicity Working Group (NWG)

Urinary Biomarkers: Osteopontin and Neutrophil Gelatinase-associated Lipocalin (NGAL)

Early Clinical Drug Development

8/20/2014: Letter of Support (PDF)

Refer to Predictive Safety Testing Consortiumdisclaimer icon Web Site

C-Path, PSTC, Skeletal Muscle Working Group (SMWG)

Serum and Plasma Biomarkers: Myosin Light Chain 3 (Myl3), Skeletal Muscle Troponin I (sTNI),  Fatty Acid Binding Protein 3 (FABP3), Creatine Kinase, Muscle Type (CK-M, the Homodimer CK-MM)

Early Clinical Drug Development

1/22/2015: Letter of Support (PDF)

Refer to Predictive Safety Testing Consortiumdisclaimer icon Web Site

C-Path, Coalition Against Major Diseases Consortium (CAMD)

Cerebral Spinal Fluid (CSF) Analyte Biomarkers: Aβ1-42, Total tau, Phosphotau

Exploratory Prognostic Biomarkers for Enrichment in Early Stage Alzheimer’s Disease Clinical Trials

2/26/2015: Letter of Support (PDF)

Refer to Coalition Against Major Diseasesdisclaimer icon Web Site

C-Path, CAMD

Magnetic Resonance Imaging Biomarker: Low Baseline Hippocampal Volume

Exploratory Prognostic Biomarkers for Enrichment in Early Stage Alzheimer's Disease Clinical Trials

3/10/2015: Letter of Support (PDF)

Refer to Coalition Against Major Diseasesdisclaimer icon Web Site

C-Path, CAMD

Molecular Neuroimaging Biomarker: Dopamine Transporter (DAT)

Exploratory Prognostic Biomarkers for Enrichment in Early Stage Parkinson's Disease Clinical Trials

3/16/2015: Letter of Support (PDF)

Refer to Coalition Against Major Diseasesdisclaimer icon Web Site

C-Path, Polycystic Kidney Disease (PKD) Outcomes Consortium

MRI, Computerized Tomography (CT), or Ultrasound (US) Biomarker: Total Kidney Volume (TKV)

Exploratory Prognostic Biomarker for Enrichment in Autosomal Dominant Polycystic Kidney

4/23/2015: Letter of Support (PDF)

Refer to Polycystic Kidney Disease Outcomes Consortiumdisclaimer icon Web Site

Memorial Sloan-Kettering Cancer Center, Medivation Inc., and Janssen Diagnostics, LLC

Circulating Tumor Cell (CTC) Enumeration

Disease Activity Biomarker for use in Metastatic Castration-resistant Prostate Cancer (mCRPC)

9/25/2015: Letter of Support (PDF)

Debra J. Rasmussen 

Xhale, Inc.

2-Butanone in Human Breath

Monitoring Biomarker to Evaluate Drug-Dosing Compliance on a Dose-by-Dose Basis

11/19/2015: Letter of Support (PDF)

Donn Dennis


Functional Respiratory Imaging (FRI) of Lung and Airway Structural and Functional Parameters Measured by Low-dose High-definition Volumetric Computerized Tomography (HDCT) Scans and Quantitative Imaging Technology

Prognostic Biomarkers of Disease Progression and Pharmacodynamic Response for use in Idiopathic Pulmonary Fibrosis (IPF)  

6/6/2016: Letter of Support (PDF) 

Jan De Backer


(Urinary Peptide Panel)

Prognostic Enrichment Biomarker Panel for use in Early Stage Diabetic Kidney Disease 

6/14/2016: Letter of Support (PDF) 

Harald Mischak

The Safer and Faster Evidence-based Translation Consortium (SAFE-T)

Cytokeratin 18 (CK‐18), Total and Hyperacetylated High Mobility Group Protein B1 (HMGB1), Osteopontin, and Macrophage Colony-Stimulating Factor 1 Receptor (CSF1R)

Exploratory Monitoring Biomarkers for Use in Drug Development as a Clinical Safety Assessment of the Risk of Drug-induced Liver Injury (DILI) Progression

7/25/2016: Letter of Support (PDF)

Drs. Gerd Kullak-Ublick, Sif Ormarsdottir, John-Michael Sauer or Douglas Keller or view either the Critical Path Institute Website or the IMI SAFE-T Consortium Website


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