Unit Converter
ProGRP – Progastrin-releasing peptide
(High-specificity Tumor Marker for Small Cell Lung Cancer - Useful in Diagnosis, Monitoring & Relapse Detection)
Synonyms
- ProGRP
- Pro–gastrin releasing peptide
- Pro-bombesin
- ProGRP(31–98) / ProGRP(1–125) (assay-specific fragments)
- SCLC tumor marker
Units of Measurement
- pg/mL
- pg/dL
- pg/100 mL
- pg%
- pg/L
- ng/L
Unit Relationships
1 pg/mL=1000 pg/L1\ \text{pg/mL} = 1000\ \text{pg/L}1 pg/mL=1000 pg/L 1 ng/L=1 pg/mL1\ \text{ng/L} = 1\ \text{pg/mL}1 ng/L=1 pg/mL 1 pg/mL=100 pg/dL1\ \text{pg/mL} = 100\ \text{pg/dL}1 pg/mL=100 pg/dL \text{pg%} = \text{pg/dL}
Description
ProGRP is a stable precursor peptide of gastrin-releasing peptide (GRP), a neuroendocrine hormone.
It serves as a highly specific circulating tumor marker for Small Cell Lung Cancer (SCLC).
Why ProGRP instead of GRP?
- GRP is unstable (rapidly degraded).
- ProGRP is stable, circulates longer, and is measurable with reliable immunoassays.
Produced mainly by:
- Neuroendocrine cells
- Small cell lung carcinoma cells (major)
- Certain other neuroendocrine tumors (rare)
Physiological Role
GRP stimulates:
- Gastrin release
- Gastrointestinal motility
- Neuroendocrine signaling
ProGRP has no significant direct physiological role; it is a surrogate marker of neuroendocrine activity and tumor production.
Clinical Significance
HIGH ProGRP
(Strong indicator of SCLC)
1. Small Cell Lung Cancer (Primary Use)
- Elevated in >80% of SCLC cases.
- Levels correlate with:
- Tumor burden
- Metastatic spread
- Treatment response
- Relapse risk
- Tumor burden
2. Differentiating SCLC vs Non–Small Cell Lung Cancer (NSCLC)
- NSCLC rarely elevates ProGRP.
- Helps when biopsy is difficult or inconclusive.
3. Neuroendocrine Tumors
Mild elevation in:
- Medullary thyroid cancer
- Gastroenteropancreatic neuroendocrine tumors
- Merkel cell carcinoma
4. Renal Failure
ProGRP is partly cleared by kidneys → levels rise as eGFR drops.
→ Always interpret with kidney function.
LOW / NORMAL ProGRP
- Healthy individuals
- Non–neuroendocrine lung cancers (adenocarcinoma, squamous)
- Viral or bacterial infections
- Benign lung conditions
- COPD, asthma, pneumonia
A normal ProGRP does not rule out SCLC completely → some limited-stage cases have normal levels.
Reference Intervals
(Tietz 8E + Mayo + ARUP + Oncology Guidelines)
Adults (non-smokers)
- < 60 pg/mL
Smokers
- < 80 pg/mL
(Slightly higher baseline)
Diagnostic Cutoffs
- > 100 pg/mL → suspicious, repeat test & evaluate
- > 200 pg/mL → strongly suggestive of SCLC
- > 300–500 pg/mL → high likelihood of extensive-stage SCLC
- > 1000 pg/mL → very high tumor burden or metastasis
Renal Failure Adjustment
- eGFR <60 can elevate ProGRP to 80–200 pg/mL
- eGFR <30 can elevate to >300 pg/mL
→ Use tumor trends, not single values.
Diagnostic Uses
1. Diagnosis of Small Cell Lung Cancer
Best used with:
- NSE (Neuron-specific enolase)
- Imaging (CT/PET)
- Cytology/biopsy
2. Monitoring Treatment Response
Falling ProGRP = good chemotherapy response
Persistent elevation = residual disease or chemoresistance
3. Detecting Relapse
ProGRP rises weeks before imaging changes appear.
4. Distinguishing SCLC from NSCLC
Very high specificity when:
- ProGRP > 200 pg/mL
- NSE elevated mildly
5. Assessing Neuroendocrine Tumor Burden
Analytical Notes
- Immunoassays (e.g., chemiluminescent assays)
- Stable in serum/plasma for several days refrigerated
- Not affected by hemolysis or lipemia significantly
- Renal impairment is the biggest confounder
- Separate serum from clot promptly
Clinical Pearls
- ProGRP + NSE improves diagnostic accuracy for SCLC.
- Very high levels (>300 pg/mL) strongly suggest SCLC even before biopsy.
- Renal failure elevates ProGRP disproportionately - check eGFR before interpreting.
- A rising ProGRP trend is more meaningful than a single elevated value.
- Excellent for detecting relapse months before symptoms.
Interesting Fact
ProGRP is so stable that preserved samples can remain analyzable for days - unlike NSE, which is unstable and rises with hemolysis, making ProGRP far more reliable as a tumor marker.
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Tumor Markers
- IASLC Lung Cancer Biomarker Guidelines
- Mayo Clinic Laboratories - ProGRP
- ARUP Consult - Lung Cancer Biomarkers
- NCCN SCLC Guidelines
- NIH / MedlinePlus - Tumor Marker Tests