Does IGF-1 Increase Cancer Risk? The Scientific Evidence

Higher circulating levels of insulin-like growth factor 1 (IGF-1) are consistently linked to a modestly increased risk of several common cancers, with the strongest evidence pointing to prostate, breast, and colorectal malignancies. A large UK Biobank analysis of hundreds of thousands of participants found that each 5 nmol/L increase in circulating IGF-1 raised overall cancer risk by about 3% in both men and women.¹ That number sounds small on its own, but it scales across wide ranges of IGF-1 concentration, and it conceals sharper associations with specific tumor types. The picture also has a counterintuitive twist: very low IGF-1 does not appear protective against dying from cancer either, and in people who already have certain tumors, higher IGF-1 can predict better outcomes.

What the Largest Cohort Studies Show

Two of the most informative datasets on this question come from the UK Biobank and the EPIC-Heidelberg cohort. In the UK Biobank study, researchers measured IGF-1 in blood samples from over 390,000 participants and followed them for cancer diagnoses. The 3% rise in cancer risk per 5 nmol/L increment held for both sexes, but the association was more pronounced for certain sites.¹ The EPIC-Heidelberg analysis, drawn from a European prospective cohort, found direct links between higher IGF-1 and risk of both breast cancer (about 25% higher for those in the upper range) and prostate cancer (about 31% higher).²

These are observational findings, meaning they measure association rather than proving that IGF-1 directly caused anyone’s tumor. But the consistency across large, well-designed studies gives the association real weight, and newer genetic methods (discussed below) have begun to test whether the link is causal.

Prostate Cancer Has the Most Consistent Signal

Of all cancer types studied, prostate cancer has accumulated the deepest body of evidence tying it to IGF-1. An early landmark case-control study found that men with higher IGF-1 had roughly 50% greater odds of prostate cancer per 100 ng/mL increase in IGF-1, and men under 70 faced nearly triple the risk.³ That individual study was later reinforced by a large meta-analysis pooling individual-level data from multiple cohorts. Men in the top fifth of IGF-1 concentration had about 29% higher odds of prostate cancer compared to men in the bottom fifth when the analysis was limited to prospective studies, with a clear dose-response trend.⁴

The relationship appears linear: the higher the IGF-1, the higher the risk, without a clear threshold below which the association disappears. The signal is robust enough that it has held up across populations and study designs over more than two decades of investigation.

Breast and Colorectal Cancers

Breast cancer shows a similar pattern, though with some nuance by menopausal status. A pooled analysis of 17 prospective studies found that women in the highest fifth of IGF-1 had 28% higher odds of breast cancer compared to women in the lowest fifth. The association was stronger for postmenopausal women, where the odds ratio for the linear trend was about 1.30.⁵ For premenopausal women, the link was weaker and barely reached significance. The reason for this difference is not fully settled, but the interplay between estrogen, insulin, and IGF-1 signaling in the breast likely plays a role.

Colorectal cancer is the other site with strong observational data. A recent meta-analysis found that people with colorectal cancer had significantly higher circulating IGF-1 levels than healthy controls, and the association extended to precancerous colorectal lesions as well.⁶ A separate study found that people in the top quarter of IGF-1 had 80% higher odds of advanced colorectal adenomas, the precursors to cancer, compared to the bottom quarter.⁷ That the association shows up in pre-malignant polyps, not just established cancers, is a strong hint that IGF-1 acts early in the disease process.

How IGF-1 Promotes Tumor Growth at a Cellular Level

IGF-1 is a growth hormone mediator. Its normal job is to stimulate cells to grow, divide, and survive, which is exactly what you want during childhood development and tissue repair. But those same signals become dangerous in cells that are already on the path toward becoming cancerous. IGF-1 promotes cell proliferation and migration, supports the formation of new blood vessels that tumors need to expand, and inhibits programmed cell death, the built-in self-destruct mechanism that normally eliminates damaged or abnormal cells.⁸ IGF-1 also cross-talks with insulin signaling. People with obesity or type 2 diabetes tend to have elevated insulin, which in turn drives up IGF-1 activity, creating what amounts to a chronic pro-growth environment.⁹

Beyond promoting the initial growth of tumors, IGF-1 signaling can also help cancers resist treatment. Research has shown that the IGF-1 receptor pathway contributes to resistance against both standard chemotherapy and newer targeted therapies, making tumors harder to kill once they have formed.¹⁰

Is the Link Causal? Evidence From Genetics

Observational studies always leave room for doubt. People with high IGF-1 differ from people with low IGF-1 in many ways: body composition, diet, physical activity, other hormones. So researchers have turned to Mendelian randomization, a method that uses inherited genetic variants linked to IGF-1 levels as a kind of natural experiment. Because genes are assigned at random at conception, genetic variants that predict higher lifetime IGF-1 should not be confounded by lifestyle in the way blood measurements are.

The results from this approach are mixed, and that is an important part of the story. A large Mendelian randomization study using data from the UK Biobank and BioBank Japan found the strongest causal signal for colorectal cancer. People genetically predisposed to higher IGF-1 had 11% to 22% greater odds of colorectal cancer, depending on the cohort. For prostate and breast cancer, the genetic evidence was weaker and inconsistent across datasets.¹¹ A separate Mendelian randomization analysis focused on breast cancer did find that a genetically predicted 5 nmol/L increase in IGF-1 raised breast cancer risk by about 5%, with the association driven by estrogen-receptor-positive tumors.¹²

The takeaway is that for colorectal cancer, there is reasonably solid genetic evidence pointing to a causal role for IGF-1. For breast and prostate cancer, the causal case is suggestive but not airtight. The genetic effect sizes are generally smaller than what observational studies find, which is common: it suggests that some of the observational association is genuinely causal, while some reflects shared lifestyle factors or reverse causation.

Laron Syndrome and the Zero-Cancer Population

Perhaps the most striking evidence comes not from a study design but from a rare genetic condition. People with Laron syndrome have a mutation in the growth hormone receptor gene, which means their bodies produce almost no IGF-1 throughout their entire lives. They are short in stature and have distinctive physical features, but they have another remarkable characteristic: they essentially do not develop cancer. Multiple epidemiological analyses of Laron syndrome populations have confirmed this near-complete cancer protection.¹³¹⁴

This is as close to a natural knockout experiment as human biology allows. It does not prove that moderately lowering IGF-1 in healthy people would reduce cancer risk, because the Laron population has near-zero IGF-1 from birth, which is a fundamentally different biological state from someone with levels in the normal range. But it confirms that IGF-1 signaling is deeply involved in whether human cells can become malignant.

The U-Shaped Mortality Problem

If the story ended at “higher IGF-1 means more cancer,” the practical advice would be straightforward: lower your IGF-1 as much as possible. But the data complicate that prescription. The EPIC-Heidelberg cohort revealed a U-shaped relationship between IGF-1 and death from cancer, cardiovascular disease, and all causes. Participants with the lowest levels of IGF-1 also experienced higher mortality, not just those at the top.²

This makes biological sense. IGF-1 is not a toxin. It maintains muscle mass, supports bone density, aids wound healing, and plays roles in brain health. People with abnormally low IGF-1, whether from malnutrition, chronic illness, or advanced age, tend to be frail and metabolically compromised. That frailty itself can worsen cancer outcomes by limiting treatment tolerance. The sweet spot appears to be a middle range of IGF-1: high enough to support normal tissue maintenance, low enough to avoid chronically fueling cell proliferation. Where exactly that range falls for any individual is still poorly defined.

Diet, Protein, and IGF-1 Levels

Your circulating IGF-1 is not fixed. It responds to what you eat. Higher protein intake is one of the most consistent dietary drivers of IGF-1. A study of people with type 2 diabetes found that a high-protein diet increased IGF-1 by about 14%, regardless of whether the protein came from animal or plant sources.¹⁵ That finding challenges the popular belief that plant protein is inherently “safer” for IGF-1 levels than animal protein. A larger observational analysis did find that higher animal protein intake was associated with higher IGF-1 and lower levels of certain binding proteins that keep IGF-1 in check, while plant protein was also associated with higher IGF-1 but with simultaneously higher levels of one protective binding protein (IGFBP-1).¹⁶

The practical upshot is that total protein intake matters more than whether it comes from steak or lentils, at least when it comes to raw IGF-1 numbers. However, the binding protein profile around IGF-1 also matters: what ultimately drives cellular signaling is not total IGF-1 in the blood but the fraction that is biologically active and free to bind receptors. Animal protein appears to shift that balance slightly more toward free, active IGF-1. A mouse study comparing matched protein diets found that animals fed plant protein had lower serum IGF-1 than those fed animal protein, and developed fewer ovarian tumors.¹⁷ Translating mouse tumor models directly to human cancer risk is always uncertain, but the direction aligns with the observational human data.

Exercise Raises IGF-1 in Healthy People but Lowers It in Cancer Patients

The relationship between physical activity and IGF-1 contains one of the more fascinating paradoxes in this field. A systematic review and meta-analysis found that exercise significantly raised IGF-1 in healthy individuals by an average of about 21 ng/mL. In people with cancer, exercise did the opposite: it lowered IGF-1 by roughly 15 ng/mL.¹⁸ In both groups, exercise also increased levels of IGFBP-3, a binding protein that sequesters IGF-1 and reduces its free, active fraction.

This bidirectional effect helps explain why exercise consistently lowers cancer risk despite acutely raising a hormone linked to cancer. In a healthy body, the IGF-1 bump from exercise reflects normal anabolic adaptation: muscles are repairing and growing. The simultaneous rise in binding proteins keeps the growth signals appropriately contained. In someone with cancer, the metabolic environment is different, and exercise appears to shift the IGF-1 system in a direction that is less favorable to tumor growth. The lesson is that IGF-1 levels alone, without accounting for binding proteins and tissue context, give an incomplete picture of cancer risk.

Growth Hormone Therapy and Cancer Concerns

Recombinant human growth hormone (GH) therapy raises IGF-1 levels by design. It is prescribed primarily for children with growth hormone deficiency, but also for certain adult conditions. Because IGF-1 has such potent cell-growth-promoting effects, the question of whether GH therapy increases cancer risk has been debated for decades.¹⁹

The Pediatric Endocrine Society’s assessment of the evidence concluded that GH can be used in growth-hormone-deficient childhood cancer survivors who are in remission, with the understanding that GH therapy may increase their risk of developing second, unrelated cancers. For children who already have medical conditions that predispose them to malignancies, the decision requires careful individual evaluation and ongoing surveillance.²⁰ In healthy children treated for simple growth hormone deficiency, the evidence has not shown a clear increase in first-time cancer risk, though long-term follow-up data remain limited.

When Higher IGF-1 Predicts Better Cancer Outcomes

Here is where the narrative gets especially counterintuitive. While elevated IGF-1 is associated with developing cancer in the first place, once a person already has certain cancers, higher IGF-1 at diagnosis can actually predict better survival. In renal cell carcinoma, patients with higher genetically predicted IGF-1 had a 26% lower risk of death and a 19% lower risk of recurrence compared to patients with lower IGF-1.²¹ In advanced liver cancer, patients with high baseline IGF-1 receiving anti-angiogenic therapy had a median overall survival of nearly 11 months, compared to about 4 months for patients with low IGF-1.²²

This is not as contradictory as it seems. The liver produces most of the body’s circulating IGF-1, and a very low IGF-1 level in a cancer patient often signals severe liver dysfunction, poor nutritional status, or advanced systemic disease. In that context, low IGF-1 is a marker of how sick the patient already is, not a sign that the cancer is less aggressive. The IGF-1 story, in other words, depends heavily on timing and context: higher levels may contribute to getting cancer in the first place, while the same marker in an already-sick person reflects physiological reserve rather than tumor-promoting activity.

Why Anti-IGF Drugs Have Mostly Disappointed

Given all the evidence linking IGF-1 to cancer, pharmaceutical companies invested heavily in drugs targeting the IGF-1 receptor (IGF-1R) during the 2000s and early 2010s. More than ten inhibitors entered clinical trials, including monoclonal antibodies that block the receptor and small-molecule drugs that inhibit its signaling. The results were largely disappointing. In a phase III trial of figitumumab combined with chemotherapy in advanced lung cancer, the drug did not improve progression-free or overall survival. Another antibody, dalotuzumab, failed similarly in metastatic colon cancer, with patients receiving the drug actually faring slightly worse than those on placebo.²³ Development of both drugs was abandoned.

A few bright spots emerged. Some patients with Ewing sarcoma and thymoma showed dramatic, sustained responses to IGF-1R antibodies.²⁴ But the broader failure across common adult tumors has forced a rethink. The IGF-1 receptor shares structural features and signaling pathways with the insulin receptor, so blocking one can inadvertently activate the other. Tumors are also adept at switching to alternative survival pathways when one route is blocked. The current consensus is that IGF-1R remains a valid target in selected tumor types, but success depends on identifying biomarkers that predict which patients will respond, and on designing drug combinations that cut off the escape routes tumors use.²⁵

What About Other Cancer Sites

The IGF-1 and cancer story has focused disproportionately on prostate, breast, and colorectal cancers because that is where the data are richest. For many other cancer types, the evidence is thin or absent. The Mendelian randomization study that tested IGF-1 against 14 additional site-specific cancers (including lung, ovarian, bladder, and several others) found no statistically significant association for any of them.¹¹ For esophageal cancer, one nested case-control study found that the ratio of IGF-1 to its binding protein IGFBP-3 was more informative than IGF-1 alone, but the association between free IGF-1 and esophageal cancer risk was not statistically significant after adjusting for confounders like smoking and alcohol.²⁶

The absence of evidence for other cancers does not mean IGF-1 plays no role in them. IGF-1 receptors are expressed on the surface of most human cell types, and the growth-promoting machinery is universal. But the epidemiological signal for lung cancer, ovarian cancer, and many rarer tumors is either too noisy or has not been studied in large enough populations to draw firm conclusions. It is possible that IGF-1’s influence on these cancers is real but too small to detect with current study sizes, or that other risk factors (smoking for lung, BRCA mutations for ovarian) simply overwhelm any IGF-1 contribution.

The Binding Protein Layer

One reason the IGF-1 story resists simple answers is that IGF-1 does not float through the bloodstream alone. Most of it travels bound to a family of six binding proteins, with IGFBP-3 being the most abundant. These proteins act as a buffer system, controlling how much free IGF-1 is available to bind receptors and trigger cell growth. Time-restricted eating, for example, did not significantly lower total IGF-1 in one randomized trial, but it did raise levels of IGFBP-2, a binding protein associated with reduced IGF-1 activity, and lowered the ratio of IGF-1 to IGFBP-3 relative to controls.²⁷

This means that two people with the same total IGF-1 level can have very different amounts of biologically active IGF-1, depending on their binding protein profile. Standard blood tests report total IGF-1, which is what most of the epidemiological research is based on. But the free fraction is likely what matters most for cancer risk, and it is harder to measure and less commonly tested. Researchers have increasingly argued that future studies need to account for the full IGF system, not just the headline number, to understand who is truly at elevated risk.

1
PubMed Central. Circulating Insulin-Like Growth Factor-1 and Risk of Total and Site-specific Cancers: Cohort Study Analyses from the UK Biobank
2
The Journal of Clinical Endocrinology & Metabolism. IGF-1 and Risk of Morbidity and Mortality From Cancer, Cardiovascular Diseases, and All Causes in EPIC-Heidelberg
3
PubMed. Insulin-like growth factor 1 and prostate cancer risk: a population-based, case-control study
4
Cancer Research. A Meta-analysis of Individual Participant Data Reveals an Association between Circulating Levels of IGF-I and Prostate Cancer Risk
5
PubMed Central. Insulin-like growth factor 1 (IGF1), IGF binding protein 3 (IGFBP3), and breast cancer risk: pooled individual data analysis of 17 prospective studies
6
PubMed Central. Circulating protein levels of insulin-like growth factor 1 signaling pathway and the predisposition to colorectal carcinogenesis: a systematic review and meta-analysis
7
PubMed Central. Serum IGF1, IGF2 and IGFBP3 and risk of advanced colorectal adenoma
8
PubMed Central. Insulin-like growth factor-1 signaling in the tumor microenvironment: Carcinogenesis, cancer drug resistance, and therapeutic potential
9
PubMed Central. The proliferating role of insulin and insulin-like growth factors in cancer
10
PubMed Central. Insulin-like growth factor receptor signaling in tumorigenesis and drug resistance: a challenge for cancer therapy
11
PubMed Central. Insulin-like growth factor-1 and site-specific cancers: A Mendelian randomization study
12
PubMed Central. Insulin-like growth factor-1, insulin-like growth factor-binding protein-3, and breast cancer risk: observational and Mendelian randomization analyses with ∼430 000 women
13
PubMed Central. Genome-Wide Profiling of Laron Syndrome Patients Identifies Novel Cancer Protection Pathways
14
PubMed. Differential expression of IGFBPs in Laron syndrome-derived lymphoblastoid cell lines: Potential correlation with reduced cancer incidence
15
PubMed Central. Similar dietary regulation of IGF-1- and IGF-binding proteins by animal and plant protein in subjects with type 2 diabetes
16
PubMed Central. Association of animal and plant protein intakes with biomarkers of insulin and insulin-like growth factor axis
17
PubMed Central. The effect of the type of dietary protein on the development of ovarian cancer
18
PubMed Central. Exercise-induced modulation of IGF-1 in healthy, obese, and cancer populations: a systematic review and meta-analysis
19
PubMed Central. Risk of cancer in patients treated with recombinant human growth hormone in childhood
20
The Journal of Clinical Endocrinology & Metabolism. Risk of Neoplasia in Pediatric Patients Receiving Growth Hormone Therapy—A Report From the Pediatric Endocrine Society Drug and Therapeutics Committee
21
PubMed Central. Prognostic significance of circulating insulin growth-like factor 1 and insulin growth-like factor binding protein 3 in renal cell carcinoma patients
22
Clinical Cancer Research. Serum Insulin-Like Growth Factor-1 Levels Predict Outcomes of Patients with Advanced Hepatocellular Carcinoma Receiving Antiangiogenic Therapy
23
Genes & Diseases. Drugging IGF-1R in cancer: New insights and emerging opportunities
24
PubMed Central. IGF-1R as an anti-cancer target–trials and tribulations
25
PubMed Central. Molecular Pathways: Clinical Applications and Future Direction of Insulin-like Growth Factor-1 Receptor Pathway Blockade
26
PubMed Central. Insulin-like growth factor-1, IGF binding protein-3, and the risk of esophageal cancer in a nested case-control study
27
PubMed Central. Effect of Time-Restricted Eating on Circulating Levels of IGF1 and Its Binding Proteins in Obesity: An Exploratory Analysis ofer a Randomized Controlled Trial