Can Testogel cause cancer? This is a common concern for men considering or currently using testosterone replacement therapy. Testogel is a transdermal testosterone gel prescribed for confirmed hypogonadism in men with abnormally low testosterone levels. Whilst the relationship between testosterone therapy and cancer risk—particularly prostate cancer—has been extensively studied, current evidence does not support a causal link between Testogel and cancer development in men without pre-existing disease. However, appropriate screening, monitoring, and clinical vigilance remain essential components of safe testosterone replacement therapy. This article examines the evidence surrounding Testogel and cancer risk, alongside important safety considerations.

What Is Testogel and How Does It Work?

Testogel is a transdermal testosterone gel prescribed for testosterone replacement therapy (TRT) in men with confirmed hypogonadism—a condition characterised by abnormally low testosterone levels. The gel contains testosterone as the active ingredient and is applied daily to clean, dry skin. For Testogel 50 mg (1% sachets), application sites include shoulders, upper arms, or abdomen, while Testogel 16.2 mg/g should only be applied to shoulders and upper arms. Once applied, the testosterone is absorbed through the skin into the bloodstream, where it supplements the body's natural hormone production.

The mechanism of action involves testosterone binding to androgen receptors in various tissues throughout the body. This hormonal activity supports multiple physiological functions, including maintenance of muscle mass and bone density, regulation of libido and sexual function, production of red blood cells, and influence on mood and cognitive function. In men with genuine testosterone deficiency, Testogel aims to restore hormone levels to within the normal physiological range, thereby alleviating symptoms such as fatigue, reduced libido, erectile dysfunction, and loss of muscle strength.

Before prescribing Testogel, clinicians must confirm hypogonadism through at least two separate blood tests measuring total testosterone levels, typically taken in the morning when levels are naturally highest. Additional tests may include luteinising hormone (LH), follicle-stimulating hormone (FSH), and prolactin to determine the cause of low testosterone. According to British Society for Sexual Medicine guidance, testosterone replacement should only be initiated when there is both biochemical evidence of deficiency and associated clinical symptoms.

Important practical considerations include allowing the gel to dry completely before dressing (it is flammable until dry), washing hands thoroughly after application, and covering the application site with clothing to prevent transfer to others, particularly women and children. Patients should avoid bathing or swimming for several hours after application (2-6 hours depending on the product). It's also important to note that TRT suppresses sperm production and should be avoided by men wishing to father children.

Prostate Cancer Risk and Testosterone Replacement Therapy

The relationship between testosterone replacement therapy and prostate cancer remains one of the most scrutinised areas in men's health, and concerns about Testogel potentially causing prostate cancer are understandable but require careful contextualisation. Current evidence does not support a causal link between testosterone therapy and the development of prostate cancer in men without pre-existing disease. Multiple large-scale studies and systematic reviews have failed to demonstrate that TRT initiates prostate carcinogenesis in healthy prostatic tissue.

Historically, concerns arose from observations that prostate cancer cells are often androgen-sensitive, meaning they can grow more rapidly in the presence of testosterone. This led to the use of androgen deprivation therapy as a treatment for advanced prostate cancer. However, having normal testosterone levels does not appear to cause prostate cancer to develop. The MHRA product information for testosterone preparations acknowledges that whilst testosterone may stimulate growth of pre-existing prostate cancer, there is no conclusive evidence that it causes cancer in men with healthy prostates.

Known or suspected prostate cancer remains a contraindication to testosterone therapy according to the Testogel Summary of Product Characteristics. Before initiating Testogel, clinicians should conduct a thorough assessment including digital rectal examination (DRE) and measurement of prostate-specific antigen (PSA) levels, particularly in men over 40 or those with risk factors. Men with abnormal DRE findings or PSA above the age-specific reference range should be referred urgently to urology under the NICE suspected cancer pathway (NG12). For men already on TRT, regular monitoring of PSA levels is essential—typically at 3, 6, and 12 months after starting treatment, then annually thereafter. A rapid rise in PSA or development of lower urinary tract symptoms warrants immediate urological assessment and consideration of treatment cessation.

Other Cancer Risks Associated with Testogel

Beyond prostate cancer, questions occasionally arise about whether Testogel might increase the risk of other malignancies. There is no consistent evidence to date linking testosterone replacement therapy to increased risk of other cancers in men. Pharmacovigilance data and observational studies have not identified clear signals suggesting that physiological testosterone replacement causes breast cancer, colorectal cancer, lung cancer, or haematological malignancies, though the evidence base remains limited.

One area requiring mention is male breast cancer, which, whilst rare (accounting for less than 1% of all breast cancers), is listed as a contraindication to testosterone therapy in the Testogel Summary of Product Characteristics. This precaution exists because breast tissue contains androgen receptors, and testosterone can be converted to oestradiol through aromatisation. However, there is no evidence that testosterone therapy in men without pre-existing breast pathology initiates breast cancer development. The contraindication applies to men with known or suspected breast carcinoma.

Polycythaemia (elevated red blood cell count) represents an important adverse effect of testosterone therapy that requires monitoring, as it can increase blood viscosity and theoretically raise cardiovascular risks. Testosterone stimulates erythropoiesis (red blood cell production) in the bone marrow. Whilst polycythaemia itself is not cancer, severe cases may require dose reduction or temporary cessation of treatment. Regular monitoring of haematocrit levels is recommended—typically at baseline, 3-4 months after initiation, then annually. Values consistently above 0.54 (54%) warrant dose adjustment or interruption of therapy.

The MHRA product information also highlights an increased risk of venous thromboembolism (VTE) in men with thrombophilia receiving testosterone therapy, requiring clinical vigilance. Some observational studies have suggested that correcting testosterone deficiency might be associated with reduced overall mortality risk in hypogonadal men, though this remains an area of ongoing research and causality has not been established. The key principle is that testosterone replacement should restore levels to within the normal physiological range, not exceed it, thereby minimising potential risks whilst addressing genuine deficiency.

Safety Monitoring and When to Seek Medical Advice

Appropriate safety monitoring is essential for all men receiving Testogel to ensure both efficacy and early detection of potential adverse effects. UK clinical guidance recommends a structured monitoring schedule that includes clinical assessment and specific blood tests at defined intervals.

Baseline investigations before starting Testogel should include:

• Two early-morning total testosterone measurements (to confirm hypogonadism)

• Luteinising hormone (LH) and follicle-stimulating hormone (FSH)

• Prolactin (to exclude pituitary causes)

• Full blood count (to assess haematocrit and haemoglobin)

• Prostate-specific antigen (PSA) in men over 40 or with risk factors

• Digital rectal examination in appropriate patients

• Liver function tests and lipid profile if clinically indicated

Follow-up monitoring typically occurs at 3 months, 6 months, 12 months, and then annually, assessing testosterone levels (to ensure adequate replacement), haematocrit (to detect polycythaemia), and PSA levels (in men over 40). Clinical review should evaluate symptom improvement, potential adverse effects, and adherence to treatment.

Patients should seek immediate medical advice if they experience:

• New or worsening lower urinary tract symptoms (hesitancy, poor stream, nocturia)

• Blood in urine or semen

• Persistent bone pain

• Unexplained weight loss or night sweats

• Breast lumps or nipple discharge

• Severe headaches or visual disturbances

• Signs of blood clots (leg swelling, chest pain, breathlessness)

Call 999 or attend A&E for severe chest pain, sudden breathlessness, or signs of pulmonary embolism.

Common adverse effects that should be reported to your GP include skin reactions at application sites, acne or oily skin, mood changes, ankle swelling, or breast tenderness. Patients should report any suspected side effects via the MHRA Yellow Card scheme. It is crucial to attend all scheduled monitoring appointments, as some adverse effects may be asymptomatic but require intervention.

Patients should be aware of potential drug interactions, including enhanced anticoagulant effects with warfarin, possible changes in insulin or oral antidiabetic requirements, and increased risk of fluid retention when used with corticosteroids. Never share Testogel with others, and ensure proper application technique to prevent transfer to family members, particularly women and children, in whom testosterone exposure can cause harmful virilisation effects.

Frequently Asked Questions