WHO cancer agency flags 3 widely used medicines as carcinogenic to humans

The World Health Organisation (WHO) cancer agency has placed hydrochlorothiazide, voriconazole and tacrolimus in its Group 1 carcinogen category. The finding identifies a cancer hazard but does not mean patients should stop treatment without medical advice.

In Short

• Review drew on epidemiological studies, animal experiments and mechanistic evidence
• Hydrochlorothiazide is tied to skin and lip cancers through photosensitivity
• Voriconazole's phototoxic effects may help explain linked squamous cell skin cancer

The World Health Organization’s (WHO) cancer research arm, the International Agency for Research on Cancer (IARC), has classified three widely used medicines – hydrochlorothiazide, voriconazole, and tacrolimus – as Group 1 carcinogens, the category reserved for agents considered “carcinogenic to humans”.

The latest decision follows a review of epidemiological studies, animal experiments and mechanistic evidence, and is detailed in IARC Monographs Volume 137.

The classification, however, is not a recommendation to stop taking these medicines. IARC identifies whether an agent can cause cancer under certain circumstances (hazard identification); it does not assess the level of risk for an individual patient or weigh the benefits of treatment against potential harms.

For many patients, these medicines remain life-saving and essential when used under medical supervision.

WHAT THE DRUGS DO

Hydrochlorothiazide is one of the world's most commonly prescribed thiazide diuretics for treating high blood pressure and fluid retention. IARC concluded there is sufficient evidence that it causes squamous cell carcinoma of the skin and cancer of the lip, with additional but more limited evidence for some other skin cancers.

The drug is known to increase sensitivity to ultraviolet (UV) radiation, which is believed to contribute to the risk.

In India, hydrochlorothiazide is sold under brands such as Aquazide (Sun Pharma) and Hydrazide (Cipla). It is also widely available in fixed-dose combinations with blood pressure medicines, including Telma H and Telmikind-H.

Voriconazole, on the other hand, is a broad-spectrum antifungal medicine used to treat severe fungal infections such as invasive aspergillosis, particularly in patients with weakened immune systems or organ transplants.

IARC found sufficient evidence linking the drug to squamous cell carcinoma of the skin, with evidence suggesting that its phototoxic effects may play an important role.

Popular Indian brands include VFend (Pfizer), Voritek (Cipla) and Vorizol (Natco Pharma).

Tacrolimus is an immunosuppressant used primarily to prevent organ rejection after kidney, liver or heart transplantation. It is also used to prevent graft-versus-host disease after stem-cell transplantation, while topical formulations are prescribed as second-line treatment for atopic dermatitis and vitiligo.

IARC concluded there is sufficient evidence that tacrolimus causes non-Hodgkin lymphoma and post-transplant lymphoproliferative disorder, with limited evidence for leukaemia and squamous cell skin cancer.

Popular Indian brandsfor this drug include Pangraf (Mankind Pharma), Tacrograf and Tbis (Eris Lifesciences), Takfa (Intas Pharmaceuticals), Tacrotor (Torrent Pharma), and topical formulations such as Tacroz (Glenmark) and Talimus (Ajanta Pharma).

WHAT IT MEANS

Experts stress that the findings should not trigger panic. All three medicines are included in the WHO Model List of Essential Medicines because of their proven therapeutic value.

The new classification is intended to help clinicians and regulators better understand long-term cancer hazards, improve patient counselling and reinforce measures such as UV protection and regular monitoring where appropriate.

Patients are advised not to discontinue treatment without consulting their doctor, as the risks of untreated hypertension, invasive fungal infections or organ rejection can far outweigh the potential long-term cancer risk in many clinical situations.

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