WHO Cancer Agency IARC Classifies Hydrochlorothiazide, Voriconazole, Tacrolimus as Human Carcinogens
Hyderabad: The International Agency for Research on Cancer (IARC), the specialized cancer research arm of the World Health Organization (WHO), has classified three widely used active pharmaceutical ingredients, Hydrochlorothiazide (HCTZ), Voriconazole, and Tacrolimus, as Group 1 carcinogens, indicating there is conclusive scientific evidence that these agents can cause cancer in humans.
However, health experts have strongly advised patients to continue their prescribed treatment and consult their doctors before making any changes, warning that uncontrolled hypertension poses a far greater immediate health risk.
Hydrochlorothiazide is a commonly prescribed medicine for the treatment of essential hypertension and edema, while Voriconazole is a broad-spectrum triazole antifungal used for severe systemic fungal infections. Tacrolimus is an immunosuppressive medicine administered to prevent organ rejection in transplant recipients and is also used topically for skin conditions such as eczema and vitiligo.
According to the WHO, the findings have been published in Volume 137 of the IARC Monographs following an extensive review of epidemiological studies, animal bioassays, and mechanistic evidence by an international working group of experts.
The WHO stated that Hydrochlorothiazide, which had previously been classified as possibly carcinogenic (Group 2B), has now been upgraded to Group 1 based on strong epidemiological evidence linking prolonged use to an increased risk of non-melanoma skin cancers, particularly squamous cell carcinoma (SCC) of the skin and lip cancer. The agency noted that the drug is phototoxic, and exposure to ultraviolet (UV) radiation from sunlight can trigger cellular oxidative stress in the skin.
Regarding Voriconazole, the WHO explained that the medicine, widely used in post-transplant care and intensive care settings, breaks down into a primary metabolite known as N-oxide, which exhibits significant phototoxicity and contributes to skin cell damage following exposure to ambient sunlight.
The WHO also stated that Tacrolimus, generally administered orally or intravenously to transplant recipients, suppresses immune surveillance, reducing the body's ability to eliminate abnormal cell proliferation. This mechanism increases the long-term risk of Non-Hodgkin lymphoma and skin malignancies.
Despite the classification, the WHO has advised patients not to discontinue their prescribed medicines abruptly, particularly those taking Hydrochlorothiazide for blood pressure control, without consulting a general physician or hypertension specialist. The agency stressed that any change in treatment should be made only under medical supervision.
The report noted that the WHO classification could have implications for clinical practice in Telangana, where nearly 27 lakh people are living with hypertension. According to doctors in Hyderabad, Hydrochlorothiazide is now rarely prescribed as a standalone medicine and is more commonly used in low-cost fixed-dose combination therapies alongside angiotensin receptor blockers (ARBs) such as Telmisartan, Losartan, and Olmesartan.
Health authorities and cardiologists have emphasized that the immediate dangers of uncontrolled hypertension, including stroke, heart attack, and kidney failure, outweigh the long-term statistical risk of skin cancer associated with Hydrochlorothiazide. They also pointed out that several alternative antihypertensive treatment regimens are available for patients if clinically required, reports Telangana Today.
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