One of the most prescribed high blood pressure drugs in Australia increases older people’s risk of developing skin cancer, according to a University of NSW study.
But researchers warn that it may still be dangerous to suddenly stop taking the medicine.
Hydrochlorothiazide contains photosynthesising properties, which can make your skin more sensitive to the sun, the scientists say.
The findings are based on analysis of skin cancer rates in a case-control study involving older Australians. The results, published in Basic & Clinical Pharmacology & Toxicology, support similar findings from previous international studies.
“We found increased risk for developing malignant melanoma and squamous cell cancer of the lip (lip cancer) with hydrochlorothiazide use,” says pharmacoepidemiologist Dr Benjamin Daniels, lead author of the study and research fellow at UNSW Medicine’s Centre for Big Data Research in Health (CBDRH). Dr Daniels studies the use and effects of drugs in specific population groups.
“For lip cancer, the risk also appears to be cumulative – that is, the longer that hydrochlorothiazide is used, the higher the risk of developing lip cancer,” he says.
High blood pressure – or hypertension – is a chronic illness affecting more than a third of Australians over the age of 18. It is usually defined by blood pressure levels above 140/90. If left untreated, hypertension can lead to serious health conditions including stroke and heart disease.
Sufferers are generally prescribed medicine, such as hydrochlorothiazide, and urged to make healthy lifestyle changes to their diet and exercise regimes.
“Hypertension is a condition that needs to be carefully managed,” says Dr Daniels.
“We don’t want anyone to suddenly stop taking hydrochlorothiazide out of fear of developing skin cancer.
“The skin cancer risk is something for prescribers to be aware of. Doctors may want to consider conducting more skin checks for their patients or reinforcing advice around sun-smart behaviours that everyone should be aware of, like adequate protection when UV is higher than three and avoiding sun exposure during peak UV times.”
He says the study has resulted in an update to the product information.
A spokesperson from the Therapeutic Goods Administration (TGA) said: “This [update] will help prescribers and patients make informed choices about the benefits and risks of hydrochlorothiazide-containing medicines.”
The TGA encourages anyone with concerns to speak with their healthcare professional.
Australia has one of the highest rates of skin cancer in the world, according to the Cancer Council, which reports that about two in three Australians will be diagnosed with a skin cancer by the time they are 70.
In other melanoma research, Centenary Institute scientists have discovered that genes on the X chromosome may be key to improved survival rates of females with melanoma – as compared to their male counterparts.
Dr Abdullah Al Emran, researcher in the Melanoma Oncology and Immunology Program at the Centenary Institute and lead author of the study, says: “We know that survival from melanoma is strongly related to gender, with females having a survival rate almost twice that of males.
“Many explanations such as behavioural differences in sun exposure and other factors have been previously proposed for this gender difference, but none had withstood critical scrutiny.”
The researchers explored a number of genes on the X chromosome and, more specifically, those genes that had been found to escape a cellular process called ‘X-inactivation’.
A normal regulatory process in the body, X-inactivation is where one of a female’s two X chromosomes is inactivated or silenced during embryonic development. Only one functional copy of the X chromosome is required in each body cell.
However, this ‘silencing’ process is not perfect, says Dr Emran, with between 10 and 20 per cent of the genes on the silenced X chromosome still able to be expressed. As a result, females have a double expression of many genes involved in immune responses when compared to males.
“Our study found that two of these genes on the X chromosome that manage to escape inactivation – the genes KDM6A and ATRX – were both associated with improved survival rates for women with melanoma. We believe that their high expression levels aid the body’s immune system in helping to fight cancer,” says Dr Emran.
Professor Peter Hersey, head of the Melanoma Oncology and Immunology Program at the Centenary Institute, believes the research findings are significant in pointing to KDM6A as a major regulator of immune responses. The focus will now be on how KDM6A is regulated, he says.
Do you take the blood pressure drug Hydrochlorothiazide? Were you aware that it increased the risk of skin cancer?
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