The findings of a new study suggest there may be a skin cancer risk associated with hydrochlorothiazide (HCTZ) and other thiazide-based drugs used for treatment of blood pressure.
In a report published this month in the Canadian Medical Association Journal (CMAJ), researchers with the University of Toronto sought to assess a long-held belief that there was some connection between thiazides, a class of antihypertensive medications, and an increased risk of skin cancer.
While the link has previously been unclear, the new findings appear to affirm those suspicions, finding a more than 30% increased risk of melanoma skin cancer among users of the blood pressure drugs.
Researchers note the association has been indicated in previous studies, so this time they conducted a cohort study involving nearly a million adults ages 66 or older over a period of about 20 years. The study matched 302,634 adults prescribed an antihypertensive medication to 605,268 unexposed adults from 1998 to 2017.
The medications included thiazides, like HCTZ, as well as angiotensin-converting enzyme inhibitors, angiotensin II receptor blockers, calcium channel blockers and beta blockers. Researchers looked at the cumulative dose with each class and looked for diagnoses of keratinocyte carcinoma, advanced keratinocyte carcinoma and melanoma.
According to the findings, higher levels of thiazide exposure led to a slight increase in the risk of keratinocyte carcinoma; an increase of about eight percent. Advanced keratinocyte increased by a similar amount. However, the risk of melanoma, an often-deadly form of skin cancer, increased by 34%. No other blood pressure medications were associated with an increase in skin cancer, the researchers reported.
The researchers said that while ultraviolet (UV) radiation exposure was still the most important environmental risk factor associated with skin cancer, medication-induced phototoxicity, where a drug interacts with UV radiation to cause cellular skin damage, was something health care professionals and researchers should be concerned about.
“Higher cumulative exposure to thiazides was associated with increased rates of incident skin cancer in people aged 66 years and older,” the researchers determined. “Consideration of other antihypertensive treatments in patients at high risk of skin cancer may be warranted.”
The researchers noted that while many hypertension drugs are reported to be phototoxic, HCTZ is considered to be the most phototoxic of all blood pressure medications, and is often the first go-to medication for doctors treating patients for high blood pressure.