Sunburn More Likely to Cause Non-Malignant Skin Cancer

[Editor-in-Chief]

Sunburn More Likely to Cause Non-Malignant Skin Cancer

By Neil Osterweil, Senior Associate Editor, MedPage Today
Reviewed by Zalman S. Agus, MD; Emeritus Professor at the University of Pennsylvania School of Medicine.
December 21, 2005

MedPage Today Action Points

• Inform patients who ask that this study suggests that ultraviolet B-induced skin damage may put them more at risk for basal cell and squamous cell carcinomas than for malignant melanoma.
• Explain that these data come from laboratory studies of cells and need to be confirmed in prospective studies.
• Advise patients to continue avoiding excessive sun exposure, use sunscreens that block both ultraviolet-A and ultraviolet-B rays, and to wear appropriate hats and clothing when spending long periods of time out of doors.

Review
HOUSTON, Dec. 21 - The sun may not be quite the melanoma threat it's cracked up to be, according to researchers here.

Ultraviolet B-induced damage to skin cells is more likely to lead to non-malignant forms of skin cancer than to cutaneous malignant melanomas, suggested researchers on the basis of an in vitro study at the M.D. Anderson Cancer Center.

That doesn't mean that sunbathing is off the hook, Qingyi Wei, M.D., Ph.D., and colleagues reported in the Dec. 21 issue of the Journal of the National Cancer Institute.

Exposure to ultraviolet A (UVA) rays leads to premature aging of the skin and DNA damage in melanocytes, the Houston team said, and UVB is still partly associated with the development of melanoma, although the effect is weaker than it is with other, non-malignant forms of skin cancer,

The investigators conducted an in vitro study of the relationship between UVB exposure and chromosomal damage in skin cells from patients with basal- and squamous-cell carcinomas, malignant melanoma, and controls.

"Although we have refined the common wisdom that excess sun exposure is always associated with increased risk of skin cancer, the take-home message for the public is still the same -- limit sun exposure and use a sunscreen that blocks both UVA and UVB rays," Dr. Wei said.

He and colleagues collected white blood cells from 469 skin-cancer patients (238 of whom had melanoma) and 329 cancer-free controls. The cells were exposed in vitro to UVB radiation at a dose of 150 joules/m2, and 24 hours later were examined for mutagen sensitivity as measured by the number of UVB-induced chromatid breaks per cell.

They found that the mean number of UVB-induced chromatid breaks per cell was significantly higher among patients with non-malignant cancers compared with controls, but there was no difference in mutagen sensitivity between patients with melanoma and controls.

Specifically, controls had a mean of 0.28 breaks per cell (95% confidence interval, 0.27 to 0.30), patients with basal cell carcinoma had 0.36 breaks per cell (95% CI, 0.33 to 0.39 P=0.001), patients with squamous cell cancers had 0.35 breaks per cell, (95% CI, 0.32 to 0.38, P<0.001), and patients with malignant melanoma had a mean of 0.30 breaks per cells (95% CI, 0.28 to 0.33, P = o.22).

Patients whose cells had more chromatid breaks than those found in the median of control subjects had a nearly threefold increased risk for both basal and squamous cell cancers, but not for malignant melanoma.

The authors also found that there was a dose-response relationship between mutagen sensitivity and risk for both basal cell and squamous cell carcinomas (P for trend <0.001 for both cancers relative to controls).

Looking at interactions between mutagen sensitivity and various known risk factors for skin cancer and their possible relationship to the various types of cancer, they found that in particular a history of blistering sunburns was significantly associated with basal cell carcinoma, and that hair color, tanning ability and family history of skin cancer was associated with squamous cell carcinoma. In contrast, there were similar interactions between mutagen sensitivity, risk factors, and melanoma.

"These findings suggest that in vitro UVB-induced mutagen sensitivity reflects susceptibility to non-malignant skin cancer, but not cutaneous malignant melanoma," the author noted. They acknowledged, however, that the case-control design of the study may introduce unintended bias, and that prospective studies are needed to validate their findings. In this hospital case -- control design, the control participants were visitors to the hospital rather than patients, and they may not come from the same residential areas as the case patients.

Primary source: Journal of the National Cancer Institute.
Source reference:
Wang LE et al. In Vitro Sensitivity to Ultraviolet B Light and Skin Cancer Risk: A Case - Control Analysis. Natl Cancer Inst 2005;97:1822 - 31

Source