Squamous cell and basal cell carcinoma of the skin in relation to radiation therapy and potential modification of risk by sun exposure.
BACKGROUND
Epidemiologic studies consistently find enhanced risk of basal cell carcinoma of the skin among individuals exposed to ionizing radiation, but it is unclear whether the radiation effect occurs for squamous cell carcinoma. It is also not known whether subgroups of individuals are at greater risk, eg, those with radiation sensitivity or high ultraviolet radiation exposure.


METHODS
We analyzed data from a case-control study of keratinocyte cancers in New Hampshire. Incident cases diagnosed in 1993-1995 and 1997-2000 were identified through a state-wide skin cancer surveillance system, and controls were identified through the Department of Transportation and Center for Medicare and Medicaid Service Files (n = 1121 basal cell carcinoma cases, 854 squamous cell carcinoma cases, and 1049 controls).


RESULTS
We found an association between history of radiation treatment and basal cell carcinoma. The association was especially strong for basal cell carcinomas arising within the radiation treatment field (odds ratio = 2.6; 95% confidence interval = 1.5-4.3), and among those treated with radiation therapy before age 20 (3.4; 1.8-6.4), those whose basal cell carcinomas occurred 40 or more years after radiation treatment (3.2; 1.8-5.8), and those treated with radiation for acne (11; 2.7-49). Similar age and time patterns of risk were observed for squamous cell carcinoma, although generally with smaller odds ratios. For basal cell carcinoma, early exposure to radiation treatment was a risk factor largely among those without a history of severe sunburns, whereas for squamous cell carcinoma, radiation treatment was a risk factor primarily among those with a sun-sensitive skin type (ie, a tendency to sunburn).


CONCLUSIONS
Radiation treatment, particularly if experienced before age 20, seems to increase the long-term risk of both basal and squamous cell carcinomas of the skin. These risks may differ by sun exposure or host response to sunlight exposure.
Karagas
Margaret R
MR
Section of Biostatistics and Epidemiology, Department of Community and Family Medicine, and the Norris Cotton Cancer Center, Dartmouth Medical School, Lebanon, NH 03756, USA. margaret.karagas@dartmouth.edu
Nelson
Heather H
HH
Zens
Michael S
MS
Linet
Martha
M
Stukel
Therese A
TA
Spencer
Steve
S
Applebaum
Katie M
KM
Mott
Leila
L
Mabuchi
Kiyohiko
K
D000328:Adult; D000368:Aged; D002294:Carcinoma, Squamous Cell / Q000453:epidemiology* / Q000209:etiology; D004781:Environmental Exposure; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018295:Neoplasms, Basal Cell / Q000453:epidemiology* / Q000209:etiology; D009513:New Hampshire / Q000453:epidemiology; D011159:Population Surveillance; D011839:Radiation, Ionizing; D011859:Radiography / Q000009:adverse effects*; D018570:Risk Assessment; D012878:Skin Neoplasms / Q000453:epidemiology / Q000209:etiology*