Absence of Basal Cell Carcinoma in Irradiated Childhood Cancer Survivors of Black Race: A Report from the St. Jude Lifetime Cohort Study

Abstract

Background: Cancer survivors exposed to therapeutic radiation are at increased risk for basal cell carcinoma (BCC). Despite the notable influence of race on rates of BCC in the general population, the same is not clearly defined in previously irradiated cancer survivors. We investigated the influence of race on the development of BCC in adult survivors of childhood cancer.

Methods: Using a retrospective cohort study, outcomes were collected through June 30, 2015, for 1,746 irradiated childhood cancer survivors participating in the St. Jude Lifetime Cohort Study (SJLIFE), comprising a total of 33,147 person-years of follow-up. Subsequent neoplasms identified in survivors through self-report and prospective clinical assessment were validated by pathology reports. Expected numbers of each type of radiation-associated neoplasm, including BCC, were calculated for irradiated black survivors based on rates in irradiated white survivors, accounting for primary cancer diagnosis, diagnosis year, attained age, and sex.

Results: On the basis of the rate of BCC in previously irradiated white survivors, 56.1 BCCs were expected among 237 black survivors, yet none observed. In contrast, the observed-to-expected ratio of non-BCC radiation-associated neoplasms (melanoma, brain, breast, thyroid cancer) was 0.88 (30 observed/34.2 expected, 95% confidence interval, 0.59-1.25).

Conclusions: We identified an unexpected absence of BCC in irradiated black survivors in SJLIFE. We observe a similar absence of BCC in black individuals among two additional cohorts treated with irradiation for childhood cancer.

Impact: Black survivors are at a substantially reduced or absent risk for BCC from therapeutic radiation for reasons not yet fully understood. Cancer Epidemiol Biomarkers Prev; 25(9); 1356-60. ©2016 AACR.

Figure 1

Effect of ionizing radiation on the development of basal cell carcinoma (BCC) in childhood cancer survivors. * High exposure of short duration ** Rates for general population from Asgari, et al.