The role of DNA repair capacity in melanoma skin cancer risk in a population chronically exposed to high levels of sunlight

Abstract

Puerto Rican residents are exposed to some of the highest levels of environmental ultraviolet radiation in the world; paradoxically, the melanoma incidence in Puerto Rico is lower than that of the US mainland. The overall objective of this case-control pilot study was to test the hypotheses that (1) persons with melanoma have a significantly lower DNA repair capacity (DRC) in relation to controls matched by age, (2) decline in DRC is associated with vertical depth of melanoma invasion, and (3) DRC is associated with anatomical tumor location. Controls (n = 124) were examined by dermatologists; cases (n = 62) were histopathologically confirmed. The mean DRC ± 1 SE of controls was 6.46% ± 0.3. Melanoma patients (n = 62) had a mean decrease in DRC of 3% (6.25% ± 0.5), which was not statistically different from controls (P = 0.697). No significant differences in DRC were evident in participants with either in situ or malignant melanoma tumors; neither were such differences evident when evaluating anatomical location of tumors (ie, non-sun-exposed versus sun-exposed). DRC generally declined in participants with increased depth of melanoma tumor penetration when compared with controls and those with small in situ tumors. These findings should be examined in a larger-scale population study that includes participants with more advanced metastatic melanoma.

Keywords: Case-control study; DNA repair capacity; high UV exposure; melanoma; risk factors; skin cancer.

Figure 1

Age-adjusted percentage DNA repair capacity (DRC) of persons in Puerto Rico without skin cancer (n  =  124) and with melanoma skin cancer (n  =  62). DRC was measured in lymphocytes by using the host-cell reactivation assay with a luciferase reporter gene according to Matta et al. Values are expressed as the mean ± standard error of the mean. Patients with melanoma had a 3% reduction in DRC, as compared to controls, that was not statistically significant (P  =  .697, Student's t test).

Figure 2

DNA repair capacity (DRC) of controls in terms of their type (in situ and malignant melanoma). Values are expressed as the mean ± standard error of the mean and adjusted by age.

Figure 3

DNA repair capacity (DRC) of controls versus cases as a function of tumor depth, based on the Breslow index, with corresponding P value obtained through a Student's t test.

Figure 4

The association between DNA repair capacity (DRC) and the anatomical location of both in situ and malignant melanoma tumors in terms of sun exposure was analyzed. Patients with melanoma skin cancer in sun-exposed areas had a 38% reduction in DRC when compared to controls with borderline significance, P  =  0.055.