No Association between Telomere Length in Peripheral Blood Leukocytes and the Risk of Nonmelanoma Skin Cancer

Telomeres are long hexameric (TTAGGG)n repetitive structures capping the ends of eukaryotic chromosomes that protect against fusion and degradation of chromosomal ends and help maintain structural integrity. Recent reports have suggested that telomere length plays an important role in cancer development (1–3). In our previous study, we found that the telomere length in peripheral blood leukocytes may be associated with risk of skin cancer (4), the most common malignancy in the United States. To confirm and extend our observations, we prospectively evaluated the association between the telomere length and risk of skin squamous cell carcinoma (SCC) and basal cell carcinoma (BCC) within the Nurses' Health Study (NHS) and Health Professionals Follow-up Study (HPFS).

We conducted a nested case–control study within the HPFS, which was initiated in 1986 among 51,529 U.S. male professionals, aged 40 to 75 years at study entry. Between 1993 and 1994, 18,159 study participants provided blood samples. Eligible cases consisted of men with pathologically confirmed incident SCC from the subcohort who gave a blood sample, with a diagnosis after blood collection up to 2006. Participants who had cancer previously were excluded. For each case, 1 control was matched by age (±1 year) and was free of cancer up to and including the questionnaire cycle in which the case was diagnosed. In total, there are 241 Caucasian SCC cases and 241 matched Caucasian controls.

The NHS was established in 1976 among 121,700 female registered nurses between the ages of 30 and 55. Between 1989 and 1990, blood samples were collected from 32,826 of the cohort members. We have accrued 2,857 incident cases of BCC from the subcohort who had given a blood specimen, with a diagnosis between 1998 and 2008. We randomly selected a subset of BCC cases. Participants who had previously diagnosed cancer were excluded. One control was matched to each case by age (±1 year) and was free of cancer up to and including the questionnaire cycle in which the case was diagnosed. The nested case–control study consisted of 260 Caucasian BCC cases and 260 matched Caucasian controls.

In addition, we had telomere length measurements in several nested case–control studies within the NHS, including stroke, myocardial infarction, and endometrial cancer. We used all the controls from these studies. All cases were women diagnosed with BCC after blood collection and up to 2008 without personal history of other cancer. Controls were restricted to participants without a personal history of any cancer. We identified 363 Caucasian cases and 1,683 Caucasian controls.

Information regarding skin cancer risk factors was obtained from the prospective biennial questionnaires. The study was approved by the Brigham and Women's Hospital Institutional Review Board for Human Subjects Research.

Genomic DNA was extracted from peripheral leukocytes using the QIAmp 96-spin blood protocol. The relative average telomere length was determined by a high-throughput 384-well real-time PCR assay with an Applied Biosystems 7900HT PCR System. The T/S ratio (−dC_t) for each sample was calculated by subtracting the average 36B4 C_t value from the average telomere C_t value. The relative T/S ratio (−ddC_t) was determined by subtracting the T/S ratio value of the 5 ng standard curve point from the T/S ratio of each unknown sample. The blind quality–control samples were interspersed throughout the sets for assessing inter- and intraplate variability. The coefficients of variation (CV) of the telomere C_t and 36B4 C_t were 2.97% and 1.76%, respectively.

In the HPFS nested case–control study of SCC and the first NHS nested case–control study of BCC, relative telomere length was categorized into quartiles according to the distribution in each study-specific control population. OR and 95%CI were calculated to examine the relationship between relative telomere length and skin cancer by conditional logistic regression. In the second NHS nested case–control study of BCC, we calculated a z score in each set and pooled the z scores for further analysis. The z scores were categorized into quartiles according to the distribution among BCC controls. Unconditional logistic regression was employed to calculate OR and 95%CI. All statistical tests were 2 sided.

The characteristics of cases and controls in the SCC and BCC case–control study are presented in Table 1. Cases were more likely to have light pigmentary phenotypes, including lighter hair color and less tendency to tan. The association between relative telomere length and each type of skin cancer was examined separately (Table 2). No significant association was observed between telomere length and risk of SCC (P = 0.81). Similar null findings were observed between telomere length and risk of BCC in both studies (P = 0.83 and 0.39).

Recent studies have shown that telomere length is a potential biomarker of risk of various cancers, including bladder, breast, lung, stomach, head, and neck cancers (1–3, 5, 6). However, other epidemiologic investigations suggest that the associations between telomere length and cancer risk are inconclusive (7, 8). The heterogeneity across different tumors could likely be explained by the different telomere dynamics in different types of tissue. Telomere shortening and malignant transformation in different types of cells varies in response to environmental DNA damage exposure.

We previously observed that shorter telomere length was associated with a decreased risk of skin melanoma (4), and this finding was replicated in additional studies (manuscript in submission). Our previous data revealed no association between telomere length and skin SCC risk (P = 0.30; ref 4). Consistently, we found no associations between the telomere length and risk of SCC in the present study. We previously observed that shorter telomere length was nonsignificantly associated with an increased risk of BCC (P = 0.09; ref 4). In the present study of 2 prospective data sets, our results suggest that telomere length is not associated with BCC risk. The combined evidence indicates that the role of telomere length in BCC development is minimal.

In conclusion, the present prospective study found no association between relative telomere length in peripheral blood leukocytes and risk of nonmelanoma skin cancer. It suggests that telomere length may not be a useful biomarker for nonmelanoma skin cancer risk assessment.

No potential conflicts of interest were disclosed.

The authors thank Patrice Soule for preparing the DNA samples and Robert Farquhar for performing the telomere assays. They also thank the participants in the Nurses' Health Study and the Health Professionals Follow-Up Study for their dedication and commitment; the following state cancer registries for their help: AL, AZ, AR, CA, CO, CT, DE, FL, GA, ID, IL, IN, IA, KY, LA, ME, MD, MA, MI, NE, NH, NJ, NY, NC, ND, OH, OK, OR, PA, RI, SC, TN, TX, VA, WA, WY

This work is supported by NIH grants CA133914, CA87969, CA055075, and CA49449.