Basal cell carcinoma: from host response and polymorphic variants to tumour suppressor genes

Photodynamic Therapy for Basal Cell Carcinoma: The Clinical Context for Future Research Priorities

Photodynamic therapy (PDT) is an established treatment option for low-risk basal cell carcinoma (BCC). BCC is the most common human cancer and also a convenient cancer in which to study PDT treatment. This review clarifies challenges to researchers evident from the clinical use of PDT in BCC treatment. It outlines the context of PDT and how PDT treatments for BCC have been developed hitherto. The sections examine the development of systemic and subsequently topical photosensitizers, light delivery regimens, and the use of PDT in different patient populations and subtypes of BCC. The outcomes of topical PDT are discussed in comparison with alternative treatments, and topical PDT applications in combination and adjuvant therapy are considered. The intention is to summarize the clinical relevance and expose areas of research need in the BCC context, ultimately to facilitate improvements in PDT treatment.

Association between genetic variation within vitamin D receptor-DNA binding sites and risk of basal cell carcinoma

An increasing number of studies have reported a protective association between vitamin D and cancer risk. The vitamin D endocrine system regulates transcriptional programs involved in inflammation, cell growth and differentiation through the binding of vitamin D receptor (VDR) to specific VDR elements. However, limited attention has been given to the role of variation within VDR binding sites in the development of basal cell carcinoma (BCC). Across 2,776 previously identified VDR binding sites, we identified 2,540 independent single-nucleotide polymorphisms (SNPs) and examined their associations with BCC risk in a genome-wide association meta-analysis totaling 17,187 BCC cases and 287,054 controls from two data sets. After multiple testing corrections, we identified two SNPs at new loci (rs16917546 at 10q21.1: odds ratio (OR) = 1.06, p = 3.16 × 10^-7 and rs79824801 at 12q13.3: OR = 1.10, p = 1.88 × 10^-5 ) for the first time as independently related to BCC risk in meta-analysis; and both SNPs were nominally significant in two data sets. In addition, the SNP rs3769823 within VDR binding site at a previously reported BCC susceptibility locus (2q33.1, rs13014235) also exhibited a significant association (OR = 1.12, p = 3.99 × 10^-18 ). A mutually adjusted model suggested that rs3769823 explained the signal in this region. Our findings support the hypothesis that inherited common variation in VDR binding sites affects the development of BCC.

Basal Cell Carcinoma: Review of Epidemiology, Pathogenesis, and Associated Risk Factors

Background:

Basal cell carcinoma (BCC) is extremely common, and its incidence continues to rise.

Objective:

This review presents the literature pertaining to the epidemiology, pathogenesis, and risk factors associated with BCC.

Conclusions:

The risk of developing BCC depends on both genetic predisposition and exposure to risk. Fair-skinned people account for the overwhelming majority of patients, beyond what would be expected by skin phototype alone. Damage to multiple lines of defense appears to be necessary for cancer development and spread. This damage distorts the concerted effort of deoxyribonucleic acid (DNA) repair, immunosurveillance, and cellular growth regulation to protect against malignant progression. Ultraviolet light exposure is the most critical modifiable factor determining early expression and frequency of BCC development.

Integrating pathway analysis and genetics of gene expression for genome-wide association study of basal cell carcinoma

Genome-wide association studies (GWASs) have primarily focused on marginal effects for individual markers and have incorporated external functional information only after identifying robust statistical associations. We applied a new approach combining the genetics of gene expression and functional classification of genes to the GWAS of basal cell carcinoma (BCC) to identify potential biological pathways associated with BCC. We first identified 322,324 expression-associated single-nucleotide polymorphisms (eSNPs) from two existing GWASs of global gene expression in lymphoblastoid cell lines (n = 955), and evaluated the association of these functionally annotated SNPs with BCC among 2,045 BCC cases and 6,013 controls in Caucasians. We then grouped them into 99 KEGG pathways for pathway analysis and identified two pathways associated with BCC with p value <0.05 and false discovery rate (FDR) <0.5: the autoimmune thyroid disease pathway (mainly HLA class I and II antigens, p < 0.001, FDR = 0.24) and Janus kinase-signal transducer and activator of transcription (JAK-STAT) signaling pathway (p = 0.02, FDR = 0.49). Seventy-nine (25.7%) out of 307 significant eSNPs in the JAK-STAT pathway were associated with BCC risk (p < 0.05) in an independent replication set of 278 BCC cases and 1,262 controls. In addition, the association of JAK-STAT signaling pathway was marginally validated using 16,691 eSNPs identified from 110 normal skin samples (p = 0.08). Based on the evidence of biological functions of the JAK-STAT pathway on oncogenesis, it is plausible that this pathway is involved in BCC pathogenesis.

Genome-wide association study of skin complex diseases

Complex diseases are caused by both genetic and environmental factors. Over decades, scientists endeavored to uncover the genetic myth of complex diseases by linkage and association studies. Since 2005, the genome-wide association study (GWAS) has been proved to be the most powerful and efficient study design thus far in identifying genetic variants that are associated with complex diseases. More than 230 complex diseases and traits have been investigated by this approach. In dermatology, 10 skin complex diseases have been investigated, a wealth of common susceptibility variants conferring risk for skin complex diseases have been discovered. These findings point to genes and/or loci involved in biological systems worth further investigating by using other methodologies. Certainly, as our understanding of the genetic etiology of skin complex diseases continues to mature, important opportunities will emerge for developing more effective diagnostic and clinical management tools for these diseases.

Interaction between functional polymorphic variants in cytokine genes, established risk factors and susceptibility to basal cell carcinoma of skin

Basal cell carcinoma (BCC) of the skin is the most common neoplasm among the Caucasian population of the Western world. Inflammation may result in oxidative stress and contribute to promotion and progression of tumors, including BCC. The role of cytokines, which are inflammatory modulators, in the biology of tumors has been extensively studied and it is well known that they are aberrantly produced by cancer cells, macrophages and other phagocytic cells. Genetic polymorphisms are known in several cytokine genes, which result in altered expression. In the present association study, we investigated the association of 14 functional polymorphisms in 11 cytokines genes with BCC risk in 529 BCC cases and 532 healthy controls. We have also tested the possible interactions between the genetic variants and three known risk factors for BCC: skin complexion, sun effect and skin response to sun exposure. We did not observe any statistically significant association between SNPs and BCC risk. However, we found that, in a subgroup of subjects more prone to skin burns, carriers of at least one copy of the G allele of rs1800629 (TNF) had an increased risk of BCC [odds ratio (OR) = 2.40, 95% confidence interval (CI) 1.38-4.16, P = 0.0005]. Moreover, in subjects less prone to sunburns, we observed that carriers of the C allele of rs1143627 (IL1B) showed a decreased risk (OR = 0.53, 95% CI 0.34-0.82, P = 0.0019). In conclusion, we found that two polymorphisms in inflammatory genes interacting with environmental risk factors could modulate BCC risk.

Non-melanoma skin cancer

The rising incidence and morbidity of non-melanoma skin cancers has generated great interest in unravelling of their pathogenesis and in the search for new non-invasive treatments. Whereas the role of cumulative sun exposure in pathogenesis of squamous-cell carcinoma seems clear, the relation between sun-exposure patterns and subtypes of basal-cell carcinoma remains undetermined. Several complex genotypic, phenotypic, and environmental factors contribute to pathogenesis of non-melanoma skin cancers. Unlike basal-cell carcinoma, squamous-cell carcinomas can arise from precursor lesions. Diagnosis of non-melanoma skin cancer is made clinically and confirmed by histological testing. Prognosis depends on lesion and host characteristics, which also dictate choice of treatment. Prevention strategies aim at reduction of sun exposure, but are of unproven benefit, especially for basal-cell carcinoma. Surgical excision with predetermined margins is the mainstay of treatment for squamous-cell carcinoma and for most basal-cell carcinomas. Of the new non-invasive treatments, only photodynamic therapy and topical imiquimod have become established treatments for specific subtypes of basal-cell carcinoma, and the search for more effective and tissue-salvaging therapies continues.

Common variants on 1p36 and 1q42 are associated with cutaneous basal cell carcinoma but not with melanoma or pigmentation traits

To search for new sequence variants that confer risk of cutaneous basal cell carcinoma (BCC), we conducted a genome-wide SNP association study of 930 Icelanders with BCC and 33,117 controls. After analyzing 304,083 SNPs, we observed signals from loci at 1p36 and 1q42, and replicated these associations in additional sample sets from Iceland and Eastern Europe. Overall, the most significant signals were from rs7538876 on 1p36 (OR = 1.28, P = 4.4 x 10(-12)) and rs801114 on 1q42 (OR = 1.28, P = 5.9 x 10(-12)). The 1p36 locus contains the candidate genes PADI4, PADI6, RCC2 and ARHGEF10L, and the gene nearest to the 1q42 locus is the ras-homolog RHOU. Neither locus was associated with fair pigmentation traits that are known risk factors for BCC, and no risk was observed for melanoma. Approximately 1.6% of individuals of European ancestry are homozygous for both variants, and their estimated risk of BCC is 2.68 times that of noncarriers.

Case-control study in basal cell carcinoma of the skin: single nucleotide polymorphisms in three interleukin promoters pre-analysed in pooled DNA

BACKGROUND

Basal cell carcinoma (BCC) is one of the most common neoplasms in the world. Development of BCC is associated with environmental factors (especially sun exposure) as well as heritable factors.

OBJECTIVES

To analyse three single nucleotide polymorphisms (SNPs) in the promoter regions of interleukin (IL) genes in genomic DNA from 527 cases of BCC and 530 matched controls and to examine if DNA pooling is a useful method on which to base decisions regarding further SNP analysis.

METHODS

The SNPs analysed were IL6-597, IL10-1082 and IL1B-511. The SNPs were first analysed from pooled DNA and afterwards from individual samples. The DNA pools resulted from a division of the samples into cases and controls, female and male, and three age groups. In these pools the allele frequencies were estimated by two methods, real-time polymerase chain reaction with allele-specific primers, and quantitative sequencing.

RESULTS

No significant association was found when the allele frequencies in cases and controls were compared. However, by analysis of the individual genotypes we found SNP IL6-597 G/A to be significantly associated with BCC risk (P =0.007). Hereby the heterozygous genotype 'GA' had a protective effect (odds ratio 0.64, 95% confidence interval 0.49-0.84). No significant association was found for IL10-1082 and IL1B-511.

CONCLUSIONS

The association of SNP IL6-597 with BCC could be found only by individual genotyping, but would have been missed if only data from the pooling analysis had been known.

Towards a more specific therapy: targeting nonmelanoma skin cancer cells

Epithelial cancers of the skin, e.g. basal cell carcinoma and squamous cell carcinoma, are the most common tumours in humans with increasing incidence. Hence the development of new therapeutic strategies is of utmost interest. For many years the most often used conventional therapies for these diseases were surgical procedures such as curettage and electrodesiccation, excision or, with so far the best outcome in terms of remission rates, micrographic surgery. Other ablative treatment modalities are cryotherapy, radiation therapy or the use of lasers (Er:YAG, CO(2)). All those above-mentioned treatments have in common that they are quite unspecific and do not target the tumour itself or its environment, thus leading to unwanted effects in the surrounding tissue such as scar formation or other cosmetically disfiguring events. Therefore, the development of novel, more pathogenesis-based therapies such as the use of retinoids, cyclooxygenase inhibitors, topical immunomodulators, inhibitors of the sonic-hedgehog signalling pathway or photodynamic therapy are challenging new approaches.