Occupational socioeconomic risk associations for head and neck cancer in Europe and South America: individual participant data analysis of pooled case-control studies within the INHANCE Consortium

BACKGROUND

The association between socioeconomic disadvantage (low education and/or income) and head and neck cancer is well established, with smoking and alcohol consumption explaining up to three-quarters of the risk. We aimed to investigate the nature of and explanations for head and neck cancer risk associated with occupational socioeconomic prestige (a perceptual measure of psychosocial status), occupational socioeconomic position and manual-work experience, and to assess the potential explanatory role of occupational exposures.

METHODS

Pooled analysis included 5818 patients with head and neck cancer (and 7326 control participants) from five studies in Europe and South America. Lifetime job histories were coded to: (1) occupational social prestige-Treiman's Standard International Occupational Prestige Scale (SIOPS); (2) occupational socioeconomic position-International Socio-Economic Index (ISEI); and (3) manual/non-manual jobs.

RESULTS

For the longest held job, adjusting for smoking, alcohol and nature of occupation, increased head and neck cancer risk estimates were observed for low SIOPS OR=1.88 (95% CI: 1.64 to 2.17), low ISEI OR=1.74 (95% CI: 1.51 to 1.99) and manual occupations OR=1.49 (95% CI: 1.35 to 1.64). Following mutual adjustment by socioeconomic exposures, risk associated with low SIOPS remained OR=1.59 (95% CI: 1.30 to 1.94).

CONCLUSIONS

These findings indicate that low occupational socioeconomic prestige, position and manual work are associated with head and neck cancer, and such risks are only partly explained by smoking, alcohol and occupational exposures. Perceptual occupational psychosocial status (SIOPS) appears to be the strongest socioeconomic factor, relative to socioeconomic position and manual/non-manual work.

DNA methylation changes associated with risk factors in tumors of the upper aerodigestive tract

Cancers of the upper aerodigestive tract (UADT) are common forms of malignancy associated with tobacco and alcohol exposures, although human papillomavirus and nutritional deficiency are also important risk factors. While somatically acquired DNA methylation changes have been associated with UADT cancers, what triggers these events and precise epigenetic targets are poorly understood. In this study, we applied quantitative profiling of DNA methylation states in a panel of cancer-associated genes to a case-control study of UADT cancers. Our analyses revealed a high frequency of aberrant hypermethylation of several genes, including MYOD1, CHRNA3 and MTHFR in UADT tumors, whereas CDKN2A was moderately hypermethylated. Among differentially methylated genes, we identified a new gene (the nicotinic acetycholine receptor gene) as target of aberrant hypermethylation in UADT cancers, suggesting that epigenetic deregulation of nicotinic acetycholine receptors in non-neuronal tissues may promote the development of UADT cancers. Importantly, we found that sex and age is strongly associated with the methylation states, whereas tobacco smoking and alcohol intake may also influence the methylation levels in specific genes. This study identifies aberrant DNA methylation patterns in UADT cancers and suggests a potential mechanism by which environmental factors may deregulate key cellular genes involved in tumor suppression and contribute to UADT cancers.

Inactivation of the putative suppressor gene DOK1 by promoter hypermethylation in primary human cancers

The DOK1 gene is a putative tumour suppressor gene located on the human chromosome 2p13 which is frequently rearranged in leukaemia and other human tumours. We previously reported that the DOK1 gene can be mutated and its expression down-regulated in human malignancies. However, the mechanism underlying DOK1 silencing remains largely unknown. We show here that unscheduled silencing of DOK1 expression through aberrant hypermethylation is a frequent event in a variety of human malignancies. DOK1 was found to be silenced in nine head and neck cancer (HNC) cell lines studied and DOK1 CpG hypermethylation correlated with loss of gene expression in these cells. DOK1 expression could be restored via demethylating treatment using 5-aza-2'deoxycytidine. In addition, transduction of cancer cell lines with DOK1 impaired their proliferation, consistent with the critical role of epigenetic silencing of DOK1 in the development and maintenance of malignant cells. We further observed that DOK1 hypermethylation occurs frequently in a variety of primary human neoplasm including solid tumours (93% in HNC, 81% in lung cancer) and haematopoietic malignancy (64% in Burkitt's lymphoma). Control blood samples and exfoliated mouth epithelial cells from healthy individuals showed a low level of DOK1 methylation, suggesting that DOK1 hypermethylation is a tumour specific event. Finally, an inverse correlation was observed between the level of DOK1 gene methylation and its expression in tumour and adjacent non tumour tissues. Thus, hypermethylation of DOK1 is a potentially critical event in human carcinogenesis, and may be a potential cancer biomarker and an attractive target for epigenetic-based therapy.

N-acetyltransferase 2 (NAT2) genotypes, cigarette smoking, and the risk of breast cancer

N-acetyltransferases (NATs) are important catalytic enzymes that metabolize carcinogenic arylamines. NAT2 genotype might modify the role of cigarette smoking, a source of arylamine exposure, in breast cancer. We conducted a nested case-control study to investigate the association between NAT2 genotype, smoking and breast cancer risk among women (110 cases, 113 matched controls) from the CLUE II cohort in Washington County, MD. Compared to women with the slow acetylator genotype, the main effects odds ratios (OR) for NAT2 were 1.4 for the intermediate acetylator genotype (95% confidence limits (CL) 0.7, 2.7) and 3.6 for the homozygous rapid acetylator genotype (95% CL 1.1, 11.4) (P for trend = 0.05). Smoking was associated in the direction of increased breast cancer risk in slow acetylators (e.g., >15 pack-years versus never smokers OR 2.0; 95% CL 0.7, 5.8) but not in rapid acetylators. These associations were not statistically significant in the total study population, but a statistically significant interaction between smoking and NAT2 acetylator status was present in postmenopausal women. The main effect of NAT2 in the direction of increased risk suggests that exposures to NAT2-activated carcinogens other than cigarette smoke may be important in this study population. The results for smoking were consistent with an inactivation role for NAT2 in breast cancer.

Epidemiology, prevention, and early detection of breast cancer

Breast cancer is the most common cancer among women worldwide. Genetic, environmental, and gene-environment interactions are discussed in relation to breast cancer etiology. A major advance in the study of inherited forms of breast cancer occurred with the identification of two genes, BRCA1 and BRCA2, that may account for a majority of inherited forms of breast cancer cases. Hypotheses have been formulated concerning the importance of timing of exposures to environmental agents and a possible role of "xenogenetics" in relation to breast cancer risk. With respect to early detection, regular mammography screening for women aged 50 years and older is clearly associated with a significant reduction in breast cancer mortality, but mammography among women aged 40 to 49 remains controversial. Concerning chemoprevention, the risks and benefits of tamoxifen continue to be clarified, retinoids hold promise, and monoterpenes have emerged as a possible chemopreventive agent.

Breast-conserving surgery and definitive radiation: a comparison between quadrantectomy and local excision with special focus on local-regional control and cosmesis

PURPOSE

Breast-conserving surgery and definitive radiation as an alternative to mastectomy is a well-accepted practice. However, there is limited information addressing the extent of surgical resection. The purpose of this study is to compare the outcome of patients treated with local excision or quadrantectomy, followed by definitive radiation with particular emphasis on local-regional control and cosmetic results.

METHODS AND MATERIALS

Between 1978 and 1989, 425 patients with Stage I and II breast cancer underwent conservative surgery followed by definitive radiation. Fifty-four patients had a local excision and 371 had a quadrantectomy. Median follow-up was 42 months. Axillary dissection (levels I/II) was performed in 317 patients, and of these 126 patients had positive axillary lymph nodes. Radiation consisted of 4500-5000 cGy to the breast with Co60 or 4 MV photons, plus a boost to the tumor site (356/425 patients) for a total dose of 6000-6500 cGy. Treatment of the regional lymph nodes was given to patients with undissected or inadequately dissected axillas and usually to patients with multiple positive lymph nodes. Of the patients with positive lymph nodes, 46% received systemic chemotherapy.

RESULTS

The 5-year actuarial freedom from local-regional recurrence rates for patients treated with local excision and quadrantectomy followed by definitive radiation were 92% and 93%, respectively (p = 0.7). The 5-year actuarial survival rates for local excision and quadrantectomy were as follows: overall (83% and 82%; p = 0.7), cause-specific disease-free (74% and 71%; p = 0.9), and distant disease-free (82% and 76%, p = 0.4). Estimated 10-year results are also presented. Cosmetic analysis required a minimum follow-up of 5 years. In the local excision, 77% of the patients had excellent-good result, compared to 53% following quadrantectomy (p = 0.03). Excluding patients who received chemotherapy, the excellent-good scores were 76% and 57%, respectively (p = 0.1). The most unfavorable cosmetic results were associated with quadrantectomy followed by radiation with boost dose and chemotherapy, excellent-good in 22%.

CONCLUSION

Conservative surgery consisting of local excision or quadrantectomy resulted in comparable local-regional control, overall, disease-free and distant disease-free survival, although cosmetic results were superior in the local excision group.