Cancer risk in the relatives of patients with nasopharyngeal carcinoma—a register-based cohort study in Sweden.
BACKGROUND
Little is known about cancer susceptibility among relatives of nasopharyngeal carcinoma (NPC) patients in non-endemic areas. We conducted a register-based cohort study to assess the relative risks (RRs) of cancer in families of NPC probands in Sweden.


METHODS
By linking 11,602,616 Swedish-born individuals (defined as 'general population') identified from national censuses to the Swedish Cancer Register and Multi-Generation Register, we identified 9157 relatives (3645 first-degree and 5512 second-degree) of 1211 NPC probands. Cancer incidence during 1961-2009 was ascertained through the Cancer Register. Relative risks of cancer in the relatives of NPC probands, compared with the rest of the general population, were calculated from Poisson regression models.


RESULTS
First-degree relatives had higher risks of NPC (N=2, RR=4.29, 95% confidence interval (CI)=1.07 to 17.17) and cancers of the larynx (N=5, RR=2.53, 95% CI=1.05 to 6.09), prostate (N=76, RR=1.35, 95% CI=1.07 to 1.68), and thyroid (N=10, RR=2.44, 95% CI=1.31 to 4.53) than the rest of the general population. In addition, a raised risk of cancer of the salivary glands was observed among first-degree relatives of probands with undifferentiated NPC (N=2, RR=6.64, 95% CI=1.66 to 26.57). In contrast, a decreased risk of colorectal cancer was observed in first- and second-degree relatives (N=43, RR=0.71, 95% CI=0.53 to 0.96).


CONCLUSIONS
The increased risk of NPC and certain other cancers among first-degree relatives may be explained by shared genetic and environmental risk factors, the latter including Epstein-Barr virus infection and smoking or by increased diagnostic intensity.
Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden.
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Liu
Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden.
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Fang
1] Exponent, Inc., Health Sciences Practice, 149 Commonwealth Drive, Menlo Park, CA, USA [2] Division of Epidemiology, Department of Health Research and Policy, Stanford University School of Medicine, Stanford, CA, USA.
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Chang
Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden.
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Ye
D000293:Adolescent; D000328:Adult; D000368:Aged; D002277:Carcinoma; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D020031:Epstein-Barr Virus Infections / Q000453:epidemiology* / Q000473:pathology; D005190:Family; D005260:Female; D020022:Genetic Predisposition to Disease; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D008875:Middle Aged; D000077274:Nasopharyngeal Carcinoma; D009303:Nasopharyngeal Neoplasms / Q000453:epidemiology* / Q000473:pathology; D012307:Risk Factors; D013548:Sweden