IJE Advance Access published online on June 5, 2007
International Journal of Epidemiology, doi:10.1093/ije/dym115
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Letter to the Editor |
Parental age and risk of acute lymphocytic leukaemia and embryonal tumours in the Piedmont Region, Italy
1Cancer Epidemiology Unit, Childhood Cancer Registry of Piedmont, CeRMS and CPO Piemonte, University of Turin, Italy.
2Division of Paediatrics, Department of Medical Sciences, University of Eastern Piedmont at Novara, Italy.
3Unit of Medical Statistics and Epidemiology, Department of Medical Sciences, University of Eastern Piedmont at Novara, Italy.
*Corresponding author. Cancer Epidemiology Unit, S. Giovanni Hospital and University of Turin, via Santena 7, 10126 Torino, Italy. E-mail: milena.maule{at}cpo.it
Using data from the Swedish Cancer Registry, Yip and colleagues1 have recently shown that advanced parental age might be associated with an increased risk of cancer among children zero to four years old born between 1961 and 2000. They analysed five main cancer types (leukaemia, central nervous system tumours, non-Hodgkin's lymphoma, Wilm's tumours and retinoblastoma) and found a positive association of older paternal age with central nervous system and Wilm's tumours, and older maternal age with leukaemia and retinoblastoma.
Using data from the population-based Childhood Cancer Registry of Piedmont (CCRP), Italy, and the Italian National Institute of Statistics (ISTAT) we have recently analysed the effect of maternal age on temporal trends in the incidence of acute lymphocytic leukaemia (ALL).2 The same sources of data are used here to evaluate, among children younger than five years old, the effect of parental age on the risk of ALL (33% of all malignancies) and embryonal tumours (41% of all malignancies, and 73% of all solid tumours).
Data on incident cases of childhood tumours were extracted from the CCRP, which has recorded incident cases of cancer in children (0–14 years) resident in the region since 1967. The procedures and criteria for inclusion in the CCRP database, follow-up and coding of cancer types have been reported elsewhere.3 We considered incident cases of ALL and embryonal tumours (subtypes of embryonal tumours are listed in Table 1) in children aged zero to four. The year of birth of cases’ parents is included in the CCRP records, whereas the year of birth of parents of all children born in Piedmont in the study period was available as individual anonymous records from ISTAT for children born from 1980 to 1997. Analyses were therefore restricted to this period.
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Relative risks (RRs) for maternal and paternal ages were estimated using log-binomial regression adjusting for sex and year of birth. Paternal and maternal age effects were mutually adjusted.
Out of a population of more than 630 000 children followed-up from birth to age five, we observed 229 cases of ALL and 284 cases of embryonal tumours. Older maternal age was associated with ALL risk, irrespective of adjustment for paternal age (Table 1). Conversely, an apparent association with paternal age disappeared when maternal age was included in the model. Both maternal and paternal ages were independently associated with the risk of embryonal tumours, although the RR estimates were attenuated when both variables were introduced in the model. Subgroup analyses were carried out for cancer types with at least 30 observed cases. The strongest association of paternal age was found with embryonal tumours of the kidney (maternal age-adjusted RR for each 5-year increase in paternal age: 1.29, 95% confidence intervals: 0.98–1.68).
In our study, ALLs were analysed separately since they are the most frequent type of tumour among children aged less than five. Other types of tumours were grouped and analysed together, under the assumption that parental age might have a stronger effect on tumours with an embryonal origin. Maternal age was associated with both leukaemia and embryonal tumour risk, whereas paternal age, which could relate to accumulation of germ cell mutations,4 was associated with embryonal tumours only.
Conflict of interest. None declared.
Acknowledgments
The CCRP is supported by the Piedmont Region. This project was partly supported by the Compagnia di San Paolo/FIRMS, the Italian Association for Cancer Research (AIRC), and MIUR. We thank Dr Marco Dalmasso for providing data on the population of Piedmont. We are grateful to Professor Benedetto Terracini for his valuable comments to the manuscript.
References
1 Yip BH, Pawitan Y, Czene K. Parental age and risk of childhood cancers: a population-based cohort study from Sweden. Int J Epidemiol (2006) 35:1495–503.
2 Maule M, Merletti F, Pastore G, Magnani C, Richiardi L. Effects of maternal age and cohort of birth on incidence time trends of childhood acute lymphoblastic leukemia. Cancer Epidemiol Biomarkers Prev (2007) 16:347–51.
3 Dalmasso P, Pastore G, Zuccolo L, et al. Temporal trends in the incidence of childhood leukemia, lymphomas and solid tumors in north-west Italy, 1967-2001. A report of the Childhood Cancer Registry of Piedmont. Haematologica (2005) 90:1197–204.
4 Thacker PD. Biological clock ticks for men, too: genetic defects linked to sperm of older fathers. JAMA (2004) 291:1683–85.
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