A population-based study of cancer incidence in twins and in children with congenital malformations or low birth weight, Norway, 1967-1980.

The incidence of childhood cancer in twins, in children with congenital malformations diagnosed at birth, and in children of low birth weight was investigated and compared with that in the total population of Norway born live from 1967-1979. Only the malformation group had a significantly increased rate of total cancer (28.3/100,000 person-years) compared with the population (14.6/100,000). The excess cancer appeared to be limited to children with Down's syndrome or a central nervous system defect, who most frequently developed leukemia or central nervous system tumors, respectively. The rates of total cancer in children of low birth weight (9.3/100,000) and in twins (13.0/100,000) were close to expected. However, twins had a significantly increased rate of renal cancer (rate ratio = 4.1). The documented associations between cancers and congenital malformations are suggestive of some common etiologic factors which warrant further studies for their identification and for elucidating possible means of prevention.