Jillian M Birch

There are strong a priori reasons for considering parental smoking behaviour as a risk factor for childhood cancer but case – control studies have found relative risks of mostly only just above one. To investigate this further, self-reported smoking habits in parents of 3838 children with cancer and 7629 control children included in the United Kingdom Childhood Cancer Study (UKCCS) were analysed. Separate analyses were performed for four major groups (leukaemia, lymphoma, central nervous system tumours and other solid tumours) and more detailed diagnostic subgroups by logistic regression. In the four major groups, after adjustment for parental age and deprivation there were nonsignificant trends of increasing risk with number of cigarettes smoked for paternal preconception smoking and nonsignificant trends of decreasing risk for maternal preconception smoking (all P-values for trend >0.05). Among the diagnostic subgroups, a statistically significant increased risk of developing hepatoblastoma was found in children whose mothers smoked preconceptionally (OR=2.68, P=0.02) and strongest (relative to neither parent smoking) for both parents smoking (OR=4.74, P=0.003). This could be a chance result arising from multiple subgroup analysis. Statistically significant negative trends were found for maternal smoking during pregnancy for all diagnoses together (P<0.001) and for most individual groups, but there was evidence of under-reporting of smoking by case mothers. In conclusion, the UKCCS does not provide significant evidence that parental smoking is a risk factor for any of the major groups of childhood cancers.

Tumour and normal tissue from 41 male cases of Wilms' tumour were screened to determine the presence of sequence variants in the glypican 3 (GPC3) gene. Two non-conservative single base changes were present in tumour tissue only. These findings imply a possible role for GPC3 in Wilms' tumour development.

The cancer experience among relatives of an unselected cohort of 402 breast cancer patients was previously reported. Cases and their first degree relatives were flagged at the National Health Service Central Register for continuous notification of cancer registrations and deaths. More than 10 years of follow-up data have been analysed to update cancer risks overall and to estimate breast cancer risk in relatives prospectively according to family history at the time of breast cancer diagnosis in the index case. Significant excesses of breast cancer (RR 2.24, PP=0.039) and bone sarcoma (RR 6.564, P=0.042) overall and soft tissue sarcoma in mothers only (RR 15.44, P=0.001) were found. There was no excess of any other cancer, including ovarian. High breast cancer risk in relatives was associated with young age at diagnosis in the index (index P=0.004). Prospective risk of breast cancer was higher in relatives of index patients who had an affected first degree relative at the time of their diagnosis (no family history, RR 1.87, P=0.012; with a family history, RR 3.72, P=0.015). These prospective risk estimates are valuable in advising relatives of newly diagnosed breast cancer patients.

The spectrum and frequency of cancers associated with germline TP53 mutations are uncertain. To address this issue a cohort of individuals from 28 families with Li-Fraumeni syndrome, segregating germline TP53 mutations was established. Predicted cancers were estimated by applying age, morphology, site and sex-specific UK cancer statistics to person-years at risk. Observed and predicted cancers were compared and two-sided P-values calculated. Cancer types occurring to excess and showing P-values P-values <0.02 and 0.02–0.05 in the second round analyses were considered moderately and weakly associated respectively. Strongly associated cancers were: breast carcinoma, soft tissue sarcomas, osteosarcoma, brain tumours, adrenocortical carcinoma, Wilms' tumour and phyllodes tumour. Carcinoma of pancreas was moderately associated. Leukaemia and neuroblastoma were weakly associated. Other common carcinomas including lung, colon, bladder, prostate, cervix and ovary did not occur to excess. Although breast carcinoma and sarcomas were numerically most frequent, the greatest increases relative to general population rates were in adrenocortical carcinoma and phyllodes tumour. We conclude that germline TP53 mutations do not simply increase general cancer risk. There are tissue-specific effects.

We have previously reported on the analysis of TP53 coding mutations in 12 classic Li-Fraumeni syndrome (LFS) families plus 9 families that were Li-Fraumeni-like (LFL) families (J. M. Birch et al., Cancer Res., 54: 1298-1304, 1994). Mutations were found in 6 of 12 LFS families and in 1 of 9 LFL families. We have now extended these studies to include an additional nine LFS and nine LFL families, and TP53 mutations have been detected in eight of nine LFS families and in three of nine LFL families. Six of the new mutations described here are the same as those previously identified in other Li-Fraumeni families and are missense mutations at codons 245, 248, and 273 (in two families); a nonsense mutation at codon 209; and a mutation at the splice donor site in exon 4. The other five mutations are novel germ-line mutations and include missense mutations at codons 136 and 344, a 2-bp deletion within codon 191, a splice acceptor mutation in intron 3, and a 167-bp deletion of part of exon 1 and intron 1. In addition, we have detected a codon 175 mutation in a family previously reported as TP53 negative. To summarize all of the data from the families we have studied in this and our previous report (J. M. Birch et al., Cancer Res., 54: 1298-1304, 1994), mutations have been detected in 15 of 21 LFS families (71%) and in 4 of 18 LFL families (22%). These figures are somewhat higher than those previously reported by us and others for the frequency of TP53 mutations in LFS and LFL families. This could reflect our analysis of all 11 exons of TP53, including noncoding regions, as well as the use of direct sequencing rather than other less-sensitive mutation detection methods.

We report details of a family with classic Li-Fraumeni syndrome in which there is a mutation in codon 344 of the tumour suppressor gene TP53. Codon 344 is a key residue within the tetramerisation domain, and the amino acid substitution of a proline for a leucine is predicted to have profound implications for tetramerisation and potentially DNA binding. This is the first report of a mutation at this residue in either sporadic tumours or in the germline and the first report of a germline mutation within the tetramerisation domain. The family does not appear to be remarkable in the spectrum of tumours, and there is loss of the wild-type allele in a leiomyosarcoma from the proband. A cell line has been established from the tumour of the proband and cytogenetic and molecular studies carried out, providing an extensive analysis in this family.

The entire coding sequence of the p53 gene was analysed for the presence of mutations in 12 families conforming to a restricted definition of Li-Fraumeni syndrome (classic LFS) and nine families with features of LFS conforming to a broader definition. Mutations were detected in seven families. Six were point mutations with one each affecting codons 175, 180, and 220 and three affecting codon 248. The seventh was a deletion/insertion mutation in exon 4. Germline mutations in p53 were a feature of families which included children with rhabdomyosarcoma and/or adrenal cortical carcinoma. Germline p53 mutations were detected in six of the nine families with such tumors. An analysis of these 7 mutations, together with 34 published examples, showed that more than one-half were transitions at CpG dinucleotides, suggesting that the majority of germline p53 mutations may arise as a result of spontaneous events. The most common cancers occurring in the 41 families with germline p53 mutations, in common with classic LFS, were bone and soft tissue sarcoma, breast cancer, brain tumors, leukemia, and adrenocortical carcinoma, although less than one-half of the probands with germline p53 mutations came from classic LFS families. More than one-half of the cancers overall and nearly one-third of the breast cancers were diagnosed before 30 years of age. These observations have important implications for asymptomatic carriers of germline p53 mutations, and there is a need for international collaboration in the development of protocols for the management of such families.