Correlation between relatives for colorectal cancer mortality in familial adenomatous polyposis

[Evaluation of cancer risk through genetic analysis?]

BACKGROUND

The recent literature of familial cancer, specifically related to germline mutations of RB1, p53, NF1, ATM, BRCA1, Mismatch repair genes and APC is reviewed.

RESULTS AND CONCLUSIONS

Germline mutations do not relate to an increased tumor risk of any single tissue, but instead to spectra of neoplastic diseases. The genetic background plays a major role in modifying the cancer risk. Therefore, mass screening for mutations of single genes seems to be without practical value. Only in combination with an adequate and informative family history can molecular genetic analysis significantly support the care for the individual. Comparison of the data of patients inheriting germline mutations and the experience from the corresponding "knockout" mouse demonstrate that only the p53 and APC knockout mice are useful models of human disease.

Age of onset in familial adenomatous polyposis: heterogeneity within families and among APC mutations

Heterogeneity among and within FAP pedigrees for the age of symptom onset and the age at death from colorectal cancer was studied in a sample of 583 patients of the Italian Polyposis Registry. The among pedigree variation was largely explained by clustering of families in two groups, 'early FAP' (most colorectal cancer deaths below 45 years of age) and 'late FAP' families (most deaths above age 45). The within-family variation was explained by a marked phenomenon of anticipation (15 years per generation, on the average), possibly not due to ascertainment bias. We then considered the pedigrees with identified mutation in the APC gene. Six families shared a common deletion at codon 1309 and showed the early FAP phenotype. Two families shared a mutation at codon 1061 and revealed the late FAP phenotype. Another two families (codons 453 and 302) clustered with the late FAP group, whereas a family with mutation at codon 835 clustered with the early FAP group. We suggest that there are at least two classes of mutations in the APC gene with different consequences at the phenotypic level. It seems that there are several critical points within the APC protein sequence at which truncation causes a more aggressive disease than truncation at other points.

Causes of death and postsurgical survival in familial adenomatous polyposis: results from the Italian Registry. Italian Registry of Familial Polyposis Writing Committee

Causes of death were evaluated among 350 deceased patients with familial adenomatous polyposis (FAP) recorded in the Italian Polyposis Registry: 78.1% were due to colorectal cancer, 9.5% to extracolonic cancer (more than half of the upper gastrointestinal tract), 3.6% to desmoid tumors, and 8.8% to other causes. The age at diagnosis among 604 patients was studied in relation to presence of symptoms at presentation and presence of colonic cancer at surgery. In asymptomatic patients younger than 30 years the risk of colonic cancer was 3.3% and in symptomatic patients older than 40 it was 80%. A life-table analysis showed that postsurgical survival among patients without cancer at colectomy was 68% after 30 years, whereas that of patients with cancer was 41% after 10 years. The alternative prophylactic treatments of total colectomy with ileorectal anastomosis versus total proctocolectomy (IRA vs. IAA) were compared in terms of postsurgical survival. Both treatments showed a survival of 83% after 10 years. The risk of cancer in the rectal stump after IRA was 14.5% after 15 years and 25.2% after 25 years; the corresponding risks of dying from it were 4.3% and 9.3%, respectively.

Familial adenomatous polyposis: mutation at codon 1309 and early onset of colon cancer

The clinical course of familial adenomatous polyposis (FAP) varies considerably between patients. Prediction of the severity of the disease is important in the interest of effective cancer prevention. We examined whether age at diagnosis of FAP due to gastrointestinal symptoms and age at death due to colorectal cancer are related to the site of mutation in the responsible gene. 225 families with FAP were screened for mutations. The deletion of 5 base pairs at codon 1309 within exon 15 (known to be the most common mutation) was identified in 20 families; other mutations within exons 7-15 were found in 49 families. In patients with the 5 base-pair deletion at codon 1309, gastrointestinal symptoms and death from colorectal cancer occurred about 10 years earlier than in patients with other mutations. The 1309 mutation leads to development of colonic polyps at a younger age, thus giving rise to an earlier malignant transformation. This relationship should be taken into account in strategies for preventing cancer in patients with FAP.