SCIENTIFIC REPORT 2010 - 2011 - IOV

Unit. The Unit mission includes collaborative efforts with other
regional hospitals to set up clinical genetic counseling facilities
according to national and international guidelines for the genetic
tests in hereditary breast and ovarian cancer patients. During the
last three years, 577 new breast and ovarian cancer families were
recruited and screened. A total of 760 BRCA1 and BRCA2 tests
were performed using highly comprehensive mutation detection
strategies that cover the entire BRCA1 and BRCA2 mutational
spectra, including major genomic rearrangements. Mutationspecific
tests were offered to eligible relatives of the positive cases,
allowing for the identification of at risk family members who were
counseled and clinically managed according to the result of the
specific test. To date, the number of BRCA1/2 mutation positive
families identified by the Unit from the start of its activity has
raised to 253 for a total of more than 450 carriers of deleterious
mutations.
Results and conclusions. The understanding of the genetic
determinants of the non-informative families is one of the key
goals of our most recent studies. Evaluation of the clinical relevance
of BRCA1 and BRCA2 sequence variants of unknown pathogenic
significance, currently identified in 10-20% of individuals
undergoing BRCA1/2 genetic testing, represents a valid possibility
of increasing the number of informative tests. To address this
problem we have used a combination of bioinformatic tools,
based either on the predicted splicing effect, or the evolutionary
conservation as well as the chemical/physical properties of
aminoacid changes, and identified 12 unclassified variants with a
high probability of being deleterious. Two of these variants have
already reached classification: the BRCA c.301+6T>C classified
as likely neutral or of low clinical significance and the BRCA1
c.5074G>C p.Asp1692His which was previously mis-classified as
a missense mutation. Using in vitro transcript assays we showed
that this is a splicing mutation leading a cryptic splice site 153
nucleotides in intron 17 of the BRCA1 gene that brings about
a frame-shift in the protein and a premature termination codon.
For the remaining ten variants we are currently collecting data and
family members to be used in a multifactorial likelihood model,
that integrates independent sources of evidence of disease causality
derived from: co-segregation of the disease with the variant, LOH,
and histopathology data on available tumor specimens, as well as
evolutionary conservation and molecular epidemiology analyses.
A second research line focuses on the identification of other
susceptibility genes with moderate-low penetrance. While
these genes are more likely to be critical in the development
of the sporadic breast or ovarian cancer, at the same time they
provide the tools for better defining the risk profile of BRCA1
and BRCA2 carriers. To address these studies with a sufficiently
powered approach, the Unit joined in 2007 the Consortium of
Investigators of Modifiers of BRCA1/2 (CIMBA) that currently
includes about 50 research groups located world-wide and with
a sufficient sample size to allow large scale studies in order to
evaluate reliably the effects of genetic modifiers. By the candidate
gene approach, these studies have so far led to identification
of five loci which modify the risk of breast cancer for BRCA1
mutation carriers (CASP8, TOX3, 2q35, 19p13 and 6q25.1)
and nine loci which modify the risk of breast cancer for BRCA2
mutation carriers (FGFR2, TOX3, MAP3K1, LSP1, 2q35,
SLC4A7, 5p12, ZNF365 and 1p11.2). For the ovarian cancer
risk, one SNP rs3814113 at 9p22.2 was associated with a reduced
risk of cancer among BRCA1 and BRCA2 mutation carriers (HR
= 0.78). BRCA1 mutation carriers with the TT genotype were
predicted to have an ovarian cancer risk to age 80 of 48%, and
those with the CC genotype were predicted to have a risk of 33%.
Two two-staged genome-wide association studies (GWAS) were
also carried out within the Consortium as collaborative projects
using the Affymetrix 6.0 SNP platform. The study of BRCA2
mutation carriers identified several SNP previously associated with
sporadic breast cancer risk and two novel loci on chromosome
20 (rs311499) and chromosome 10 (rs16917302); FGFR2
rs2981575 showed the strongest association with breast cancer
risk (per allele HR = 1.28). Five SNP on 19p13 were associated
with breast cancer risk from the GWAS in BRCA1 carriers. The
five SNP were also associated with triple-negative breast cancers in
a separate study of 2,301 triple-negative cases and 3,949 controls.
Although altogether these variants account for a small proportion
of the variability in the genetic risk of breast cancer (3-6%), it has
been demonstrated that these SNP have implications for absolute
risk prediction in mutation carriers.
familial maliGNaNT mElaNOma
Principal Investigator: Chiara Menin
The studies on the genetics of familial melanoma are developing
along two major lines: a) molecular analysis of constitutive genetic
alterations in high/low penetrance genes which are considered
predisposing to familial melanoma in probands/relatives belonging
THE DEPARTMENTS - DEPARTMENT OF EXPERIMENTAL, LABORATORY AND TRANSLATIONAL ONCOLOGY
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