Breast cancer

Question 1

What are some of the common risk factors for developing breast cancer?

Answer 1

Age
Genetics (incl. family history)
Exposure to risk factors (e.g. weight, alcohol consumption, use of HRT)

Question 2

What is the strongest risk factor for developing breast cancer?

Answer 2

Family history: individual risk increases with increasing no. of affected relatives and a decreasing age of diagnosis.

15-20% of breast cancer cases are familial (=significant FH)

5-10% are hereditary (=predisposition inherited in AD manner)

Question 3

What are the criteria for suspecting hereditary breast cancer caused by pathogenic BRCA1/2 variant?

Answer 3

• Early onset (<50yrs)
• Two or more breast primaries
• Breast/ovarian in a single individual
• Breast/ovarian in close relatives from same side of family
• At risk populations (e.g. Ashkenazi)
• Family with confirmed BRCA1/2
• Male breast cancer
• Ovarian cancer at any age

Question 4

What things can complicate a clinical diagnosis of hereditary breast cancer?

Answer 4

• Incomplete penetrance
• High prev. of sporadic BC
• Phenocopies (family members developing different cancers)

Question 5

What are some examples of breast cancer probability models?

Answer 5

Myriad II
BRCAPRO
BOADICEA

Question 6

What do breast cancer probability models do?

Answer 6

Determine the likelihood that an individual or family has a BRCA1/2 variant.

All have their own limitations and won’t identify all at risk families.

Question 7

How do breast cancer probability models link to breast cancer screening?

Answer 7

NICE guidance: unaffected individuals whose prior risk of having a BRCA variant is 10% or more qualify for screening

Question 8

What do NICE guidelines state about BRCA testing for individuals who have cancer?

Answer 8

Should be offered to all individuals under 50 who have triple negative breast cancer regardless of FH

Question 9

What is HBOC syndrome?

Answer 9

Hereditary breast and ovarian cancer syndrome - caused by pathogenic variants in BRCA1/2.

Associated with increased risk of early onset BC, ovarian, pancreatic and prostrate cancer and melanoma.

Accounts for 5-7% of all BC.

Incomplete penetrance (lifetime risk highest for breast then ovarian).

Question 10

What are some of the key stats about BRCA1 pathogenic variants and disease?

Answer 10

• ~66% of HBOC syndrome
• 10-20% of women with triple neg BC
• Age of breast/ovarian diagnosis sig. younger than general pop

Question 11

What are some of the key stats about BRCA2 pathogenic variants and disease?

Answer 11

• ~34% of HBOC syndrome
• Risks from BRCA2 wider ranging/more variable than BRCA1
• Increased risk of pancreatic/melanoma

Question 12

Describe the main protein function of BRCA1/2.

Answer 12

Both have roles in DNA repair including homologous recombination of double-stranded DNA breaks and nucleotide excision repair.

BRCA1 forms complexes with BARD1 and localises at sites of DNA damage with BRCA2/RAD51 (mediate homologous recombination).

Question 13

Describe additional functions/theories on BRCA1/2.

Answer 13

Loss of function of BRCA1 results in defects in DNA repair, defects in transcription, abnormal centrosome duplication, defective G2/M cell cycle checkpoint regulation, impaired spindle checkpoint, and chromosome damage.

BRCA2 is transcribed in late G1 phase and remains elevated in S phase, indicating a role in DNA synthesis

BRCA1 is expressed in most tissues and cell types analyzed, suggesting that it is not the gene expression pattern that leads to the tissue-restricted phenotype of breast and ovarian cancer.

Question 14

Provide some details on the mutation spectrum of BRCA1/2

Answer 14

• Majority = nonsense/frameshift
• ~10% large rearrangements, whole exon dels and smaller dups/dels
• Founder mutations exist in diff. populations (e.g. 1 in 40 of the Ashkenazi pop have one of three founder variants)
• Genotype/phenotype correlations reported but not used in clinical practice (E.g. BC risk lower for BRCA1 variants in central region vs 5’)

Question 15

Outline the testing strategy for BRCA1/2

Answer 15

• Sequence analysis of coding exons, intron/exon boundaries and dosage analysis (NGS does both)
• Targeted screening may be more appropriate for some (e.g. Ashkenazi)
• Testing for familial variants available to affected/at risk individuals
• Unaffected individuals can be screened if DNA not available from affected family member

Question 16

What are the downsides to using FFPE for BRCA1/2 screening?

Answer 16

Sensitivity may be lower compared to a germline sample (e.g. dosage analysis not possible)

Question 17

What can be done to help clarify the significance of if a VUS identified through BRCA1/2 screening?

Answer 17

• Cosegregation studies (caveats = phenocopies/incomplete penetrance)
• Looking for LoH in tumour DNA (in majority of BRCA tumours the WT allele is found to be deleted so finding LoH in the tumour increases confidence in the VUS)

Question 18

What are some of the ethical issues arising through BRCA screening?

Answer 18

• Age of onset and severity is very variable. Treatment may be mastectomy or increased screening. Must be made aware of the risk of developing cancer to make a choice.
• Prenatal testing and testing of minors not usually offered.
• Individual with pathogenic variant may not disclose this to other family members, who then cannot also be tested.
• Some family members may choose not to be tested but their genotype will be indirectly determined through testing of other family members.
• Careful genetic counselling is required

Question 19

What are the main treatment options for breast cancer?

Answer 19

Surgery
Chemo
Radiotherapy
Hormonal/endocrine therapy
Targeted cancer drugs

Question 20

Give examples of a targeted cancer drugs that can be used for breast cancer.

Answer 20

Trastuzumab for HER2-positive tumours (not used for BRCA1/2-related cancers as most are HER2-negative).

Tamoxifen for oestrogen receptor positive BC (competitively binds oestrogen receptors).

Question 21

PARP inhibitors are an example of synthetic lethality when used for breast cancer treatment. Provide an overview of how these work.

Answer 21

PARP-1 is an enzyme that repairs single-strand DNA breaks by base-excision repair.

Inhibition of PARP-1 leads to the formation of double-strand breaks due to no longer able to repair single-strand breaks effectively.

In BRCA1/2 null cells, these double-strand breaks can’t be repaired therefore PARP inhibition leads to apoptosis of cancer cells.

Examples: Olaparib - US approved for treatment of metastatic BC in BRCA patients. Some are used in UK for ovarian cancer with trials underway in context of BC.

Question 22

Name 6x cancer predisposition syndromes that include an increased risk of BC

Answer 22

1. Li-Fraumeni syndrome (70% TP53)
2. Peutz-Jeghers syndrome (STK11)
3. Cowden syndrome (PTEN)
4. Hereditary diffuse gastric cancer (30-50% CDH1)
5. Neurofibromatosis type 1 (NF1)
6. Nijmegen breakage syndrome (AR; NBN)

Question 23

BRCA1/2 are the most common genes but what are some of the other lower penetrance genes now included as part of testing?

Answer 23

PALB2
CHEK2*
ATM*
RAD51C
RAD51D

These plus BRCA1/2 are included for ‘R208 breast/ovarian cancer’ testing.

TP53, PTEN and STK11 were also included in UK Cancer Genetics Group consensus panel as genes with sufficient evidence for clinical utility.

*only report truncating variants

Question 24

Can polygenic risk scores be useful in breast cancer?

Answer 24

GWAS have identified identified numerous SNPs associated with increased BC risk.

Each expected to impact to a minor extent on individual risk.

Polygenic risk scores based on larger numbers of associated SNPs have successfully demonstrated an ability to stratify breast cancer risk in a number of populations.

These SNPs can also modify risk in individuals with pathogenic variants in known cancer predisposition genes so polygenic risk scores can also be used to modify estimated BC risks in these scenarios.

Question 25

What are the main two issues with including moderate-low penetrance genes on BC screens?

Answer 25

1. Finding a pathogenic variant in a moderate risk gene in the context of a high-risk FH may not account for all the risk in the family.
2. Inclusion of low penetrance genes may lead to difficulties where the clinical consequences of a variant are unclear and no clinical decisions can be made on their presence/absence.

Question 26

What are some of the current/future developments in breast cancer testing/treatment?

Answer 26

Circulating cell-free DNA (cfDNA) is being investigated as a liquid biopsy for:
1. Real time management of cancer
2. Genetic profiling of tumours to enhance individualised treatment

Various research projects/clinical trials ongoing, incl. looking at BC causes and risk factors, preventative drug treatments, chemotherapy, targeted drug therapies and screening improvements.