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Background/Objectives : Ductal carcinoma in situ (DCIS) is the most common non-invasive form of breast cancer. It is not clear to what extent DCIS is a part of the hereditary breast/ovarian cancer syndrome caused by BRCA1/2 mutations. Therefore, we investigated the association of BRCA1/2 mutations in patients with DCIS and assessed their impact on survival. Methods : We studied 564 Polish women with DCIS for six alleles in BRCA1 (c.181T>G, c.5266dupC, c.4035delA, c.3700&#95;3704del5, c.68&#95;69del and c.5251C>T) and four in BRCA2 (c.658&#95;659del, c.3847&#95;3848del, c.5946del and c.7913&#95;7917del). To investigate the association of BRCA1/2 founder mutations with DCIS risk, we tested 4702 controls as a reference. To analyze survival, mutation carriers were followed for an average of 110 months. Results : A BRCA1 mutation was present in seven (1.24%) cases and in twenty-two (0.47%) controls (OR = 3.27, 95%CI 1.36 to 7.87, p = 0.01). A BRCA2 mutation was present in eight (1.42%) cases versus six (0.13%) controls (OR = 11.3, 95%CI 3.9 to 32.6, p < 0.0001). Three of the fifteen cases with BRCA1/2 mutations developed invasive ipsilateral or contralateral breast cancer, on average 6 years from the diagnosis of DCIS. There were no deaths reported among the 15 mutation carriers with DCIS. Conclusions : DCIS is a part of the hereditary breast/ovarian cancer syndrome caused by BRCA1/2 mutations. Women with DCIS should receive genetic counseling and testing for BRCA1/2 mutations. BRCA1/2 mutations may predispose women to a better DCIS prognosis, but further studies are needed.

The APOBEC3B gene belongs to a cluster of DNA-editing enzymes on chromosome 22 and encodes an activation-induced cytidine deaminase. A large deletion of APOBEC3B was associated with increased breast cancer risk, but the evidence is inconclusive. To investigate whether or not APOBEC3B is a breast cancer susceptibility gene, we sequenced this gene in 617 Polish patients with hereditary breast cancer. We detected a single recurrent truncating mutation (c.783delG, p.Val262Phefs) in four of the 617 (0.65%) hereditary cases by sequencing. We then genotyped an additional 12,484 women with unselected breast cancer and 3740 cancer-free women for the c.783delG mutation. The APOBEC3B c.783delG allele was detected in 60 (0.48%) unselected cases and 19 (0.51%) controls (OR = 0.95, 95% CI 0.56-1.59, p = 0.94). The allele was present in 8 of 1968 (0.41%) familial breast cancer patients from unselected cases (OR = 0.80, 95% CI 0.35-1.83, p = 0.74). Clinical characteristics of breast tumors in carriers of the APOBEC3B mutation and non-carriers were similar. No cancer type was more frequent in the relatives of mutation carriers than in those of non-carriers. We conclude the APOBEC3B deleterious mutation p.Val262Phefs does not confer breast cancer risk. These data do not support the hypothesis that APOBEC3B is a breast cancer susceptibility gene.

The goal of this study was to estimate the risk of thyroid cancer following breast cancer and to identify therapeutic and genetic risk factors for the development of thyroid cancer after breast cancer. We followed 10,832 breast cancer patients for a mean of 14 years for new cases of thyroid cancer. All women were genotyped for three Polish founder mutations in BRCA1 (C61G, 4153delA, 5382insC) and four mutations in CHEK2 (1100delC, IVS2 + 1G/A, del5395, I157T). Information was collected on chemotherapy, radiotherapy, hormonal therapies, and oophorectomy. Of the 10,832 women, 53 (0.49%) developed a second primary thyroid cancer. Based on Polish population statistics, the expected number was 12.4 (SIR = 4.3). The ten-year risk of developing thyroid cancer was higher in women who carried a CHEK2 mutation (1.5%) than in women who carried no mutation (0.9%). The age-adjusted hazard ratio for developing thyroid cancer was 1.89 (0.46-7.79; p = 0.38) for those with a CHEK2 protein-truncating mutation and 2.75 (1.29-5.85; p = 0.009) for those with a CHEK2 missense mutation.

The current cancer testing gene panels tend to be comprehensive rather than site-specific. BARD1 is one of the genes commonly included in the multi-cancer testing panels. Mutations in BARD1 confer an increase in the risk for breast cancer, but it is not studied whether or not they predispose to prostate cancer. To establish if BARD1 mutations also predispose to prostate cancer, we screened BARD1 in 390 Polish patients with hereditary prostate cancer. No truncating mutations were identified by sequencing. We also genotyped 5715 men with unselected prostate cancer, and 10,252 controls for three recurrent BARD1 variants, including p.Q564X, p.R658C and p.R659=. Neither variant conferred elevated risk of prostate cancer (ORs between 0.84 and 1.15, p -values between 0.57 and 0.93) nor did they influence prostate cancer characteristics or survival. We conclude that men with a BARD1 mutation are not at elevated prostate cancer risk. It is not justified to inform men about increased prostate cancer risk in case of identification of a BARD1 mutation. However, a female relative of a man with a BARD1 mutation may benefit from this information and be tested for the mutation, because BARD1 is a breast cancer susceptibility gene.

Bloom Syndrome is a rare recessive disease which includes a susceptibility to various cancers. It is caused by homozygous mutations of the BLM gene. To investigate whether heterozygous carriers of a BLM mutation are predisposed to breast cancer, we sequenced BLM in 617 patients from Polish families with a strong family history of breast cancer. We detected a founder mutation (c.1642C>T, p.Gln548Ter) in 3 of the 617 breast cancer patients (0.49%) who were sequenced. Then, we genotyped 14,804 unselected breast cancer cases and 4698 cancer-free women for the founder mutation. It was identified in 82 of 14,804 (0.55%) unselected cases and in 26 of 4698 (0.55%) controls (OR = 1.0; 95%CI 0.6-1.6). Clinical characteristics of breast cancers in the BLM mutation carriers and non-carriers were similar. Loss of the wild-type BLM allele was not detected in cancers from the BLM mutation carriers. No cancer type was more common in the relatives of mutation carriers compared to relatives of non-carriers. The BLM founder mutation p.Gln548Ter, which in a homozygous state is a cause of Bloom syndrome, does not appear to predispose to breast cancer in a heterozygous state. The finding casts doubt on the designation of BLM as an autosomal dominant breast cancer susceptibility gene.