Hereditary breast cancer – a spectrum of pathogenic mutations and unknown variants of BRCA1 and BRCA2 genes in the Czech Republic: efficiency of testing and clinical follow-up

Background

Germline mutations in the highly penetrant cancer susceptibility genes BRCA1 and BRCA2 cause genetic predisposition to breast and ovarian cancers. Molecular genetic testing of pathogenic mutations in these two genes is an effective method for breast cancer risk prediction. Genetic counselling and testing has been provided to high-risk women in our institute since 1997. Until now 589 probands (580 women and nine men) with breast/ovarian cancer have been tested for BRCA1/2 germline mutations.

Methods

Genetic counselling was performed by a medical geneticist in our institute or in other genetic centres of the Czech Republic. Informed consent was signed in all tested individuals. For genetic testing the non-radioactive protein truncation test of exon 11 of BRCA1 and exons 10 and 11 of BRCA2 were used, followed by heteroduplex analysis of the remaining exons with their splice sites and by sequencing. The frequency of unknown variants was tested in a control group of healthy women older than 60 years without a positive family history of breast/ovarian cancer.

Results

The pathogenic mutation was found in 179 of 589 tested probands (30%), 106 in the BRCA1 gene and 73 in the BRCA2 gene. The frequency of detected mutations was calculated in different categories of family history and in sporadic cases. Mutation was found in 86 of 213 (overall 40.4%, hereditary ovarian cancer [HOC] + hereditary breast and ovarian cancers [HBOC] 63.6%, hereditary breast cancer [HBC] 30.8%) families with three or more cases of breast or ovarian cancer (bilateral cancer was counted as two cases), in 66 of 258 (overall 25.6%, HOC + HBOC 46.8%, HBC 22.1%) families with two breast or ovarian cases, in four of 14 (28.6%) probands with sporadic bilateral breast cancer first diagnosed before age 50, in three of seven (42.9%) women with sporadic bilateral ovarian cancer under age 50, in 11 of 12 (91.7%) women with sporadic breast and ovarian cancer diagnosed at any age, in six of 66 (9.1%) women with sporadic unilateral breast cancer before age 40, in zero of 10 women with sporadic unilateral ovarian cancer before age 40, in three of six (50%) males with familial form of breast cancer, and in one of three (33.3%) males with sporadic breast cancer.

There are five most frequent mutations in the Czech population, which represent 56.8% of all mutations found (c.5385dupC, c.3819_3823delGTAAA and c.300T>G in BRCA1; c.8138_8142delCCTTT and c.8765_8766delAG in BRCA2). Overall 14 novel pathogenic mutations were detected, eight of them have been published by our group [1, 2] and the other six mutations have not yet been published. A spectrum of 28 variants (13 in BRCA1 and 15 in BRCA2) with unknown clinical significance was found. The most frequent variant was c.5075G>A, p.M1652I, in the BRCA1 gene (in 22 cases), but the frequency of this variant in a control population was 6.3%. The missense mutation in the BRCA1 gene c.172T>A, p.M18K, was detected three times in HBOC and HBC families, and is very probably pathogenic (localised in a highly conserved structure of the Ring finger domain); it was not detected in a control group. Another two variants were detected in a control population with frequency 1.6%: IVS24/c.9485-16T>C and c.10323delCins11 in the BRCA2 gene.

By predictive testing, positive carrier status was disclosed in 163 individuals of 395 tested. The clinical follow-up was offered to all individuals at high risk. The high-risk clinic at MMCI is following 62 healthy carriers, 139 healthy people at risk, 47 patients–carriers and 29 high-risk patients with negative testing result. From these, 14 patients and three healthy carriers underwent prophylactic mastectomy, 26 patients and four healthy carriers underwent prophylactic adnexectomy. According to the questionnaire for diagnoses of depression CES-D instituted before testing, 51% of women did not report any signs of depression, 27% reported very mild, 14% middle and 8% severe signs of depression. A psychologist in our institute follows 27 women. No severe psychological complications of testing have so far been reported.

Conclusion

Overall, pathogenic mutation was disclosed in 30% of all our tested individuals with familial or sporadic breast (or ovarian) cancer. At least one ovarian cancer in a high-risk family increases twice the likelihood of mutation detection. Fourteen novel mutations and a spectrum of unknown variants were detected. Prophylactic mastectomy is not so frequently accepted by mutation carriers as in Western Europe, but there is an increasing tendency especially in young women. The quality of preventive care in other institutions and the psychosocial influence of genetic testing are now being investigated.