Testing for mutations in the BRCA1 and BRCA2 genes among high-risk breast cancer patients has become a routine practice among clinical geneticists. Unfortunately, however, the genetic background of a majority of the cases coming to the clinics remains currently unexplained, making genetic counseling rather challenging. In recent years it has become evident world-wide that also women carrying a heterozygous germline mutation in PALB2 are at significantly increased risk of getting breast cancer. We have previously studied the clinical as well as biological impact of the PALB2 c.1592delT founder mutation occurring in about 1% of Finnish breast cancer patients unselected for their family history of disease, and our results demonstrated a 40% increased breast cancer risk by age 70 for female mutation carriers. Thus, this relatively common mutation in PALB2 is associated with a high risk of developing breast cancer. The aim of the current study was to analyze whether female index individuals of breast cancer families who had tested negative for germline mutations in BRCA1/BRCA2 as part of genetic counseling services should be offered mutation testing for PALB2 c.1592delT.
The study cohort consisted of altogether 223 individuals who had contacted the Department of Clinical Genetics at the Oulu University Hospital in Finland between the years 1997 and 2011 for counseling on hereditary breast and/or ovarian cancer risk. 101 of them met our inclusion criteria. Of these, 10 persons were now deceased, but 6 of them had participated in one of our previous studies on PALB2. Seventy (77%) of the remaining 91 persons responded positively to our study invitation. Chart review of updated pedigree data led to the exclusion of 14 further individuals not meeting the selection criteria.
Of the 56 alive affected female individuals screened for PALB2 c.1592delT, altogether two (3.6%) tested positive for this mutation. In addition, of the previously tested but now deceased 6 persons eligible for the current study, one more mutation carrier was observed. Therefore, overall 4.8% (3/62) of the tested individuals belonging to the Northern Finnish 1997–2011 study cohort turned out to be carriers of the PALB2 c.1592delT allele.
Given the potential benefits versus harms of this testing, the result of our study suggest that PALB2 c.1592delT should be a routine part of the genetic counseling protocol for Finnish high-risk breast cancer cases tested negative for mutations in BRCA1/BRCA2.
Keywords: Hereditary breast cancer predisposition, PALB2, Genetic counseling