Characterization of the HER2 status in BRCA-mutated breast cancer: a single institutional series and systematic review with pooled analysis.

BACKGROUND: Pathogenic variants (PVs) in BRCA1/2 genes account for ∼6% of breast and 20% of ovarian cancers. Most breast tumors developed by BRCA1 carriers are triple negative. BRCA2 tumors have similar rates of estrogen receptor positivity as sporadic controls but are less likely to be human epidermal growth factor receptor 2 (HER2)-positive. Prevalence of HER2 positivity among breast cancers (BCs) in BRCA1/2 mutation carriers is poorly and variably described, ranging from 0% to 10% and 0% to 13% in BRCA1 and BRCA2 carriers, respectively. PATIENTS AND METHODS: We assessed the prevalence of HER2 positivity among a single institutional cohort of 398 BCs developed in carriers of BRCA1/2 PVs (240 BRCA1, 158 BRCA2). Subsequently, a systematic review of the literature and pooled analysis was carried out. RESULTS: In our series we found a 7% HER2 positivity rate among all first BRCA1/2 BCs overall. In BRCA1 carriers, 5.4% of BCs were HER2-positive compared with 9.5% in BRCA2-mutated patients. Among bilateral BCs, HER2-positive cases were 15.2% in the BRCA1 group and 23.1% in the BRCA2 group. Notably, six BRCA1 and eight BRCA2 carriers showed discordant HER2 status between BC and bilateral BC (23.7%, 14/59). The systematic review included 21 083 BRCA1/2 patients from 73 eligible studies. The pooled rate of BRCAmut/HER2-positive BCs is 9.1% (95% confidence interval 7.3% to 11.2%). BRCA1 and BRCA2 when reported as separate data ranged from 0% to 33.3% (mean 8.3%) and from 0% to 86% (mean 10.3%), respectively. CONCLUSIONS: As compared with sporadic cases, BCs occurring in BRCA1 and/or BRCA2 PVs carriers are less frequently HER2-positive. Prevalence of HER2 positivity in our series was consistent with pooled analysis and did not exceed 10%. Although not common, co-existence of BRCA mutations and HER2 overexpression and/or gene amplification should be acknowledged. More research is needed to better characterize this subgroup of patients who should not be excluded a priori from clinical trials of targeted therapy for BRCA1/2-driven cancers.

The psychological impact of breast and ovarian cancer preventive options in BRCA1 and BRCA2 mutation carriers.

This study was performed to describe the impact of preventive options on the psychological condition of BRCA1/BRCA2 carriers. A sample of 52 cancer-affected (C-A) and 27 cancer-unaffected (C-UN) women were enrolled after gene test disclosure (T0). Psychological evaluations were performed at T0 and 15 months later (T1). The surgical options were more likely to be chosen in C-A women (62%), although a consistent proportion of C-UN women (30%) also opt for these preventive measures. At the baseline, both samples had average anxiety and depression scores below the cut-off value, restrained average cancer worry scores and a risk perception consistent with the risk percentage provided during genetic counselling. The longitudinal results indicated no clinically meaningful variations in the anxiety and depression scores in either of the two samples. Statistically significant reductions in cancer-risk perception emerged in women who chose surgery in both C-A and C-UN women. In BRCA1/BRCA2 mutation carriers, surveillance does not influence their initial psychological condition, whereas prophylactic surgery has a significant impact in reducing the perceived risk and worry about getting sick. C-A and C-UN women have to be considered as two separate populations of BRCA mutation carriers requiring personalized approaches to risk management.

An evaluation of the polymorphisms Ins16bp and Arg72Pro in p53 as breast cancer risk modifiers in BRCA1 and BRCA2 mutation carriers.

The close functional relationship between p53 and the breast cancer susceptibility genes BRCA1 and BRCA2 has promoted the investigation of various polymorphisms in the p53 gene as possible risk modifiers in BRCA1/2 mutation carriers. Specifically, two polymorphisms in p53, c.97-147ins16bp and p.Arg72Pro have been analysed as putative breast cancer susceptibility variants, and it has been recently reported that a p53 haplotype combining the absence of the 16-bp insertion and the presence of proline at codon 72 (No Ins-72Pro) was associated with an earlier age at the onset of the first primary tumour in BRCA2 mutation carriers in the Spanish population. In this study, we have evaluated this association in a series of 2932 BRCA1/2 mutation carriers from the Consortium of Investigators of Modifiers of BRCA1 and BRCA2.

Reconstructing the genealogy of a BRCA1 founder mutation by phylogenetic analysis.

Estimating the age of founder mutations may contribute to improve our knowledge of population genetics and evolutionary history of diseases. Previous haplotype analysis suggested that the BRCA1*1499insA mutation was a founder allele, probably originated in Tuscany (Italy). Here, we collected additional pedigrees carrying this mutation, and applied a phylogenetic method for estimating mutation age. A chromosome segment of about 25 cM, including 37 short tandem repeats (STRs) on both sides of the BRCA1 gene (DeCode map), was typed in 50 subjects (28 mutation carriers) from 14 unrelated families. The time to the most recent common ancestor (MRCA) of the mutation carriers was estimated by the length of the shared haplotype between all possible pairs of individuals. A function relating the length of the shared haplotype to the time to the MRCA was obtained by a computer simulation. This approach gives results comparable with those of other existing mutation-dating methods, but does not depend explicitly on population-specific parameters such as allele frequencies, provides narrower confidence intervals (CI), and allows one to build an extended genealogical tree of all mutation carriers. The 1499insA mutation shared by the investigated subjects was estimated to be present in an individual living about 30 generations ago (95% CL 22-56), or 750 years (95% CL 550-1,400).

Use of intercross outbred mice and single nucleotide polymorphisms to map skin cancer modifier loci.

Car-R and Car-S outbred mouse lines, phenotypically selected for resistance and susceptibility to skin carcinogenesis respectively, show significant linkage disequilibrium (LD) at genetic markers mapping on chromosomal regions where skin cancer modifier loci (Skts3, Skts1, and Psl1 on Chrs 5, 7, and 9 respectively) have been mapped in standard crosses. Analysis of these regions for genetic linkage with skin cancer phenotypes in 245 (Car-R x Car-S)F2 intercross mice, by using single nucleotide polymorphisms (SNPs), revealed significant linkage at a possible allelic form of the Skts1 locus, whose mapping region was shortened to a <5.5-cM interval near the Tyr locus. The Car-derived Skts1 locus was linked with papilloma multiplicity and latency by a recessive inheritance of the susceptibility allele. Putative loci on Chr 5 (Skts3) and 9 (Psl1) showed no significant linkage. These results point to the important role of the Stks1 locus in mouse skin tumorigenesis in independent crosses. The shortened Skts1 mapping region should facilitate the identification of candidate genes.

A cancer modifier role for parathyroid hormone-related protein.

The parathyroid hormone-related protein (PTHrP) gene (Pthlh) maps in the distal region of mouse chromosome 6 that contains a quantitative trait locus associated with genetic predisposition to skin tumorigenesis. Here, we report a genetic polymorphism located in the osteostatin encoding region of the Pthlh gene and that produces Thr/ Pro PTHrP variants. PthlhThr and PthlhPro alleles were significantly linked with resistance and susceptibility to skin carcinogenesis in phenotypically selected Car-R and Car-S outbred mice. Transfection of human NCI-H520 squamous cell carcinoma cells with the PthlhPro allele resulted in cells growing in clusters, tending to pile up, and growing at a significantly faster rate in nude mice than non-transfected and PthlhThr-transfected cells. These results point to the role of the Pthlh gene as a cancer modifier gene in skin tumorigenesis.

Mapping of melanoma modifier loci in RET transgenic mice.

Transgenic mice carrying the RET oncogene under the control of the metallothionein promoter exhibit severe pigmentation of the whole skin and melanocytic tumors. The genetic background influences melanoma development in RET mice; founder mice crossed with BALB/c mice show decreased incidence and increased latency of melanocytic tumors, whereas progeny of C57BL/6 mice show the opposite effect. Using partially congenic RET mice on a C57BL/6 genetic background (N3/RET mice), we studied genetic linkage in (N3/RETxBALB/c)xN3/RET backcross mice. We mapped three melanoma modifier loci, on chromosome 1 (Melm1 and Melm2) and chromosome 11 (Melm3), that are linked with early melanoma incidence and latency. Mapping of Melm loci and of five additional regions on chromosomes 6, 8, 9, 12, and 13 indicated allelic imbalance in N3/RET mice, with a significant excess of BALB/c alleles, suggesting the presence of additional putative melanoma modifier loci on these chromosomes.

Linkage disequilibrium and haplotype mapping of a skin cancer susceptibility locus in outbred mice.

Car-R (carcinogenesis-resistant) and Car-S (carcinogenesis-susceptible) outbred mice, obtained by phenotypic selection from an initial intercross of eight inbred strains, show a >100-fold difference in their susceptibility to two-stage skin tumorigenesis. We found that the lines carry a high degree of genetic polymorphism. with an average heterozygosity of 0.39. This polymorphism allowed the use of linkage disequilibrium (LD) and haplotype analysis for the mapping of a skin cancer modifier locus on Chr 7, in a short region of 6 cM, around the Tyr gene. Car-S mice inherited the susceptibility allele at this locus from the A/J, BALB/c, SJL/J, and SWR/J strains. Our results demonstrate the feasibility and usefulness of mapping disease genes by LD in phenotypically selected, genetically heterogeneous animals.

LINE-1 elements at the sites of molecular rearrangements in Alport syndrome-diffuse leiomyomatosis.

Deletions encompassing the 5' termini of the paired type IV collagen genes COL4A5 and COL4A6 on chromosome Xq22 give rise to Alport syndrome (AS) and associated diffuse leiomyomatosis (DL), a syndrome of disseminated smooth-muscle tumors involving the esophagus, large airways, and female reproductive tract. In this study, we report isolation and characterization of two deletion junctions. The first, in a patient described elsewhere, arose by a nonhomologous recombination event fusing a LINE-1 (L1) repetitive element in intron 1 of COL4A5 to intron 2 of COL4A6, resulting in a 13.4-kb deletion. The second, in a previously undescribed family, arose by unequal homologous recombination between the same L1 and a colinear L1 element in intron 2 of COL4A6, resulting in a>40-kb deletion. L1 elements have contributed to the emergence of this locus as a site of frequent recombinations by diverse mechanisms. These give rise to AS-DL by disruption of type IV collagen and perhaps other as yet unidentified genes, evidenced by deletions as small as 13.4 kb.

Perinatal lethality with kidney and pancreas defects in mice with a targetted Pkd1 mutation.

PKD1 is the most common site for mutations in human autosomal dominant polycystic kidney disease (ADPKD). ADPKD is characterized by progressive replacement of kidney tissue by epithelial cysts and eventual renal failure. Hepatic and pancreatic cysts are also common. The PKD1 protein, polycystin, is a cell-surface protein of unknown function that is widely expressed in epithelia and in vascular smooth muscle and myocardium. None of the genetic forms of murine polycystic disease map to the murine Pkd1 locus. We introduced into mice by homologous recombination a Pkd1 truncation mutation, Pkd1-, that mimics a mutation found in ADPKD. Pkd1- heterozygotes have no discernible phenotype, whereas homozygotes die during the perinatal period with massively enlarged cystic kidneys, pancreatic ductal cysts and pulmonary hypoplasia. Renal cyst formation begins at embryonic day 15.5 (E15.5) in proximal tubules and progresses rapidly to replace the entire renal parenchyma. The timing of cyst formation indicates that full-length polycystin is required for normal morphogenesis during elongation and maturation of tubular structures in the kidney and pancreas.

Identification and localization of polycystin, the PKD1 gene product.

Polycystin, the product of autosomal dominant polycystic kidney disease (ADPKD) 1 gene (PKD1) is the cardinal member of a novel class of proteins. As a first step towards elucidating the function of polycystin and the pathogenesis of ADPKD, three types of information were collected in the current study: the subcellular localization of polycystin, the spatial and temporal distribution of the protein within normal tissues and the effects of ADPKD mutations on the pattern of expression in affected tissues. Antisera directed against a synthetic peptide and two recombinant proteins of different domains of polycystin revealed the presence of an approximately 400-kD protein (polycystin) in the membrane fractions of normal fetal, adult, and ADPKD kidneys. Immunohistological studies localized polycystin to renal tubular epithelia, hepatic bile ductules, and pancreatic ducts, all sites of cystic changes in ADPKD, as well as in tissues such as skin that are not known to be affected in ADPKD. By electron microscopy, polycystin was predominantly associated with plasma membranes. Polycystin was significantly less abundant in adult than in fetal epithelia. In contrast, polycystin was overexpressed in most, but not all, cysts in ADPKD kidneys.

Comparative distribution of the alpha 1(IV), alpha 5(IV), and alpha 6(IV) collagen chains in normal human adult and fetal tissues and in kidneys from X-linked Alport syndrome patients.

We have shown previously that the 5' ends of the genes for the alpha 5(IV) and alpha 6(IV) collagen chains lie head-to-head on Xq22 and are deleted in patients with Alport syndrome (AS)-associated diffuse leiomyomatosis. In this study, we raised a rabbit anti-human alpha 6(IV)chain antibody, demonstrated its specificity by the analysis of recombinant NC1 domains af all six type IV chains, and studied the distribution of the alpha 6(IV) chain in relation to the alpha 1(IV) and alpha 5(IV) chains in human adult and fetal tissues involved in AS and diffuse leiomyomatosis. The alpha 6(IV) chain colocalizes with the alpha 5(IV) chain in basement membranes (BMs) of many tissues, but not in glomerular BM. These data exclude the alpha 6(IV) chain as a site for AS mutations. The head-to-head genomic pairing of the alpha 5(IV) and alpha 6 (IV) genes implies coordinate transcription of the two genes. Differential localization of the alpha 5(IV) and alpha 6(IV) chains shows that the two chains are not always coordinately regulated. The alpha 6(IV) chain, together with the alpha 3(IV)-alpha 5(IV) chains, was absent from all renal BMs in eight patients with X-linked AS while the alpha 1(IV) and alpha 2(IV) chains were increased. The data support the existence of two independent collagen networks, one for the alpha 3(IV)-alpha 6(IV) chains and one for the alpha 1(IV) and alpha 2(IV) chains.

Gene linkage analysis and DNA based detection of autosomal dominant polycystic kidney disease (ADPKD) in a newborn infant. Case report.

Bilateral polycystic kidneys were detected by ultrasound at 23 weeks gestation in a male fetus. Bilateral renal cysts were subsequently also found in the asymptomatic propositus' mother and grandmother, suggesting the diagnosis of autosomal dominant polycystic kidney disease (ADPKD). The renal ultrasonograms showed cortical cysts with normal or decreased-sized kidneys. Renal function was normal. Seven available members of the family were genotyped for flanking DNA markers tightly linked to the PKD1 gene on chromosome 16p, and for a polymorphism close to a second putative disease gene (PKD2) on chromosome 2. The genetic linkage approach allowed us to detect with a high degree of accuracy the ADPKD1 at risk chromosome in the three patients, as well as in a 28-year-old unaffected female. This report illustrates the feasibility and the usefulness of recent molecular genetic strategies for diagnostic purposes in ADPKD, especially when clinical and radiological data are atypical. Furthermore, it also confirms that early or very early onset forms of the disease are not uncommon, and should be considered in the differential diagnosis of childhood cystic disease.