Transcriptome-wide association study of breast cancer risk by estrogen-receptor status

Previous transcriptome-wide association studies (TWAS) have identified breast cancer risk genes by integrating data from expression quantitative loci and genome-wide association studies (GWAS), but analyses of breast cancer subtype-specific associations have been limited. In this study, we conducted a TWAS using gene expression data from GTEx and summary statistics from the hitherto largest GWAS meta-analysis conducted for breast cancer overall, and by estrogen receptor subtypes (ER+ and ER-). We further compared associations with ER+ and ER- subtypes, using a case-only TWAS approach. We also conducted multigene conditional analyses in regions with multiple TWAS associations. Two genes, STXBP4 and HIST2H2BA, were specifically associated with ER+ but not with ER- breast cancer. We further identified 30 TWAS-significant genes associated with overall breast cancer risk, including four that were not identified in previous studies. Conditional analyses identified single independent breast-cancer gene in three of six regions harboring multiple TWAS-significant genes. Our study provides new information on breast cancer genetics and biology, particularly about genomic differences between ER+ and ER- breast cancer.

Cancer Risks Associated With Germline PALB2 Pathogenic Variants: An International Study of 524 Families

PURPOSE

To estimate age-specific relative and absolute cancer risks of breast cancer and to estimate risks of ovarian, pancreatic, male breast, prostate, and colorectal cancers associated with germline PALB2 pathogenic variants (PVs) because these risks have not been extensively characterized.

METHODS

We analyzed data from 524 families with PALB2 PVs from 21 countries. Complex segregation analysis was used to estimate relative risks (RRs; relative to country-specific population incidences) and absolute risks of cancers. The models allowed for residual familial aggregation of breast and ovarian cancer and were adjusted for the family-specific ascertainment schemes.

RESULTS

We found associations between PALB2 PVs and risk of female breast cancer (RR, 7.18; 95% CI, 5.82 to 8.85; P = 6.5 × 10-76), ovarian cancer (RR, 2.91; 95% CI, 1.40 to 6.04; P = 4.1 × 10-3), pancreatic cancer (RR, 2.37; 95% CI, 1.24 to 4.50; P = 8.7 × 10-3), and male breast cancer (RR, 7.34; 95% CI, 1.28 to 42.18; P = 2.6 × 10-2). There was no evidence for increased risks of prostate or colorectal cancer. The breast cancer RRs declined with age (P for trend = 2.0 × 10-3). After adjusting for family ascertainment, breast cancer risk estimates on the basis of multiple case families were similar to the estimates from families ascertained through population-based studies (P for difference = .41). On the basis of the combined data, the estimated risks to age 80 years were 53% (95% CI, 44% to 63%) for female breast cancer, 5% (95% CI, 2% to 10%) for ovarian cancer, 2%-3% (95% CI females, 1% to 4%; 95% CI males, 2% to 5%) for pancreatic cancer, and 1% (95% CI, 0.2% to 5%) for male breast cancer.

CONCLUSION

These results confirm PALB2 as a major breast cancer susceptibility gene and establish substantial associations between germline PALB2 PVs and ovarian, pancreatic, and male breast cancers. These findings will facilitate incorporation of PALB2 into risk prediction models and optimize the clinical cancer risk management of PALB2 PV carriers.

Genetic, clinical and pathological characteristics of BRCA-associated breast cancer (BC) in Hispanic patients in the United States (US) and Latin America (LatAm)

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Background: Hispanic women with BC present at a younger age, have a higher frequency of BRCA mutations and show a worse incidence-to-mortality ratio than non-Hispanic women. Information regarding the characteristics of BRCA-associated BC in Hispanics is limited. Here, we assess differences in BRCA-associated BC between Hispanic patients in the US and in LatAm. Methods: Hispanic patients from the US and LatAm (Mexico, Colombia, Peru, and Puerto Rico) with a history of BRCA-associated BC enrolled in the Clinical Cancer Genomics Community Research Network registry were included. We compared the genetic, demographic, clinical and pathologic characteristics between Hispanics from the US and LatAm using Fisher’s exact test and x2statistics. Results: Between 1997 and 2016, 3670 Hispanic patients with a history of BC from LatAm (n = 1341) and the US (n = 2329) were identified, of which 490 (13.3%) had a deleterious BRCA mutation. The frequency of BRCA mutations was similar in Hispanics from LatAm (13.8%, n = 185) and the US (13.1%, n = 305). No significant differences were found in the frequency of BRCA1 vs BRCA2 mutations between patients from LatAm (BRCA1 68%, BRCA2 31.8%) and the US (BRCA1 61.3%, BRCA2 39%) (p = .12). The most frequent mutations found in BRCA1 were: ex 9-12del (LatAm n = 24, US n = 15), 185delAG (LatAm n = 13, US n = 18) and 943ins10 (LatAm n = 3, US n = 8), and in BRCA2 3492insT (LatAm n = 3, US n = 28). Mean age at BC diagnosis was 39.1 (SD 9.5) in LatAm and 41.7 (SD 10.6) in the US (p = 0.01). US patients were significantly more likely to present with Stage 0-II BC than those from LatAm (77.1% vs. 47.6%, p < .001). We found no differences in the proportion of hormone receptor positive tumors between patients from LatAm (45%) and the US (47%) (p = .78). Conclusions: The frequency of BRCA-associated BC was similar between Hispanics in LatAm and the US. Women from LatAm with BRCA mutations present at a younger age, as seen for sporadic BC; the causes for this finding warrant further research. Women with BRCA-associated BC in LatAm are more likely to have advanced BC at presentation, which may be a reflection of disparities and barriers in access to care.