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Abstract Background Risk stratification as a routine part of the NHS Breast Screening Programme (NHSBSP) could provide a better balance of benefits and harms. We developed BC-Predict, to offer women when invited to the NHSBSP, which collects standard risk factor information; mammographic density; and in a sub-sample, a Polygenic Risk Score (PRS). Methods Risk prediction was estimated primarily from self-reported questionnaires and mammographic density using the Tyrer–Cuzick risk model. Women eligible for NHSBSP were recruited. BC-Predict produced risk feedback letters, inviting women at high risk (≥8% 10-year) or moderate risk (≥5– Results Overall uptake of BC-Predict in screening attendees was 16.9% with 2472 consenting to the study; 76.8% of those received risk feedback within the 8-week timeframe. Recruitment was 63.2% with an onsite recruiter and paper questionnaire compared to P Discussion We have shown that a real-time offer of breast cancer risk information (including both mammographic density and PRS) is feasible and can be delivered in reasonable time, although uptake requires personal contact. Preventive medication uptake in women newly identified at high risk is high and could improve the cost-effectiveness of risk stratification. Trial registration Retrospectively registered with clinicaltrials.gov (NCT04359420).

There is great promise in breast cancer risk stratification to target screening and prevention. It is unclear whether adding gene panels to other risk tools improves breast cancer risk stratification and adds discriminatory benefit on a population basis.In total, 10,025 of 57,902 women aged 46 to 73 years in the Predicting Risk of Cancer at Screening study provided DNA samples. A case-control study was used to evaluate breast cancer risk assessment using polygenic risk scores (PRSs), cancer gene panel (n = 33), mammographic density (density residual [DR]), and risk factors collected using a self-completed 2-page questionnaire (Tyrer-Cuzick [TC] model version 8). In total, 525 cases and 1410 controls underwent gene panel testing and PRS calculation (18, 143, and/or 313 single-nucleotide polymorphisms [SNPs]).Actionable pathogenic variants (PGVs) in BRCA1/2 were found in 1.7% of cases and 0.55% of controls, and overall PGVs were found in 6.1% of cases and 1.3% of controls. A combined assessment of TC8-DR-SNP313 and gene panel provided the best risk stratification with 26.1% of controls and 9.7% of cases identified at1.4% 10-year risk and 9.01% of controls and 23.3% of cases at ≥8% 10-year risk. Because actionable PGVs were uncommon, discrimination was identical with/without gene panel (with/without: area under the curve = 0.67, 95% CI = 0.64-0.70). Only 7 of 17 PGVs in cases resulted in actionable risk category change. Extended case (n = 644)-control (n = 1779) series with TC8-DR-SNP143 identified 18.9% of controls and only 6.4% of stage 2+ cases at1.4% 10-year risk and 20.7% of controls and 47.9% of stage 2+ cases at ≥5% 10-year risk.Further studies and economic analysis will determine whether adding panels to PRS is a cost-effective strategy for risk stratification.

PurposeTo investigate the frequency of germline pathogenic variants (PVs) in women with bilateral breast cancer.MethodsWe undertookBRCA1/2andCHEK2c.1100delC molecular analysis in 764 samples and a multigene panel in 156. Detection rates were assessed by age at first primary, Manchester Score, and breast pathology. Oestrogen receptor (ER) status of the contralateral versus first breast cancer was compared on 1081 patients with breast cancer withBRCA1/BRCA2PVs.Results764 women with bilateral breast cancer have undergone testing ofBRCA1/2andCHEK2; 407 were also tested forPALB2and 177 forATM. Detection rates wereBRCA111.6%,BRCA214.0%,CHEK22.4%,PALB21.0%,ATM1.1% and, for a subset of mainly very early onset tumours,TP534.6% (9 of 195). The highest PV detection rates were for triple negative cancers forBRCA1(26.4%), grade 3 ER+HER2 forBRCA2(27.9%) and HER2+ forCHEK2(8.9%). ER status of the first primary inBRCA1andBRCA2PV heterozygotes was strongly predictive of the ER status of the second contralateral tumour since ~90% of second tumours were ER− inBRCA1heterozygotes, and 50% were ER− inBRCA2heterozygotes if the first was ER−.ConclusionWe have shown a high rate of detection ofBRCA1andBRCA2PVs in triple negative and grade 3 ER+HER2− first primary diagnoses, respectively. High rates of HER2+ were associated withCHEK2PVs, and women ≤30 years were associated withTP53PVs. First primary ER status inBRCA1/2strongly predicts the second tumour will be the same ER status even if unusual for PVs in that gene.

Background Bilateral-Risk-Reducing-Mastectomy-(BRRM) is well described in BRCA1/2 pathogenic variant carriers. However, little is known about the relative uptake, time trends or factors influencing uptake in those at increased breast cancer risk not known to be carriers. The aim of this study is to assess these factors in both groups. Methods BRRM uptake was assessed from entry to the Manchester Family History Clinic or from date of personal BRCA1/2 test. Follow up was censored at BRRM, breast cancer diagnosis, death or January 01, 2020. Cumulative incidence and cause specific and competing risk regression analyses were used to assess the significance of factors associated with BRRM. Results Of 7195 women at ≥25% lifetime breast cancer risk followed for up to 32 years, 451 (6.2%) underwent pre-symptomatic BRRM. Of those eligible in different risk groups the 20-year uptake of BRRM was 47.7%-(95%CI = 42.4–53.2%) in 479 BRCA1/2 carriers; 9.0% (95%CI = 7.26–11.24%) in 1261 women at ≥40% lifetime risk (non-BRCA), 4.8%-(95%CI = 3.98–5.73%) in 3561 women at 30–39% risk and 2.9%-(95%CI = 2.09–4.09%) in 1783 women at 25–29% lifetime risk. In cause-specific Cox regression analysis death of a sister with breast cancer50; OR = 0.26,95%CI = 0.17–0.41). Uptake continued to rise to 20 years from initial risk assessment. Conclusion We have identified several additional factors that correlate with BRRM uptake and demonstrate continued increases over time. These factors will help to tailor counselling and support for women., Highlights • BRRM continues even 20 years post original breast cancer risk assessment. • Potential triggers include death of mother/sister, children and a breast biopsy. • Uptake is clearly informed by lifetime risk of BC and higher in younger the women.

PurposeTo investigate frequency of germline pathogenic variants (PVs) in women with ductal carcinoma in situ (DCIS) and grade 1 invasive breast cancer (G1BC).MethodsWe undertookBRCA1/2analysis in 311 women with DCIS and 392 with G1BC and extended panel testing (non-BRCA1/2) in 176/311 with DCIS and 156/392 with G1BC. We investigated PV detection by age at diagnosis, Manchester Score (MS), DCIS grade and receptor status.Results30/311 (9.6%) with DCIS and 16/392 with G1BC (4.1%) had aBRCA1/2PV (p=0.003), and 24/176-(13.6%) and 7/156-(4.5%), respectively, a non-BRCA1/2PV (p=0.004). Increasing MS was associated with increased likelihood ofBRCA1/2PV in both DCIS and G1BC, although the 10% threshold was not predictive for G1GB. 13/32 (40.6%) DCIS and 0/17 with G1BC BRCA1/2) and 9/90 (non-BRCA1/2), and 8/47 (BRCA1/2) and 8/45 (non-BRCA1/2), respectively. 6/9BRCA1and 3/26BRCA2-associated DCIS were oestrogen receptor negative-(p=0.003). G1BC population testing showed no increased PV rate (OR=1.16, 95% CI 0.28 to 4.80).ConclusionDCIS is more likely to be associated with bothBRCA1/2and non-BRCA1/2PVs than G1BC. Extended panel testing ought to be offered in young-onset DCIS where PV detection rates are highest.

Polygenic risk scores (PRS) for disease risk stratification show great promise for application in general populations, but most are based on data from individuals of white European origin. We assessed two well validated PRS (SNP18, SNP143) in the Predicting-Risk-of-Cancer-At-Screening (PROCAS) study in North-West England for breast cancer prediction based on ethnicity. Overall, 9475 women without breast cancer at study entry, including 645 who subsequently developed invasive breast cancer or ductal carcinoma in situ provided DNA. All were genotyped for SNP18 and a subset of 1868 controls were genotyped for SNP143. For white Europeans both PRS discriminated well between individuals with and without cancer. For n=395 Black (n=112), Asian (n=119), mixed (n=44) or Jewish (n=120) women without cancer both PRS overestimated breast cancer risk, being most marked for women of Black and Jewish origin (p

Background Obesity in early adulthood is associated with lower breast cancer rates in later life. This could be interpreted as a positive reinforcement of excess weight amongst younger women however, the wider implications of higher weights are less well known. This study examined the association between both obesity in early adulthood and body mass index (BMI) change through adulthood, and all-cause mortality. Methods The Predicting Risk of Cancer At Screening (PROCAS) study recruited 57,902 women aged 46–73 years (median age 57.2, IQR 51.8–63.7 years) from the Greater Manchester National Health Service breast screening programme in North West England between 2009 and 2015. It was used to assess associations between BMI at 20 years and cohort entry with all-cause mortality ascertained via deaths recorded on the National Breast Screening System to June 2020. Hazard ratios were estimated using proportional hazards (Cox) regression adjusted for factors at entry to the cohort: age, deprivation, bilateral oophorectomy, hormone-replacement therapy, menopausal status, ethnicity, alcohol intake, physical activity, and BMI. Results The prevalence of overweight (25–30 kg/m2) and obesity (> 30 kg/m2) were 10.4% and 2.5% respectively at 20 years, increasing to 35.2% and 25.9% respectively at cohort entry. After a mean 8.7 years follow-up we observed that overweight (HR = 1.27, 95%CI = 1.10–1.47) and obesity (HR = 2.11, 95%CI = 1.67–2.66) at 20 years had a higher mortality rate compared with healthy weight. Women who were underweight/healthy weight at 20 years and gained weight to obesity at entry had a slightly increased mortality rate compared with women who were underweight/healthy weight at both time points (HR 1.16, 95%CI = 1.02–1.32). Women with overweight (HR = 1.36, 95%CI = 1.06–1.75) or obesity (HR = 1.90, 95%CI = 1.45–2.48) at both 20 years and entry had a higher mortality rate than women who were underweight/healthy weight at both points. Conclusions Women who self-reported overweight and obesity at 20 years had a shorter life expectancy in this cohort of women attending breast cancer screening. Weight gain from 20 years was common in this group. Girls and women should be supported to maintain a healthy weight throughout the lifespan to help increase life expectancy. Trial registration number NCT04359420, retrospectively registered 24/04/2020.

Background: Predict Breast (www.predict.nhs.uk) is an online prognostication and treatment benefit tool for early invasive breast cancer. The aim of this study was to incorporate the prognostic effect of progesterone receptor (PR) status into a new version of PREDICT and to compare its performance to the current version (2.2).Method: The prognostic effect of PR status was based on the analysis of data from 45,088 European patients with breast cancer from 49 studies in the Breast Cancer Association Consortium. Cox proportional hazard models were used to estimate the hazard ratio for PR status. Data from a New Zealand study of 11,365 patients with early invasive breast cancer were used for external validation. Model calibration and discrimination were used to test the model performance.Results: Having a PR-positive tumour was associated with a 23% and 28% lower risk of dying from breast cancer for women with oestrogen receptor (ER)-negative and ER-positive breast cancer, respectively. The area under the ROC curve increased with the addition of PR status from 0.807 to 0.809 for patients with ER-negative tumours (p = 0.023) and from 0.898 to 0. 902 for patients with ER-positive tumours (p = 2.3 x 10(-6)) in the New Zealand cohort. Model calibration was modest with 940 observed deaths compared to 1151 predicted.Conclusion: The inclusion of the prognostic effect of PR status to PREDICT Breast has led to an improvement of model performance and more accurate absolute treatment benefit predic-tions for individual patients. Further studies should determine whether the baseline hazard function requires recalibration. (C) 2022 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

PURPOSE To investigate the contribution of PALB2 pathogenic gene variants (PGVs, PALB2_PGV) and the CHEK2 c.1100delC (CHEK2_1100delC) PGV to familial breast and ovarian cancer, and PALB2_PGV associated breast cancer pathology. METHODS Outcomes of germline PALB2_PGV and CHEK2_1100delC testing were recorded in 3,127 women with histologically confirmed diagnoses of invasive breast cancer, carcinoma in situ, or epithelial nonmucinous ovarian cancer, and 1,567 female controls. Breast cancer pathology was recorded in PALB2_PGV cases from extended families. RESULTS Thirty-five PALB2 and 44 CHEK2_1100delC PGVs were detected in patients (odds ratio [OR] PALB2 breast-ovarian = 5.90 [95% CI: 1.92-18.36], CHEK2 breast-ovarian = 4.46 [95% CI: 1.86-10.46], PALB2 breast = 6.16 [95% CI: 1.98-19.21], CHEK2 breast = 4.89 [95% CI: 2.01-11.34]). Grade 3 ER-positive HER2-negative, grade 3 and triple negative (TN) tumors were enriched in cases with PALB2 PGVs compared with all breast cancers known to our service (respectively: 15/43, 254/1,843, P = 0.0005; 28/37, 562/1,381, P = 0.0001; 12/43, 204/1,639, P

Background Follicular lymphoma (FL) prognosis is influenced by the composition of the tumour microenvironment. We tested an automated approach to quantitatively assess the phenotypic and spatial immune infiltrate diversity as a prognostic biomarker for FL patients. Methods Diagnostic biopsies were collected from 127 FL patients initially treated with rituximab-based therapy (52%), radiotherapy (28%), or active surveillance (20%). Tissue microarrays were constructed and stained using multiplex immunofluorescence (CD4, CD8, FOXP3, CD21, PD-1, CD68, and DAPI). Subsequently, sections underwent automated cell scoring and analysis of spatial interactions, defined as cells co-occurring within 30 μm. Shannon’s entropy, a metric describing species biodiversity in ecological habitats, was applied to quantify immune infiltrate diversity of cell types and spatial interactions. Immune infiltrate diversity indices were tested in multivariable Cox regression and Kaplan–Meier analysis for overall (OS) and progression-free survival (PFS). Results Increased diversity of cell types (HR = 0.19 95% CI 0.06–0.65, p = 0.008) and cell spatial interactions (HR = 0.39, 95% CI 0.20–0.75, p = 0.005) was associated with favourable OS, independent of the Follicular Lymphoma International Prognostic Index. In the rituximab-treated subset, the favourable trend between diversity and PFS did not reach statistical significance. Conclusion Multiplex immunofluorescence and Shannon’s entropy can objectively quantify immune infiltrate diversity and generate prognostic information in FL. This automated approach warrants validation in additional FL cohorts, and its applicability as a pre-treatment biomarker to identify high-risk patients should be further explored. The multiplex image dataset generated by this study is shared publicly to encourage further research on the FL microenvironment.

BackgroundWhile the likelihood of identifying constitutional breast cancer-associated BRCA1, BRCA2 and TP53 pathogenic variants (PVs) increases with earlier diagnosis age, little is known about the correlation with age at diagnosis in other predisposition genes. Here, we assessed the contribution of known breast cancer-associated genes to very early onset disease.MethodsSequencing of BRCA1, BRCA2, TP53 and CHEK2 c.1100delC was undertaken in women with breast cancer diagnosed ≤30 years. Those testing negative were screened for PVs in a minimum of eight additional breast cancer-associated genes. Rates of PVs were compared with cases ≤30 years from the Prospective study of Outcomes in Sporadic vs Hereditary breast cancer (POSH) study.ResultsTesting 379 women with breast cancer aged ≤30 years identified 75 PVs (19.7%) in BRCA1, 35 (9.2%) in BRCA2, 22 (5.8%) in TP53 and 2 (0.5%) CHEK2 c.1100delC. Extended screening of 184 PV negative women only identified eight additional actionable PVs. BRCA1/2 PVs were more common in women aged 26–30 years than in younger women (p=0.0083) although the younger age group had rates more similar to those in the POSH cohort. Out of 26 women with ductal carcinoma in situ (DCIS) alone, most were high-grade and 11/26 (42.3%) had a PV (TP53=6, BRCA2=2, BRCA1=2, PALB2=1). This PV yield is similar to the 61 (48.8%) BRCA1/2 PVs identified in 125 women with triple-negative breast cancer. The POSH cohort specifically excluded pure DCIS which may explain lower TP53 PV rates in this group (1.7%).ConclusionThe rates of BRCA1, BRCA2 and TP53 PVs are high in very early onset breast cancer, with limited benefit from testing of additional breast cancer-associated genes.

BackgroundWomen testing positive for BRCA1/2 pathogenic variants have high lifetime risks of breast cancer (BC) and ovarian cancer. The effectiveness of risk reducing surgery (RRS) has been demonstrated in numerous previous studies. We evaluated long-term uptake, timing and effectiveness of risk reducing mastectomy (RRM) and bilateral salpingo-oophorectomy (RRSO) in healthy BRCA1/2 carriers.MethodsWomen were prospectively followed up from positive genetic test (GT) result to censor date. χ² testing compared categorical variables; Cox regression model estimated HRs and 95% CI for BC/ovarian cancer cases associated with RRS, and impact on all-cause mortality; Kaplan-Meier curves estimated cumulative RRS uptake. The annual cancer incidence was estimated by women-years at risk.ResultsIn total, 887 women were included in this analysis. Mean follow-up was 6.26 years (range=0.01–24.3; total=4685.4 women-years). RRS was performed in 512 women, 73 before GT. Overall RRM uptake was 57.9% and RRSO uptake was 78.6%. The median time from GT to RRM was 18.4 months, and from GT to RRSO–10.0 months. Annual BC incidence in the study population was 1.28%. Relative BC risk reduction (RRM versus non-RRM) was 94%. Risk reduction of ovarian cancer (RRSO versus non-RRSO) was 100%.ConclusionOver a 24-year period, we observed an increasing number of women opting for RRS. We showed that the timing of RRS remains suboptimal, especially in women undergoing RRSO. Both RRM and RRSO showed a significant effect on relevant cancer risk reduction. However, there was no statistically significant RRSO protective effect on BC.

Risk-reducing bilateral salpingo-oophorectomy (RRBSO) is highly effective for the prevention of high-grade serous ovarian cancer (HGSOC) in BRCA1/2 pathogenic variant carriers (PVCs), but does not completely eliminate future risk of primary peritoneal cancer (PPC). The requirement to completely remove fallopian tubes at RRBSO and carefully exclude occult cancer/serous tubal intraepithelial carcinoma (STIC) lesions may not have been appreciated historically. We calculated rates of HGSOC and PPC in confirmed BRCA1/2 PVCs registered on the regional database in those who did (cases) and did not (controls) undergo RRBSO after genetic testing. Expected annual rates of ovarian/peritoneal cancer were 1% for BRCA1 ≥ 35 years and 0.5% for BRCA2 ≥ 45 years. Follow-up before 35/45 years was "risk free" and lead time excluded RRBSO

Objective This study aims to establish risk of breast cancer based on breast density among Saudi women and to compare cancer prediction using different breast density methods. Methods 1140 pseudonymised screening mammograms from Saudi females were retrospectively collected. Breast density was assessed using Breast Imaging Reporting and Data System (BI-RADS) density categories and visual analogue scale (VAS) of 285 cases and 855 controls matched on age and body mass index. In a subset of 160 cases and 480 controls density was estimated by two automated methods, Volpara Density™ and predicted VAS (pVAS). Odds ratios (ORs) between the highest and second categories in BI-RADS and Volpara density grades, and highest vs lowest quartiles in VAS, pVAS and Volpara Density™, were estimated using conditional logistic regression. Results: For BI-RADS, the OR was 6.69 (95% CI 2.79–16.06) in the highest vs second category and OR = 4.78 (95% CI 3.01–7.58) in the highest vs lowest quartile for VAS. In the subset, VAS was the strongest predictor OR = 7.54 (95% CI 3.86–14.74), followed by pVAS using raw images OR = 5.38 (95% CI 2.68–10.77) and Volpara Density ™ OR = 3.55, (95% CI 1.86–6.75) for highest vs lowest quartiles. The matched concordance index for VAS was 0.70 (95% CI 0.65–0.75) demonstrating better discrimination between cases and controls than all other methods. Conclusion Increased mammographic density was strongly associated with risk of breast cancer among Saudi women. Radiologists’ visual assessment of breast density is superior to automated methods. However, pVAS and Volpara Density ™ also significantly predicted breast cancer risk based on breast density. Advances in knowledge Our study established an association between breast density and breast cancer in a Saudi population and compared the performance of automated methods. This provides a stepping-stone towards personalised screening using automated breast density methods.

Poly(ADP-ribose) polymerase (PARP) inhibitors improve survival in BRCA-mutant high-grade serous ovarian carcinoma. As a result, germline and somatic BRCA1/2 testing has become standard practice in women diagnosed with ovarian cancer. We outline changes in testing and detection rates of germline BRCA1/2 pathogenic variants (PVs) in cases of non-mucinous epithelial ovarian cancer diagnosed during three eras, spanning 12 years, within the North West of England, and compare the uptake of cascade testing in families identified by oncology-led mainstreaming versus regional genetics clinics. Eras included: Period 1 (20% risk threshold for testing): between January 2007 and May 2013; Period 2 (10% risk threshold for testing): between June 2013 and October 2017 and; Period 3 (mainstream testing): between November 2017 and November 2019. A total of 1081 women underwent germline BRCA1/2 testing between January 2007 and November 2019 and 222 (20.5%) were found to have a PV. The monthly testing rate increased by 3.3-fold and 2.5-fold between Periods 1–2 and Periods 2–3, respectively. A similar incidence of germline BRCA1/2 PVs were detected in Period 2 (17.2%) and Period 3 (18.5%). Uptake of cascade testing from first-degree relatives was significantly lower in those women undergoing mainstream testing compared with those tested in regional genetics clinics (31.6% versus 47.3%, P = 0.038). Mainstream testing allows timely detection of germline BRCA1/2 status to select patients for PARP inhibitors, but shortfalls in the uptake of cascade testing in first-degree relatives requires optimisation to broaden benefits within families.

The incidence of breast cancer continues to increase worldwide. Population-based screening is available in many countries but may not be the most efficient use of resources, thus interest in risk-based/stratified screening has grown significantly in recent years. An important part of risk-based screening is the incorporation of mammographic density (MD) and single nucleotide polymorphisms (SNPs) into risk prediction models to be combined with classical risk factors. In this article, we discuss different measures of MD and risk prediction models that are available. Risk-stratified screening options including supplemental or alternative screening modalities including digital breast tomosynthesis (DBT), automated ultrasound (ABUS) and magnetic resonance imaging (MRI) are discussed, as well as potential risk-based interventions (diet and lifestyle, chemoprevention and risk-reducing surgery). Furthermore, we look at risk feedback in practice and the cost-effectiveness and acceptability of risk-based screening, highlighting some of the current challenges.

BackgroundGenetic testing for BRCA1 and BRCA2 pathogenic variants (PVs) has been available in North West England since 1995. We assessed uptake of pre-symptomatic testing in 1564 families with PVs over a 24.5year follow-up (FU) period.MethodsFirst-degree relatives (FDRs) in families with BRCA1 or BRCA2 PVs were eligible from date of index family report if unaffected by a relevant cancer and alive at report date. FDRs were censored as not having undergone a pre-symptomatic test at diagnosis of a relevant cancer, date of death, age 93 or 30/03/2019. Time to uptake of pre-symptomatic testing was assessed by Kaplan–Meier curves, by gender and children.Results2554 male and 3115 female FDRs were eligible. Overall uptake was 775 (30.3%) in men and 1935 (62.1%) in women. This increased at 15 years to 33.6% and 67.9%, and continued to rise until 24 years (p80% by 15 years. Uptake was higher in parous women (pConclusionUptake of BRCA1/2 pre-symptomatic testing is age, gender and time-dependent, and higher in women with children and men with daughters.

Genome-wide analysis identifies 32 loci associated with breast cancer susceptibility, accounting for estrogen receptor, progesterone receptor and human epidermal growth factor receptor 2 status and tumor grade. Breast cancer susceptibility variants frequently show heterogeneity in associations by tumor subtype(1-3). To identify novel loci, we performed a genome-wide association study including 133,384 breast cancer cases and 113,789 controls, plus 18,908 BRCA1 mutation carriers (9,414 with breast cancer) of European ancestry, using both standard and novel methodologies that account for underlying tumor heterogeneity by estrogen receptor, progesterone receptor and human epidermal growth factor receptor 2 status and tumor grade. We identified 32 novel susceptibility loci (P < 5.0 x 10(-8)), 15 of which showed evidence for associations with at least one tumor feature (false discovery rate < 0.05). Five loci showed associations (P < 0.05) in opposite directions between luminal and non-luminal subtypes. In silico analyses showed that these five loci contained cell-specific enhancers that differed between normal luminal and basal mammary cells. The genetic correlations between five intrinsic-like subtypes ranged from 0.35 to 0.80. The proportion of genome-wide chip heritability explained by all known susceptibility loci was 54.2% for luminal A-like disease and 37.6% for triple-negative disease. The odds ratios of polygenic risk scores, which included 330 variants, for the highest 1% of quantiles compared with middle quantiles were 5.63 and 3.02 for luminal A-like and triple-negative disease, respectively. These findings provide an improved understanding of genetic predisposition to breast cancer subtypes and will inform the development of subtype-specific polygenic risk scores.