BackgroundHeterogeneity of immune gene expression patterns of luminal breast cancer (BC), which is clinically heterogeneous and overall considered as low immunogenic, has not been well studied especially in non-European populations. Here, we aimed at characterizing the immune gene expression profile of luminal BC in an Asian population and associating it with patient characteristics and tumor genomic features.MethodsWe performed immune gene expression profiling of tumor and adjacent normal tissue in 92 luminal BC patients from Hong Kong using RNA-sequencing data and used unsupervised consensus clustering to stratify tumors. We then used luminal patients from The Cancer Genome Atlas (TCGA, N = 564) and a Korean breast cancer study (KBC, N = 112) as replication datasets.ResultsBased on the expression of 130 immune-related genes, luminal tumors were stratified into three distinct immune subtypes. Tumors in one subtype showed higher level of tumor-infiltrating lymphocytes (TILs), characterized by T cell gene activation, higher expression of immune checkpoint genes, higher nonsynonymous mutation burden, and higher APOBEC-signature mutations, compared with other luminal tumors. The high-TIL subtype was also associated with lower ESR1/ESR2 expression ratio and increasing body mass index. The comparison of the immune profile in tumor and matched normal tissue suggested a tumor-derived activation of specific immune responses, which was only seen in high-TIL patients. Tumors in a second subtype were characterized by increased expression of interferon-stimulated genes and enrichment for TP53 somatic mutations. The presence of three immune subtypes within luminal BC was replicated in TCGA and KBC, although the pattern was more similar in Asian populations. The germline APOBEC3B deletion polymorphism, which is prevalent in East Asian populations and was previously linked to immune activation, was not associated with immune subtypes in our study. This result does not support the hypothesis that the germline APOBEC3B deletion polymorphism is the driving force for immune activation in breast tumors in Asian populations.ConclusionOur findings suggest that immune gene expression and associated genomic features could be useful to further stratify luminal BC beyond the current luminal A/B classification and a subset of luminal BC patients may benefit from checkpoint immunotherapy, at least in Asian populations.

Purpose-Mammographic density (MD) is a strong risk factor for breast cancer, yet its relationship with tumor characteristics is not well established, particularly in Asian populations.Methods-MD was assessed from a total of 2001 Chinese breast cancer patients using Breast Imaging Reporting and Data System (BI-RADS) categories. Molecular subtypes were defined using immunohistochemical status on ER, PR, HER2, and Ki-67, as well as tumor grade. Multinomial logistic regression was used to test associations between MD and molecular subtype (luminal A = reference) adjusting for age, body mass index (BMI), menopausal status, parity, and nodal status.Results-The mean age at diagnosis was 51.7 years (SD = 10.7) and the average BMI was 24.7 kg/m 2 (SD = 3.8). The distribution of BI-RADS categories was 7.4% A = almost entirely fat, 24.2% B = scattered fibroglandular dense, 49.4% C = heterogeneously dense, and 19.0% D = extremely dense. Compared to women with BI-RADS = A/B, women with BI-RADS = D were more likely to have HER2-enriched tumors (OR = 1.81, 95% CI 1.08-3.06, p = 0.03), regardless of menopausal status. The association was only observed in women with normal (< 25 kg/m 2 ) BMI (OR = 2.43, 95% CI 1.24-4.76, p < 0.01), but not among overweight/obese women (OR: 0.98, 95% CI 0.38-2.52, p = 0.96).

Disease heterogeneity of immune gene expression patterns of luminal breast cancer (BC) has not been well studied. We performed immune gene expression profiling of tumor and adjacent normal tissue in 92 Asian luminal BC patients and identified three distinct immune subtypes. Tumors in one subtype exhibited signs of T-cell activation, lower ESR1/ESR2 expression ratio and higher expression of immune checkpoint genes, nonsynonymous mutation burden, APOBEC-signature mutations, and increasing body mass index compared to other luminal tumors. Tumors in a second subtype were characterized by increased expression of interferonstimulated genes and enrichment for TP53 somatic mutations. The presence of three immune subtypes within luminal BC was replicated in cases drawn from The Cancer Genome Atlas and a Korean breast cancer study. Our findings suggest that immune gene expression and associated genomic features could be useful to further stratify luminal BC beyond the current luminal A/B classification.Introduction:

e22226 Background: Breast cancers due to underlying germline BRCA1 and BRCA2 mutations are associated with particular pathological features that may differ from sporadic breast cancers. We report clinical and pathologic characteristics of breast cancer in a clinical cohort of high risk Chinese women with BRCA mutations and those without mutations. Methods: 202 high risk women based on their age and family history were recruited from March 2007 to November 2008. Medical information was prospectively collected from the patients and medical records. BRCA1 and BRCA2 mutations were detected using full gene sequencing and multiplex ligation-dependent probe amplification (MLPA). Results: Of the 202 female probands tested, 25 (12.3 %) were BRCA mutation carriers of which 11 (44%) were BRCA1 and 14 (56%) were BRCA2 mutations. Breast cancer risk factors, other than family history, did not differ between carriers and non-carriers. Mutation carriers were more likely to have a familial history of breast cancer (p=0.07) and personal and family history of ovarian cancer (p=0.005; p=0.007). Other cancers found in carriers families included pancreatic, gastric, colon, lung, liver, and nasopharyngeal. 23% of women diagnosed with DCIS had BRCA mutations compared with 11.4% of those with invasive cancers. BRCA related tumors were more likely to be ER, PR and Her-2 negative (Triple negative, TN) (p= 0.006). Overall 9.6% of non-BRCA cancers were TN whereas 25.9% of BRCA cancers were TN. Prevalence of TN in BRCA1 carriers is 71% compared with 13.4% in BRCA2 carriers. BRCA1 mutation related cancers were significantly more likely to be ER negative than BRCA2 and this is only significant in those who are under 40 years of age (p=0.070). Conclusions: We have a high BRCA2 mutation rate in our cohort. BRCA related breast cancer is associated with families with increasing number of first degree relatives with breast and/or ovarian cancers and were higher for DCIS cancers. Prevalence of TN breast cancers was high compared to Caucasian cohorts. BRCA mutations were associated with pathologically, poor prognostic features (TN and high grade) especially in younger women. No significant financial relationships to disclose.