Breast Cancer Molecular Subtypes Among Moroccan Women

Introduction: Breast cancer remains despite the therapeutic progress, the leading cause of death by cancer among women. It represents a group of very heterogeneous clinical, histopathological and molecular diseases. Molecular heterogeneity has been demonstrated by genomic analysis, even for similar histology cancers. Four subgroups of breast carcinomas are distinguished: Luminal A, Luminal B, HER2 over expression and Basal - like. The Immuno-histo-chemical analysis useip (estrogen receptors) RE, the PR (progesterone receptors), the ((Human Epidermal Growth Factor Receptor-2), the Ki67 (proliferation marker) HER2, CK5/6) has shown a subdivision into subgroups similar to those found by genomic analysis. These subgroups are different from the point of view of clinical course and response to adjuvant treatment. Objectives: The aim of this work is to study the molecular profile of the breast cancers by immunostaining on Moroccan series to a classification with a prognostic value allowing a treatment tailored to each group of patients. Furthermore, the molecular subgroups were correlated to other clinical and histological factors. Material and methods: It is a prospective study of the laboratory of Anatomy and Pathologic cytology of the children's Hospital, the service I of the maternity hospital in Rabat and in cooperation with the United Nations Centre of pathological anatomy. To do this, 88 cases of breast cancer together were diagnosed between January 1, 2010 and December 31, 2014, taking a period of five years. All tissue samples made subject study of Immuno-histo-chemistry with the following markers: RE, PR, HER2 and Ki67. Only negative triple cases (HR and HER2 negative) benefited from an additional marking with CK5/6 and EGFR to set the basal profile. Results: Series of 88 cases of mammary carcinomas observed on operating parts, ranged in age between 28 and 84 years old, with an average of 51 ± 12, 8. Carcinoma infiltrating non-specific (DOCTORS) was the most frequent (87.5%). Ranks histo-prognostic Scarff Bloom and Richardson (SBR) 2 and 3 respectively accounted for 45.5 and 51.1% of cases and only 2, 3% of the DOCTORS were grade 1. The Luminal B (53.4%) was under the most common molecular group, followed by Luminal A (23.9%), HER2 + (15.9%) and triple negative (6.8%). The correlation of molecular type of tumors with different prognostic factors showed only one significant connection with the SBR grade.

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ER, PR, HER2, Ki-67 and CK5 in Early and Late Relapsing Breast Cancer—Reduced CK5 Expression in Metastases

Breast Cancer Basic and Clinical Research ◽

10.4137/bcbcr.s10701 ◽

2013 ◽

Vol 7 ◽

pp. BCBCR.S10701 ◽

Cited By ~ 10

Author(s):

Kristiina Joensuu ◽

Marjut Leidenius ◽

Mia Kero ◽

Leif C. Andersson ◽

Kathryn B. Horwitz ◽

...

Keyword(s):

Breast Cancer ◽

Cancer Progression ◽

Triple Negative ◽

Significant Risk ◽

Growth Factor Receptor ◽

Primary Therapy ◽

Breast Cancers ◽

Luminal A ◽

Ki 67 ◽

Luminal B

Breast cancer can recur even decades after the primary therapy. Markers are needed to predict cancer progression and the risk of late recurrence. The estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor-2 (HER2), proliferation marker Ki-67, and cytokeratin CK5 were studied to find out whether their expression or occurrence in subgroups of breast cancers correlated with the time of recurrence. The expression of HER2, ER, PR, Ki-67, and CK5 was studied by IHC in 72 primary breast cancers and their corresponding recurrent/metastatic lesions. The patients were divided into three groups according to the time of the recurrence/metastasis: before two years, after 5 years, and after 10 years. Based on their IHC profiles, the tumors were divided into surrogates of the genetically defined subgroups of breast cancers and the subtype definitions were as follows: luminal A (ER or PR+HER2–), luminal B (ER or PR+HER2+), HER2 overexpressing (ER–PR–HER2+), triple-negative (ER–PR–HER2–), basal-like (ER–PR–HER2–CK5+), non-classified (ER–PR–HER2–CK5–) and luminobasal (ER or PR+CK5+). In multivariate analysis, tumor size and HER2 positivity were a significant risk of early cancer relapse. The metastases showed a significantly lower CK5 expression. CK5 positivity distinguished triple negative tumors into rapidly and slowly recurring cancers. The IHC subtype ER or PR+HER2– luminal A presented a significantly lower risk of early tumor recurrence. Ki-67 expression denoted early-relapsing tumors and correlated linearly with tumor progression, since Ki-67 positivity declined gradually from early-relapsing toward late-recurring cancers.

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Evaluation of FGFR targeting in breast cancer through interrogation of patient-derived models

Breast Cancer Research ◽

10.1186/s13058-021-01461-4 ◽

2021 ◽

Vol 23 (1) ◽

Author(s):

Nicole J. Chew ◽

Terry C. C. Lim Kam Sian ◽

Elizabeth V. Nguyen ◽

Sung-Young Shin ◽

Jessica Yang ◽

...

Keyword(s):

Breast Cancer ◽

Therapeutic Target ◽

Breast Cancer Subtype ◽

Breast Cancer Subtypes ◽

Cancer Tissue ◽

Breast Cancers ◽

Luminal A ◽

Tissue Samples ◽

Cancer Subtypes ◽

Luminal B

Abstract Background Particular breast cancer subtypes pose a clinical challenge due to limited targeted therapeutic options and/or poor responses to the existing targeted therapies. While cell lines provide useful pre-clinical models, patient-derived xenografts (PDX) and organoids (PDO) provide significant advantages, including maintenance of genetic and phenotypic heterogeneity, 3D architecture and for PDX, tumor–stroma interactions. In this study, we applied an integrated multi-omic approach across panels of breast cancer PDXs and PDOs in order to identify candidate therapeutic targets, with a major focus on specific FGFRs. Methods MS-based phosphoproteomics, RNAseq, WES and Western blotting were used to characterize aberrantly activated protein kinases and effects of specific FGFR inhibitors. PDX and PDO were treated with the selective tyrosine kinase inhibitors AZD4547 (FGFR1-3) and BLU9931 (FGFR4). FGFR4 expression in cancer tissue samples and PDOs was assessed by immunohistochemistry. METABRIC and TCGA datasets were interrogated to identify specific FGFR alterations and their association with breast cancer subtype and patient survival. Results Phosphoproteomic profiling across 18 triple-negative breast cancers (TNBC) and 1 luminal B PDX revealed considerable heterogeneity in kinase activation, but 1/3 of PDX exhibited enhanced phosphorylation of FGFR1, FGFR2 or FGFR4. One TNBC PDX with high FGFR2 activation was exquisitely sensitive to AZD4547. Integrated ‘omic analysis revealed a novel FGFR2-SKI fusion that comprised the majority of FGFR2 joined to the C-terminal region of SKI containing the coiled-coil domains. High FGFR4 phosphorylation characterized a luminal B PDX model and treatment with BLU9931 significantly decreased tumor growth. Phosphoproteomic and transcriptomic analyses confirmed on-target action of the two anti-FGFR drugs and also revealed novel effects on the spliceosome, metabolism and extracellular matrix (AZD4547) and RIG-I-like and NOD-like receptor signaling (BLU9931). Interrogation of public datasets revealed FGFR2 amplification, fusion or mutation in TNBC and other breast cancer subtypes, while FGFR4 overexpression and amplification occurred in all breast cancer subtypes and were associated with poor prognosis. Characterization of a PDO panel identified a luminal A PDO with high FGFR4 expression that was sensitive to BLU9931 treatment, further highlighting FGFR4 as a potential therapeutic target. Conclusions This work highlights how patient-derived models of human breast cancer provide powerful platforms for therapeutic target identification and analysis of drug action, and also the potential of specific FGFRs, including FGFR4, as targets for precision treatment.

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Subtypes of Breast Cancer in Northern India- An Immunohistomolecular Subtypes of Invasive Breast Cancer

JOURNAL FOR CLINICAL AND DIAGNOSTIC RESEARCH ◽

10.7860/jcdr/2020/46020.14169 ◽

2020 ◽

Author(s):

Amit Kumar Sinha ◽

Amrita Ghosh

Keyword(s):

Breast Cancer ◽

Therapeutic Response ◽

Molecular Subtype ◽

Growth Factor Receptor ◽

Normal Breast ◽

Breast Cancers ◽

Luminal A ◽

Luminal B ◽

Molecular Subclass ◽

Epidermal Growth

Introduction: Breast cancer is a heterogeneous disease that may differ in therapeutic response and prognosis despite similarities in histopathologic types, grade and stage. Molecular studies have identified distinct subtypes of breast carcinoma each having unique recognisable phenotypes and clinical outcomes. Aim: To study the histomorphological features and Immunohistochemical (IHC) profile of breast cancer, to study the distribution of molecular subclass, and to study the morphological features of different molecular subclasses and to determine the association between the pathological features associated with adverse prognosis with the molecular subclass. Materials and Methods: Present study was a prospective cross-sectional observational study based on mastectomy specimens of 122 cases of consecutive cases of invasive breast cancer submitted from June 2012 to February 2014 in Department of Pathology, Institute of Medical Sciences, Banaras Hindu University, Varanasi, Uttar Pradesh, India. On IHC staining with Estrogen Receptors (ER), Progesterone Receptors (PR), Human Epidermal growth factor Receptor 2 (HER2), Cytokeratin (CK5/6) and Epidermal Growth Factor Receptor (EGFR) these cases were classified into Luminal A, Luminal B, HER2 overexpression, basal like and normal breast like molecular subclass. All statistical analysis were performed using Statistical Package for the Social Sciences (SPSS) version 16 (SPSS, Inc., Chicago, IL, USA). Results: The proportion of each subytpes detected in present study were: Luminal A-28.69% (35), Luminal B-17.21% (21), HER2 over expressing-25.41% (31), Basal Like Breast Carcinoma (BLBC)-26.23% (32) and the rest unclassified category (normal breast like)-2.46% (3). The following variables were significantly associated with molecular breast cancer subtypes. The tumours of BLBC and HER2 overexpressing were larger, poorly differentiated, higher mitotic index, more number of positive lymph nodes and with more geographic and central necrosis than Luminal A group. These features were statistically significant (p<0.05). Conclusion: Identification of molecular subtype of breast cancer is extremely important for predicting prognosis and therapeutic response of the breast cancers and thus has role in management of patients of breast cancers. BLBC is a molecular subtype of breast cancer known for its aggressive behaviour and poor prognosis is identified by expression of basal CKs.

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Luminal B Breast Cancer: Molecular Characterization, Clinical Management, and Future Perspectives

Journal of Clinical Oncology ◽

10.1200/jco.2013.54.1870 ◽

2014 ◽

Vol 32 (25) ◽

pp. 2794-2803 ◽

Cited By ~ 140

Author(s):

Felipe Ades ◽

Dimitrios Zardavas ◽

Ivana Bozovic-Spasojevic ◽

Lina Pugliano ◽

Debora Fumagalli ◽

...

Keyword(s):

Breast Cancer ◽

Molecular Characterization ◽

Hormone Receptors ◽

Growth Factor Receptor ◽

Breast Cancers ◽

Luminal A ◽

Proliferation Markers ◽

Ongoing Research ◽

Next Generation Sequencing Technology ◽

Luminal B

Gene expression profiling has reshaped our understanding of breast cancer by defining and characterizing four main intrinsic molecular subtypes: human epidermal growth factor receptor 2–enriched, basal-like, luminal A, and luminal B subtypes. Luminal B breast cancer has been reported to have lower expression of hormone receptors, higher expression of proliferation markers, and higher histologic grade than luminal A. It also exhibits worse prognosis and has a distinct profile of response to hormone therapy and chemotherapy. Although luminal cancers share similarities, the studies conducted in recent years using next-generation sequencing technology show that luminal A and B breast cancers should be perceived as distinct entities, with specific oncogenic drivers, rather than more proliferative varieties of luminal tumors. This review discusses the definition and molecular characterization of luminal B breast cancer and presents the available clinical evidence for chemotherapy and endocrine therapy patterns of response. It also provides an overview of ongoing research on molecularly targeted agents for this disease.

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Is There a Correlation between Multiparametric Assessment in Ultrasound and Intrinsic Subtype of Breast Cancer?

Journal of Clinical Medicine ◽

10.3390/jcm10225394 ◽

2021 ◽

Vol 10 (22) ◽

pp. 5394

Author(s):

Magdalena Gumowska ◽

Joanna Mączewska ◽

Piotr Prostko ◽

Katarzyna Roszkowska-Purska ◽

Katarzyna Dobruch-Sobczak

Keyword(s):

Breast Cancer ◽

Molecular Subtypes ◽

Treatment Strategies ◽

Growth Factor Receptor ◽

Molecular Profile ◽

Her2 Overexpression ◽

Imaging Features ◽

Luminal A ◽

Luminal B ◽

Post Surgery

Molecular profile of breast cancer provides information about its biological activity, prognosis and treatment strategies. The purpose of our study was to investigate the correlation between ultrasound features and molecular subtypes of breast cancer. From June 2019 to December 2019, 86 patients (median age 57 years; range 32–88) with 102 breast cancer tumors were included in the study. The molecular subtypes were classified into five types: luminal A (LA), luminal B without HER2 overexpression (LB HER2−), luminal B with HER2 overexpression (LB HER2+), human epidermal growth factor receptor 2 positive (HER2+) and triple negative breast cancer (TNBC). Histopathological verification was obtained in core biopsy or/and post-surgery specimens in all cases. Univariate logistic regression analysis was performed to assess the association between the subtypes and ultrasound imaging features. Experienced radiologists assessed lesions according to the BIRADS-US lexicon. The ultrasound scans were performed with a Supersonic Aixplorer and Supersonix. Based on histopathological verification, the rates of LA, LB HER2−, LB HER2+, HER2+, and TNBC were 33, 17, 17, 16, 19, respectively. Both LB HER2+ and HER2+ subtypes presented higher incidence of calcification (OR = 3.125, p = 0.02, CI 0.0917–5.87) and HER2+ subtype presented a higher incidence of posterior enhancement (OR = 5.75, p = 0.03, CI 1.2257–32.8005), compared to other subtypes. The calcifications were less common in TNBC (OR = 0.176, p = 0.0041, CI 0.0469–0.5335) compared to other subtypes. There were no differences with regard to margin, shape, orientation, elasticity values and vascularity among five molecular subtypes. Our results suggest that there is a correlation between ultrasonographic features assessed according to BIRADS-US lexicon and BC subtypes with HER2 overexpression (both LB HER2+ and HER2+). It may be useful for identification of these aggressive subtypes of breast cancer.

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Cancer-Associated Fibroblasts in Breast Cancer Treatment Response and Metastasis

Cancers ◽

10.3390/cancers13133146 ◽

2021 ◽

Vol 13 (13) ◽

pp. 3146

Author(s):

Patricia Fernández-Nogueira ◽

Gemma Fuster ◽

Álvaro Gutierrez-Uzquiza ◽

Pere Gascón ◽

Neus Carbó ◽

...

Keyword(s):

Breast Cancer ◽

Hormone Receptors ◽

Treatment Strategies ◽

Specific Treatment ◽

Growth Factor Receptor ◽

Cancer Associated Fibroblasts ◽

Luminal A ◽

Luminal B ◽

Number Of Patients ◽

Current Therapies

Breast cancer (BrCa) is the leading cause of death among women worldwide, with about one million new cases diagnosed each year. In spite of the improvements in diagnosis, early detection and treatment, there is still a high incidence of mortality and failure to respond to current therapies. With the use of several well-established biomarkers, such as hormone receptors and human epidermal growth factor receptor-2 (HER2), as well as genetic analysis, BrCa patients can be categorized into multiple subgroups: Luminal A, Luminal B, HER2-enriched, and Basal-like, with specific treatment strategies. Although chemotherapy and targeted therapies have greatly improved the survival of patients with BrCa, there is still a large number of patients who relapse or who fail to respond. The role of the tumor microenvironment in BrCa progression is becoming increasingly understood. Cancer-associated fibroblasts (CAFs) are the principal population of stromal cells in breast tumors. In this review, we discuss the current understanding of CAFs’ role in altering the tumor response to therapeutic agents as well as in fostering metastasis in BrCa. In addition, we also review the available CAFs-directed molecular therapies and their potential implications for BrCa management.

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Low KIBRA Expression Is Associated with Poor Prognosis in Patients with Triple-Negative Breast Cancer

Medicina ◽

10.3390/medicina57080837 ◽

2021 ◽

Vol 57 (8) ◽

pp. 837

Author(s):

So-Woon Kim ◽

Jinah Chu ◽

Sung-Im Do ◽

Kiyong Na

Keyword(s):

Breast Cancer ◽

Triple Negative Breast Cancer ◽

Poor Prognosis ◽

Triple Negative ◽

Histological Grade ◽

Growth Factor Receptor ◽

Hippo Signaling ◽

Luminal A ◽

Luminal B ◽

Epidermal Growth

Background and Objectives: Kidney and brain protein (KIBRA) is a protein encoded by the WW and C2 domain containing 1 (WWC1) gene and is involved in the Hippo signaling pathway. Recent studies have revealed the prognostic value of KIBRA expression; however, its role in breast cancer remains unclear. The aim of this study was to examine KIBRA expression in relation to the clinical and pathological characteristics of patients with breast cancer and to disease outcomes. Materials and Methods: We analyzed the expression of KIBRA and its correlation with event-free survival (EFS) outcomes in resected samples from 486 patients with breast cancer. Results: KIBRA expression was significantly different among the molecular subgroups (low KIBRA expression: luminal A, 46.7% versus 50.0%, p = 0.641; luminal B, 32.7% versus 71.7%, p < 0.001; human epidermal growth factor receptor 2 (HER2)-enriched, 64.9% versus 45.5%. p = 0.001; triple-negative, 73.6% versus 43.8%, p < 0.001). Low KIBRA expression was also associated with high nuclear grade (60.4% versus 37.8%, p < 0.001), high histologic grade (58.7% versus 37.0%, p < 0.001), and estrogen receptor (ER) negativity (54.2% versus 23.6%, p < 0.001). Low KIBRA expression was significantly associated with poor EFS (p = 0.041; hazard ratio (HR) 1.658; 95% confidence interval (CI), 1.015–2.709). Low KIBRA expression was an independent indicator of poor prognosis (p = 0.001; HR = 3.952; 95% CI = 1.542–10.133) in triple-negative breast cancer (TNBC). Conclusion: Low KIBRA expression was associated with higher histological grade, ER negativity and poor EFS of breast cancer. In particular, our data highlight KIBRA expression status as a potential prognostic marker for TNBC.

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Analysis of prolactin receptor expression in breast cancer subtypes

Biomeditsinskaya Khimiya ◽

10.18097/pbmc20206601089 ◽

2020 ◽

Vol 66 (1) ◽

pp. 89-94

Author(s):

T.S. Kalinina ◽

V.V. Kononchuk ◽

S.V. Sidorov ◽

L.F. Gulyaeva

Keyword(s):

Breast Cancer ◽

Triple Negative ◽

Prolactin Receptor ◽

Mrna Level ◽

Receptor Expression ◽

Mrna Levels ◽

Luminal A ◽

Her2 Positive ◽

Tissue Samples ◽

Luminal B

Breast cancer (BC) is the most common cancer among women. It is known that the prolactin receptor (PRLR) may play a role in breast carcinogenesis, but the available data are often contradictory. To get a more complete picture of the relationship between the receptor and mammary gland carcinogenesis, we examined the association between changes in PRLR expression level and tumor subtype (and its main characteristics). To do this, using real-time PCR, we evaluated the level of PRLR mRNA in BC tissue samples and untransformed adjoining tissue samples (89 pairs). Since the androgen receptor (AR) has begun to be seen as a prognostic marker in breast cancer, we also evaluated the association between mRNA levels of AR and PRLR. We found a significant increase in PRLR expression in luminal subtypes; the highest level of PRLR mRNA was detected in luminal A subtype. In HER2-positive ER-, PR-negative BC, the PRLR mRNA level decreases in tumor tissues compared with untransformed tissues. High PRLR expression is also associated with smaller tumor size in luminal B HER2-negative subtype. In ER-, PR-negative tumors, PRLR expression is associated with AR expression: PRLR mRNA level is increased when AR mRNA level is reduced by more than 8 times in triple-negative tumors; in contrast, in HER2-positive subtype it decreases more significantly when AR expression is reduced by more than 3 times. A tendency towards an increase in PRLR expression with an increase in the AR mRNA level was also discovered in luminal subtypes. The level of PRLR expression depends on the age of patients. In luminal A, PRLR expression is higher in patients under 65 years. In contrast, in luminal B HER2-negative and triple-negative BC, reduced PRLR expression was observed in patients under the age of 40 years and under the age of 50 years, respectively. In this group of patients under the age of 40 years with luminal B HER2-negative BC, ER expression was also reduced (0-4 score according to the IHC assay). Thus, PRLR probably plays a different role in the development and progression of BC: in luminal A and luminal B HER2-positive subtypes PRLR may act as an oncogen, and in luminal B HER2-negative and ER-, PR-negative subtypes can play a tumor suppressor role.

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Basal-like Breast Cancer—Characteristics, Risks, and Associations

Oncology & Hematology Review (US) ◽

10.17925/ohr.2012.08.1.26 ◽

2012 ◽

Vol 08 (01) ◽

pp. 26

Author(s):

Andrew Y Shuen ◽

William D Foulkes ◽

◽

Keyword(s):

Breast Cancer ◽

Massively Parallel Sequencing ◽

Target Identification ◽

Response To Therapy ◽

Breast Cancers ◽

Luminal A ◽

Luminal B ◽

Predictors Of Response ◽

Epidemiological Risk ◽

Basal Like Breast Cancer

Breast cancer is a heterogeneous disease. Gene expression profiling has demonstrated the existence of at least five ‘intrinsic’ subtypes: luminal A, luminal B, human epidermal growth factor-2 receptor (HER2), normal-like, and basal-like. While the estrogen receptor (ER), progesterone receptor (PR), and HER2 remain the most important prognostic markers and predictors of response to therapy, interrogating thousands of genetic transcripts more accurately captures the biological complexity and clinical heterogeneity of this disease. Target identification through massively parallel sequencing is likely to bear fruit in the coming years. Attention to basal-like breast cancers has grown substantially due to their generally poor prognosis, lack of targeted therapies, and connection withBRCA1-related cancers. In this article, we discuss the basal-like subgroup with respect to its cellular origins, relationship toBRCA1, and associated epidemiological risk factors.

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Identification of a Low-Risk Luminal A Breast Cancer Cohort That May Not Benefit From Breast Radiotherapy

Journal of Clinical Oncology ◽

10.1200/jco.2014.57.7999 ◽

2015 ◽

Vol 33 (18) ◽

pp. 2035-2040 ◽

Cited By ~ 73

Author(s):

Fei-Fei Liu ◽

Wei Shi ◽

Susan J. Done ◽

Naomi Miller ◽

Melania Pintilie ◽

...

Keyword(s):

Breast Cancer ◽

Epidermal Growth Factor Receptor ◽

Growth Factor ◽

High Risk ◽

Growth Factor Receptor ◽

Low Risk ◽

Luminal A ◽

Breast Radiotherapy ◽

Luminal B ◽

Epidermal Growth

Purpose To determine the prognostic and predictive value of intrinsic subtyping by using immunohistochemical (IHC) biomarkers for ipsilateral breast relapse (IBR) in participants in an early breast cancer randomized trial of tamoxifen with or without breast radiotherapy (RT). Patients and Methods IHC analysis of estrogen receptor, progesterone receptor, human epidermal growth factor receptor 2 (HER2), cytokeratin 5/6, epidermal growth factor receptor, and Ki-67 was conducted on 501 of 769 available blocks. Patients were classified as luminal A (n = 265), luminal B (n = 165), or high-risk subtype (luminal HER2, n = 22; HER2 enriched, n = 13; basal like, n = 30; or triple-negative nonbasal, n = 6). Median follow-up was 10 years. Results Classification by subtype was prognostic for IBR (10-year estimates: luminal A, 5.2%; luminal B, 10.5%; high-risk subtypes, 21.3%; P < .001). Luminal subtypes seemed to derive less benefit from RT (luminal A hazard ratio [HR], 0.40; luminal B HR, 0.51) than high-risk subtypes (HR, 0.13); however, the overall subtype-treatment interaction term was not significant (P = .26). In an exploratory analysis of women with clinical low-risk (age older than 60 years, T1, grade 1 or 2) luminal A tumors (n = 151), 10-year IBR was 3.1% versus 11.8% for the high-risk cohort (n = 341; P = .0063). Clinical low-risk luminal A patients had a 10-year IBR of 1.3% with tamoxifen versus 5.0% with tamoxifen plus RT (P = .42). Multivariable analysis showed that RT (HR, 0.31; P < .001), clinical risk group (HR, 2.2; P = .025), and luminal A subtype (HR, 0.25; P < .001) were significantly associated with IBR. Conclusion IHC subtyping was prognostic for IBR but was not predictive of benefit from RT. Further studies may validate the exploratory finding of a low-risk luminal A group who may be spared breast RT.

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