Serial single-cell RNA sequencing unveils drug resistance and metastatic traits in stage IV breast cancer.

Metastasis is a complex process that remains poorly understood at the molecular levels. We profiled single-cell transcriptomic, genomic, and epigenomic changes associated with cancer cell progression, chemotherapy resistance, and metastasis from a Stage IV breast cancer patient. Pretreatment- and posttreatment-specimens from the primary tumor and distant metastases were collected for single-cell RNA sequencing and subsequent cell clustering, copy number variation (CNV) estimation, transcriptomic factor estimation, and pseudotime analyses. CNV analysis revealed that a small population of pretreatment cancer cells resisted chemotherapy and expanded. New clones including Metastatic Precursor Cells (MPCs), emerged in the posttreatment primary tumors in CNV similar to metastatic cells. MPCs exhibited expression profiles indicative of epithelial-mesenchymal transition. Comparison of MPCs with metastatic cancer cells also revealed dynamic changes in transcription factors and calcitonin pathway gene expression. These findings demonstrate the utility of single-patient clinical sample analysis for understanding tumor drug resistance, regrowth, and metastasis.

Chromatin conformational changes at human satellite II contribute to the senescence phenotype in the tumor microenvironment.

Cellular senescence and senescence-associated secretory phenotype (SASP) in stromal cells within the tumor microenvironment promote cancer progression. Although cellular senescence has been shown to induce changes in the higher-order chromatin structure and abnormal transcription of repetitive elements in the genome, the functional significance of these changes is unclear. In this study, we examined the human satellite II (hSATII) loci in the pericentromere to understand these changes and their functional significance. Our results indicated that the hSATII loci decompact during senescence induction, resulting in new DNA-DNA interactions in distinct genomic regions, which we refer to as DRISR (Distinctive Regions Interacted with Satellite II in Replicative senescent Fibroblasts). Interestingly, decompaction occurs before the expression of hSATII RNA. The DRISR with altered chromatin accessibility was enriched for motifs associated with cellular senescence and inflammatory SASP genes. Moreover, DNA-fluorescence in situ hybridization analysis of the breast cancer tissues revealed hSATII decompaction in cancer and stromal cells. Furthermore, we reanalyzed the single-cell assay for transposase-accessible chromatin with sequencing data and found increased SASP-related gene expression in fibroblasts exhibiting hSATII decompaction in breast cancer tissues. These findings suggest that changes in the higher-order chromatin structure of the pericentromeric repetitive sequences during cellular senescence might directly contribute to the cellular senescence phenotype and cancer progression via inflammatory gene expression.

Validation of the prognosis of patients with ER­positive, HER2­negative and node­negative invasive breast cancer classified as low risk by Curebest™ 95GC Breast in a multi­institutional registry study.

Curebest™ 95GC breast (95GC) is a multigene classifier we developed for the prognostic prediction of patients with estrogen receptor (ER)-positive, human epidermal growth factor receptor 2 (HER2)-negative and node-negative (ER+/HER2-/n0) invasive breast cancer treated with adjuvant endocrine therapy alone. The aim of the preset study was to evaluate the clinical utility of 95GC in a multiinstitutional registry study. Patients (n=215) with ER+/HER2-/n0 invasive breast cancer who had undergone the 95GC assay in seven hospitals were consecutively recruited in the registry study at various postoperative times. At recruitment, no patients had disease recurrences and were prospectively followed up for a median of 62 (range, 6-91) postoperative months. Of the 124 patients classified as 95GC low risk, 118 received adjuvant endocrine therapy alone and six received adjuvant chemo-endocrine therapy. Only two patients developed distant recurrences, and the 5-year distant recurrence-free survival (DRFS) was as high as 98.0%. Of the 91 patients classified as 95GC high risk, 81 received adjuvant chemo-endocrine therapy and 10 received adjuvant endocrine therapy alone. A total of four of these patients developed distant recurrences (5-year DRFS=95.5%). Among the 95GC high-risk patients, prognosis was significantly improved for the 81 treated with adjuvant chemo-endocrine therapy compared with for the 77 (historical controls) treated with adjuvant endocrine therapy alone (P=0.0002; hazard ratio, 0.24). Compared with the St. Gallen 2013 guideline, a significant de-escalation from 73.1% (155/212) to 40.6% (86/212) in adjuvant chemotherapy was achieved. The excellent prognosis of patients with ER+/HER2-/n0 invasive breast cancer classified as 95GC low risk could be validated in the present registry study, indicating that 95GC is useful for safe de-escalation of adjuvant chemotherapy in patients with ER+/HER2-/n0 invasive breast cancer.

Effectiveness and tasks of breast MRI surveillance for high-risk women with cancer susceptibility genes other than BRCA1/2: a single institution study.

BACKGROUND: In Japan, with the introduction of multigene panel testing, there is an urgent need to build a new medical system for hereditary breast cancer patients that covers pathogenic variants other than BRCA1/2. The aim of this study was to reveal the current status of breast MRI surveillance for high-risk breast cancer susceptibility genes other than BRCA1/2 and the characteristics of detected breast cancer. METHODS: We retrospectively examined 42 breast MRI surveillance with contrast performed on patients with hereditary tumors other than BRCA1/2 pathogenic variants at our hospital from 2017 to 2021. MRI exams were evaluated independently by two radiologists. Final histopathological diagnosis for malignant lesions were obtained from surgical specimen. RESULTS: A total of 16 patients included TP53, CDH1, PALB2, ATM pathogenic variants and 3 variant of unknown significance. 2 patients with TP53 pathogenic variants were detected breast cancer by annual MRI surveillance. The rate of cancer detection was 12.5% (2/16). One patient was detected synchronous bilateral breast cancer and unilateral multiple breast cancers (3 lesions in 1 patient), so there were 4 malignant lesions in total. Surgical pathology of 4 lesions were 2 ductal carcinoma in situ, 1 invasive lobular carcinoma, and 1 invasive ductal carcinoma. MRI findings of 4 malignant lesions were detected as 2 non mass enhancement, 1 focus and 1 small mass. All of 2 patients with PALB2 pathogenic variants had previously developed breast cancer. CONCLUSIONS: Germline TP53 and PALB2 were strongly associated with breast cancer, suggesting that MRI surveillance is essential for breast cancer-related hereditary predisposition.

Chromatin profile-based identification of a novel ER-positive breast cancer subgroup with reduced ER-responsive element accessibility.

BACKGROUND: Oestrogen receptor (ER) signalling-dependent cancer cell growth is one of the major features of ER-positive breast cancer (BC). Inhibition of ER function is a standard and effective treatment for ER-positive tumours; however, ~20% of patients with ER-positive BC experience early or late recurrence. In this study, we examined intertumour heterogeneity from an epigenetic perspective based on the hypothesis that the intrinsic difference in epigenetic states around ER signalling pathway underlies endocrine therapy resistance. METHODS: We performed transposase-accessible chromatin sequencing (ATAC-seq) analysis of 42 BC samples, including 35 ER-positive(+) human epidermal growth factor receptor 2 (HER2)-negative(-) and 7 triple-negative tumours. We also reanalysed ATAC-seq data of 45 ER + /HER2 - tumours in the Cancer Genome Atlas (TCGA) BC cohort to validate our observations. RESULTS: We conducted a comprehensive analysis of cis-regulatory elements (CREs) using ATAC-seq, identifying three subgroups based on chromatin accessibility profiles. We identified a subgroup of ER-positive BCs with a distinctive chromatin accessibility pattern including reduced accessibility to ER-responsive elements (EREs). The same subgroup was also observed in TCGA BC cohort. Despite the reduced accessibility to EREs, the expression of ER and potential ER target genes were not decreased in these tumours. CONCLUSION: Our findings highlight the existence of a subset of ER-positive BCs with unchanged ER expression but reduced EREs accessibility that cannot be distinguished by conventional immunostaining for ER. Future studies should determine whether these tumours are associated with resistance to endocrine therapy.

Transcriptomic intratumor heterogeneity of breast cancer patient-derived organoids may reflect the unique biological features of the tumor of origin.

BACKGROUND: The intratumor heterogeneity (ITH) of cancer cells plays an important role in breast cancer resistance and recurrence. To develop better therapeutic strategies, it is necessary to understand the molecular mechanisms underlying ITH and their functional significance. Patient-derived organoids (PDOs) have recently been utilized in cancer research. They can also be used to study ITH as cancer cell diversity is thought to be maintained within the organoid line. However, no reports investigated intratumor transcriptomic heterogeneity in organoids derived from patients with breast cancer. This study aimed to investigate transcriptomic ITH in breast cancer PDOs. METHODS: We established PDO lines from ten patients with breast cancer and performed single-cell transcriptomic analysis. First, we clustered cancer cells for each PDO using the Seurat package. Then, we defined and compared the cluster-specific gene signature (ClustGS) corresponding to each cell cluster in each PDO. RESULTS: Cancer cells were clustered into 3-6 cell populations with distinct cellular states in each PDO line. We identified 38 clusters with ClustGS in 10 PDO lines and used Jaccard similarity index to compare the similarity of these signatures. We found that 29 signatures could be categorized into 7 shared meta-ClustGSs, such as those related to the cell cycle or epithelial-mesenchymal transition, and 9 signatures were unique to single PDO lines. These unique cell populations appeared to represent the characteristics of the original tumors derived from patients. CONCLUSIONS: We confirmed the existence of transcriptomic ITH in breast cancer PDOs. Some cellular states were commonly observed in multiple PDOs, whereas others were specific to single PDO lines. The combination of these shared and unique cellular states formed the ITH of each PDO.

Clinical significance of the neutrophil-to-lymphocyte ratio in oligometastatic breast cancer.

PURPOSE: This study investigated the clinical impact of pretreatment neutrophil-to-lymphocyte ratio (NLR) on survival in patients with oligometastatic breast cancer. PATIENTS AND METHODS: We collected data from 397 patients who underwent primary breast surgery from 2004 to 2015 and developed recurrence during the follow-up. We reviewed the images and clinical information and defined OMD according to the European Society for Medical Oncology advanced breast cancer guidelines. The NLR was calculated using pretreatment data of primary breast cancer. The cutoff value of the NLR was determined by receiver operating characteristic curve with Youden Index. RESULTS: Among 397 patients, 131 had OMD at recurrence. The low-NLR group included patients of significantly older age at primary cancer than those in the high-NLR group. A low NLR indicated a better overall survival (p = 0.023) after adjusting for relevant factors, including estrogen receptor status, surgical resection of metastatic disease, metastatic organ number, disease-free interval, and liver metastasis than did the high-NLR group. We developed prognostic models for OMD using six independent prognostic factors, including the NLR. The number of factors was associated with overall survival; patients with all six favorable factors showed a good overall survival of 90.9% at 8 years and those with four or more factors showed 70.4%. CONCLUSIONS: The NLR was an independent prognostic factor for overall survival in OMD. The number of favorable prognostic factors was associated with overall survival. A prognostic model, including the NLR, will help identify patients with a favorable prognosis.

GRHL2 motif is associated with intratumor heterogeneity of cis-regulatory elements in luminal breast cancer.

In breast cancer patients, tumor heterogeneity is associated with prognosis and therapeutic response; however, the epigenetic diversity that exists in primary tumors remains unknown. Using a single-cell sequencing assay for transposase-accessible chromatin (scATAC-seq), we obtained the chromatin accessibility profiles of 12,452 cells from 16 breast cancer patients including 11 luminal, 1 luminal-HER2, 1 HER2+, and 3 triple-negative subtypes. Via this profiling process, tumors were classified into cancer cells and the tumor microenvironment, highlighting the heterogeneity of disease-related pathways including estrogen receptor (ER) signaling. Furthermore, the coexistence of cancer cell clusters with different ER binding motif enrichments was identified in a single ER+ tumor. In a cluster with reduced ER motif enrichment, we identified GRHL2, a transcription factor, as the most enriched motif, and it cooperated with FOXA1 to initiate endocrine resistance. Coaccessibility analysis revealed that GRHL2 binding elements potentially regulate genes associated with endocrine resistance, metastasis, and poor prognosis in patients that received hormonal therapy. Overall, our study suggests that epigenetic heterogeneity could lead to endocrine resistance and poor prognosis in breast cancer patients and it offers a large-scale resource for further cancer research.

The ELEANOR noncoding RNA expression contributes to cancer dormancy and predicts late recurrence of estrogen receptor-positive breast cancer.

The recurrence risk of estrogen receptor (ER)-positive breast cancer remains high for a long period of time, unlike other types of cancer. Late recurrence reflects the ability of cancer cells to remain dormant through various events, including cancer stemness acquisition, but the detailed mechanism is unknown. ESR1 locus enhancing and activating noncoding RNAs (ELEANORS) are a cluster of nuclear noncoding RNAs originally identified in a recurrent breast cancer cell model. Although their functions as chromatin regulators in vitro are well characterized, their roles in vivo remain elusive. In this study, we evaluated the clinicopathologic features of ELEANORS, using primary and corresponding metastatic breast cancer tissues. The ELEANOR expression was restricted to ER-positive cases and well-correlated with the ER and progesterone receptor expression levels, especially at the metastatic sites. ELEANORS were detected in both primary and metastatic tumors (32% and 29%, respectively), and frequently in postmenopausal cases. Interestingly, after surgery, patients with ELEANOR-positive primary tumors showed increased relapse rates after, but not within, 5 years. Multivariate analysis showed that ELEANORS are an independent recurrence risk factor. Consistently, analyses with cell lines, mouse xenografts, and patient tissues revealed that ELEANORS upregulate a breast cancer stemness gene, CD44, and maintain the cancer stem cell population, which could facilitate tumor dormancy. Our findings highlight a new role of nuclear long noncoding RNAs and their clinical potential as predictive biomarkers and therapeutic targets for late recurrence of ER-positive breast cancer.

Assessment of a cancer genomic profile test for patients with metastatic breast cancer.

Comprehensive cancer genomic profile (CGP) tests are being implemented under Japanese universal health insurance system. However, the clinical usefulness of CGP test for breast cancer patients has not been evaluated. Of the 310 patients who underwent CGP testing at our institution between November 2019 and April 2021, 35 patients with metastatic breast cancer whose treatment strategy was discussed by our molecular tumor board within the study period were investigated after exclusion of 2 cases that could not be analyzed. The turn-around time, drug accessibility, and germline identification detection were evaluated. The subtype was luminal in 20 patients (57.1%), triple-negative in 12 patients (34.3%), and luminal-HER2 in 3 patients (8.6%). Actionable gene mutations were detected in 30 patients (85.7%), and 7 patients (20.0%) were recommended for clinical trial participation, with the drug administered to 2 patients (5.7%). Three patients (8.6%) died due to disease progression before the test results were disclosed. We report the results of an initial assessment of the utility of CGP testing for patients with metastatic breast cancer under Japanese universal health insurance system. Conducting CGP tests at a more appropriate time could provide patients with greater benefit from treatments based on their specific gene mutations.

A prediction model for early systemic recurrence in breast cancer using a molecular diagnostic analysis of sentinel lymph nodes: A large-scale, multicenter cohort study.

BACKGROUND: The one-step nucleic acid amplification (OSNA) assay can quantify the cytokeratin 19 messenger RNA copy number as a proxy for sentinel lymph node (SN) metastasis in breast cancer. A large-scale, multicenter cohort study was performed to determine the prognostic value of the SN tumor burden based on a molecular readout and to establish a model for the prediction of early systemic recurrence in patients using the OSNA assay. METHODS: SN biopsies from 4757 patients with breast cancer were analyzed with the OSNA assay. The patients were randomly assigned to the training or validation cohort at a ratio of 2:1. On the basis of the training cohort, the threshold SN tumor burden value for stratifying distant recurrence was determined with Youden's index; predictors of distant recurrence were investigated via multivariable analyses. Based on the selected predictors, a model for estimating 5-year distant recurrence-free survival was constructed, and predictive performance was measured with the validation cohort. RESULTS: The prognostic cutoff value for the SN tumor burden was 1100 copies/µL. The following variables were significantly associated with distant recurrence and were used to construct the prediction model: SN tumor burden, age, pT classification, grade, progesterone receptor, adjuvant cytotoxic chemotherapy, and adjuvant anti-human epidermal growth factor receptor 2 therapy. The values for the area under the curve, sensitivity, specificity, and accuracy of the prediction model were 0.83, 63.4%, 81.7%, and 81.1%, respectively. CONCLUSIONS: Using the OSNA assay, the molecular readout-based SN tumor burden is an independent prognostic factor for early breast cancer. This model accurately predicts early systemic recurrence and may facilitate decision-making related to treatment.

Distinct Clinicopathologic Features and Possible Pathogenesis of Localized ALK-positive Histiocytosis of the Breast.

Anaplastic lymphoma kinase (ALK)-positive histiocytosis is a rare emerging entity characterized by systemic or localized proliferation of histiocytes harboring ALK rearrangements. Breasts are reportedly affected by ALK-positive histiocytosis. Here, we evaluated 2 localized cases of breast ALK-positive histiocytosis through a comprehensive clinicopathologic, molecular, and genomic analysis to further delineate this entity and better understand its pathogenesis. The cases involved 2 undiagnosed ALK-positive spindle-cell breast lesions. Both cases were Asian women aged 30s to 40s who underwent excisions for asymptomatic breast masses. Macroscopically, both lesions were well-circumscribed, solid masses. Microscopically, both lesions were predominantly composed of fascicles with uniform, bland spindle cells, admixed with epithelioid histiocyte-like cells and lymphoid aggregates. Immunohistochemically, the spindle and epithelioid cells coexpressed ALK and histiocytic markers (eg, CD68, CD163). Genetically, both lesions harbored KIF5B-ALK, confirmed by fluorescence in situ hybridization and polymerase chain reaction-direct sequencing analyses. Combining these results, both cases were successfully diagnosed as ALK-positive histiocytosis. Furthermore, no common or previously annotated somatic alterations were identified by whole-exome sequencing. One case harbored clonal immunoglobulin gene rearrangements according to the polymerase chain reaction-based BIOMED-2 protocol. Therefore, ALK-positive histiocytosis can be accurately diagnosed through a combination of morphologic, immunohistochemical, and molecular analyses. In this entity, breast cases may have distinct clinicopathologic features: Asian women aged 30s to 40s, asymptomatic masses, and predominant spindled morphology. For pathogenesis, ALK rearrangements could be the driver alteration, and a subset of ALK-positive histiocytosis may harbor a lymphoid lineage. These findings can be utilized to improve the diagnosis of ALK-positive histiocytosis and better understand its pathogenesis.

Assessment of axillary node status by ultrasound after neoadjuvant chemotherapy in patients with clinically node-positive breast cancer according to breast cancer subtype.

The use of sentinel node biopsy (SNB) following neoadjuvant chemotherapy (NAC) for patients with cN1 breast cancer is controversial. Improvements of negative predictive value (NPV) by axillary ultrasound (AUS), which corresponds to the accurate prediction rate of node-negative status after NAC, would lead to decreased FNR of SNB following NAC. In this study, we retrospectively investigated the accurate prediction rate of NPV by AUS after NAC in patients with cytologically node-positive breast cancer treated between January 2012 and December 2016. Of 279 eligible patients, the NPV was 49.2% in all patients, but varied significantly by tumor subtype (p < 0.001) and tumor response determined by magnetic resonance imaging (MRI) (p = 0.0003). Of the 23 patients with clinically node negative (ycN0) by AUS and clinical complete response in primary lesion by MRI, the NPV was 100% in patients with HR±/HER2+ or HR-/HER2- breast cancer. In conclusion, regarding FNR reduction post-NAC, it will be of clinical value to take tumor subtype and primary tumor response using MRI into account to identify patients for SNB after NAC.

Myofibroblastoma of the breast showing rare palisaded morphology and uncommon desmin- and CD34-negative immunophenotype: A case report.

Myofibroblastoma is a rare benign mesenchymal tumor typically arising in the breast. We report a diagnostically challenging case of myofibroblastoma of the breast showing a rare palisaded morphology and an uncommon desmin- and CD34-negative immunophenotype. A 73-year-old man underwent an excision for an 8 mm-sized breast mass. Histology revealed that the tumor was composed of fascicles of bland spindle cells showing prominent nuclear palisading and Verocay-like bodies. First, schwannoma, malignant peripheral nerve sheath tumor, and synovial sarcoma were suspected given the palisaded morphology. However, none of them was confirmed by immunohistochemical or molecular analyses. Next, a palisaded variant of myofibroblastoma was suspected by the morphology and coexpression of estrogen, progesterone and androgen receptors, BCL2 and CD10 in immunohistochemistry. However, the key diagnostic markers, desmin and CD34, were both negative. Finally, the diagnosis of myofibroblastoma was confirmed by detecting RB1 loss in immunohistochemistry and monoallelic 13q14 deletion (RB1 and FOXO1 loss) by fluorescence in situ hybridization assay. For the correct diagnosis of myofibroblastoma, it is important for pathologists to recognize the wide morphological spectrum, including a palisaded morphology, and the immunophenotypical variations, including desmin- and CD34-negative immunophenotypes, and to employ a comprehensive diagnostic analysis through combined histological, immunohistochemical and molecular evaluations.

Metastatic ovarian cancer spreading into mammary ducts mimicking an in situ component of primary breast cancer: a case report.

BACKGROUND: Accurate diagnosis of metastatic tumors in the breast is crucial because the therapeutic approach is essentially different from primary tumors. A key morphological feature of metastatic tumors is their lack of an in situ carcinoma component. Here, we present a unique case of metastatic ovarian carcinoma spreading into mammary ducts and mimicked an in situ component of primary carcinoma. To our knowledge, this is the second case (and the first adult case) confirming the in situ-mimicking growth pattern of a metastatic tumor using immunohistochemistry. CASE PRESENTATION: A 69-year-old Japanese woman was found to have a breast mass with microcalcifications. She had a known history of ovarian mixed serous and endocervical-type mucinous (seromucinous) carcinoma. Needle biopsy specimen of the breast tumor revealed adenocarcinoma displaying an in situ-looking tubular architecture in addition to invasive micropapillary and papillary architectures with psammoma bodies. From these morphological features, metastatic serous carcinoma and invasive micropapillary carcinoma of breast origin were both suspected. In immunohistochemistry, the cancer cells were immunoreactive for WT1, PAX8, and CA125, and negative for GATA3, mammaglobin, and gross cystic disease fluid protein-15. Therefore, the breast tumor was diagnosed to be metastatic ovarian serous carcinoma. The in situ-looking architecture showed the same immunophenotype, but was surrounded by myoepithelium confirmed by immunohistochemistry (e.g. p63, cytokeratin 14, CD10). Thus, the histogenesis of the in situ-like tubular foci was could be explained by the spread of metastatic ovarian cancer cells into existing mammary ducts. CONCLUSION: Metastatic tumors may spread into mammary duct units and mimic an in situ carcinoma component of primary breast cancer. This in situ-mimicking growth pattern can be a potential pitfall in establishing a correct diagnosis of metastasis to the breast. A panel of breast-related and extramammary organ/tumor-specific immunohistochemical markers may be helpful in distinguishing metastatic tumors from primary tumors.

Pathogenicity assessment of variants for breast cancer susceptibility genes based on BRCAness of tumor sample.

Genes involved in the homologous recombination repair pathway-as exemplified by BRCA1, BRCA2, PALB2, ATM, and CHEK2-are frequently associated with hereditary breast and ovarian cancer syndrome. Germline mutations in the loci of these genes with loss of heterozygosity or additional somatic truncation at the WT allele lead to the development of breast cancers with characteristic clinicopathological features and prominent genomic features of homologous recombination deficiency, otherwise referred to as "BRCAness." Although clinical genetic testing for these and other genes has increased the chances of identifying pathogenic variants, there has also been an increase in the prevalence of variants of uncertain significance, which poses a challenge to patient care because of the difficulties associated with making further clinical decisions. To overcome this challenge, we sought to develop a methodology to reclassify the pathogenicity of these unknown variants using statistical modeling of BRCAness. The model was developed with Lasso logistic regression by comparing 116 genomic attributes derived from 37 BRCA1/2 biallelic mutant and 32 homologous recombination-quiescent breast cancer exomes. The model showed 95.8% and 86.7% accuracies in the training cohort and The Cancer Genome Atlas validation cohort, respectively. Through application of the model for variant reclassification of homologous recombination-associated hereditary breast and ovarian cancer causal genes and further assessment with clinicopathological features, we finally identified one likely pathogenic and five likely benign variants. As such, the BRCAness model developed from the tumor exome was robust and provided a reasonable basis for variant reclassification.

Efficacy of radiation boost after breast-conserving surgery for breast cancer with focally positive, tumor-exposed margins.

Many patients with positive margins following breast-conserving surgery (BCS) undergo re-excisions that aim to remove residual disease from the breast, which brings a tremendous emotional burden in addition to financial consequences. We sought to determine whether re-excisions could be safely avoided without compromising local control and survival by using whole-breast radiation therapy (WBRT) with a tumor bed boost in patients with early-stage breast cancer with focally positive, tumor-exposed margins after BCS. All patients with ductal carcinoma in situ (DCIS) and/or invasive breast cancer (IBC) who had pathologically tumor-exposed margins following BCS, without re-excision and treated with WBRT with tumor bed boost between March 2005 and December 2011, were included. The radiotherapy consisted of WBRT at a dose of 50 Gy in 25 fractions, followed by a tumor bed boost with an additional dose of 16 Gy in eight fractions. A total of 125 patients fulfilled the eligibility criteria; of the 125 patients, 1 had bilateral breast cancer, resulting in 126 cases. Invasive disease was found in 102 (81%) cases and purely ductal carcinoma in situ (DCIS) disease in 24 (19%) cases. The 10-year ipsilateral breast tumor recurrence (IBTR) -free survival, progression-free survival (PFS), and 10-year overall survival (OS) rates were 95%, 92.5% and 96%, respectively. Patients with early-stage breast cancer who receive BCS and have focally positive, tumor-exposed margins can avoid re-excision by undergoing WBRT followed by a sufficient dose of tumor bed boost, without negatively impacting local control and survival.