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Purpose: Estrogen receptor positive (ER+) breast cancer constitutes almost 85% of all breast cancer patients and are a genetically highly heterogenic group. Data on the association of somatic alterations to outcome and prognosis are however sparse. In this neoadjuvant endocrine phase II trial including postmenopausal breast cancer patients with ER+, HER2 normal breast cancer, we investigated the rate of pathogenic mutations before and after treatment as well as the association with treatment response and survival., Methods: Pretreatment and posttreatment tumour samples from 109 patients treated with neoadjuvant letrozole were collected and analysed with Next Generation Sequencing utilizing a panel of 12 genes (ALK, BRAF, EGFR, ERBB2, ERBB3, ESR1, KIT, KRAS, NRAS, PDGFRA, PIK3CA, and RAF1). Residual disease was assessed by a modified Miller Payne scale and the Residual Cancer Burden index. Survival data were collected prospectively., Results: Among the 109 patients, 52 had at least one pathogenic mutation in the pretreatment sample and 60 in the posttreatment sample. The most frequently mutated gene was PIK3CA, followed by EGFR and KRAS. Twelve different pathogenic PIK3CA mutations were identified, primarily in exon 20 and exon 9. An altered PIK3CA mutation profile from the pre- to the posttreatment specimen was significantly associated to improved pathological outcome. Overall and Disease-Free Survival benefits in PIK3CA mutated patients was observed., Conclusion: Considerable heterogeneity was identified both among patients and between pre- and posttreatment samples. PIK3CA has the potential to be a predictive biomarker. To further assess the implications of a treatment related altered PIK3CA mutation profile, more data are needed.

Purpose: Breast-contour preservation (BCP) is possible for most women treated for early-stage breast cancer. BCP can be defined as primary breast-conserving treatment (BCT), neoadjuvant chemotherapy (NAC) followed by BCT and immediate postmastectomy breast reconstruction (IBR). This study provides insight in current BCP strategies in Denmark and the Netherlands and aims to identify opportunities for improvement within both countries., Methods: A total of 92,881 patients with early-stage breast cancer who were operated in Denmark and the Netherlands between 2012 and 2017 were selected from the Danish Breast Cancer Group and the Dutch National Breast Cancer Audit databases. BCP procedures and predictive factors were analyzed within and between both countries., Results: BCP was achieved in 76.7% (n = 16,355) of the Danish and in 74.5% (n = 53,328) of the Dutch patients. While BCP rate did not change significantly over time in Denmark (p = 0.250), a significant increase in BCP rate from 69.5% in 2012 to 78.5% in 2017 (p < 0.001) was observed in the Netherlands. In both countries, variation in BCP rates between hospitals decreased over time. NAC followed by BCT and postmastectomy IBR was substantially more often used in the Netherlands compared to Denmark, specifically in patients younger than 50 years., Conclusions: In more than 75% of all Danish and Dutch patients, surgically treated for early-stage breast cancer, the breast-contour was preserved. The different use of BCP strategies within Denmark and the Netherlands and the differences observed between hospitals in both countries emphasize the need for more (inter)national consensus on treatment modalities.

Purpose: To determine the incidence and risk factors of sentinel lymph node (SN) and non-SN metastases in patients with microinvasive breast cancer (MIBC, T1 mic ). This to identify MIBC patients in whom axillary staging can be safely omitted., Methods: The Danish Breast Cancer Group database was used to identify a total of 409 women with breast cancer ≤ 1 mm who underwent sentinel lymph node biopsy (SLNB) between 2002 and 2015. After validation, 233 patients were eligible for the analysis. The incidence rates of SN and non-SN metastases were determined. The associations between clinicopathological variables and a positive SN [pN1, pN1mi, or pN0(i+)] were analyzed using univariate and multivariate designs., Results: Of 233 patients with MIBC, only 9 (3.9%) had SN macrometastases. An additional 18 (7.7%) and 23 (9.9%) had SN micrometastases and isolated tumor cells (ITCs), respectively. Of patients with SN macrometastases, two (22.2%) had non-SN macrometastases. In the adjusted analysis, a positive SN was associated with younger age (P = 0.0001) and a positive human epidermal growth factor 2 receptor (HER2) status (P = 0.03)., Conclusions: The low incidence of SN macrometastases < 4% suggests omission of axillary staging in MIBC patients without staging at primary surgery, especially in older (≥ 50 years) HER2 - patients. Still, the relatively high proportion of patients with non-SN macrometastases indicates that axillary treatment might be considered in SN positive patients, especially in younger HER2 + MIBC patients.

Purpose: How a second breast cancer diagnosis affects survival in comparison with unilateral breast cancer (UBC) is unclear. Prognostic factors for contralateral breast cancer (CBC) are also not well established. We aimed to investigate the survival pattern after CBC with particular focus on time between first and second breast cancer diagnosis and age at CBC diagnosis., Methods: Within the nationwide Danish Breast Cancer Cooperative Group database, we identified 68,466 breast cancer patients diagnosed during 1978-2012. Patients who subsequently developed CBC were identified in a previously established database (N = 3004). Patients were followed for breast cancer-specific death in the Danish Register of Causes of Death until 2015. Hazard ratios (HRs) and 95% confidence intervals (CIs) were calculated using Cox proportional hazard regression models. Cumulative breast cancer mortality from date of CBC was estimated using the Aalen-Johansen method., Results: Compared with UBC patients, the rate of dying from breast cancer was more than twofold higher following a CBC diagnosis, after adjustment for age, period, tumor characteristics, and treatment of the first breast cancer (HR 2.48; 95% CI 2.31-2.66). Short time interval (< 5 years) was associated with higher breast cancer-specific mortality after CBC among patients < 70 years at CBC diagnosis compared with longer time intervals, but not among patients ≥ 70 years at CBC diagnosis., Conclusion: Breast cancer-specific mortality rates were markedly higher after compared with before a CBC diagnosis. We found higher breast cancer-specific mortality after CBC associated with a short interval between diagnoses among patients diagnosed with CBC before age 70 years.

Purpose: To evaluate the estrogen receptor coactivator amplified in breast cancer 1 (AIB1) as a prognostic marker, as well as a predictive marker for response to adjuvant tamoxifen and/or aromatase inhibitors, in early estrogen receptor-positive breast cancer., Method: AIB1 was analyzed with immunohistochemistry in tissue microarrays of the Danish subcohort (N = 1396) of the International Breast Cancer Study Group's trial BIG 1-98 (randomization between adjuvant tamoxifen versus letrozole versus the sequence of the two drugs)., Results: Forty-six percent of the tumors had a high AIB1 expression. In line with previous studies, AIB1 correlated to a more aggressive tumor-phenotype (HER2 amplification and a high malignancy grade). High AIB1 also correlated to higher estrogen receptor expression (80-100 vs. 1-79%), and ductal histological type. High AIB1 expression was associated with a poor disease-free survival (univariable: hazard ratio 1.35, 95% confidence interval 1.12-1.63. Multivariable: hazard ratio 1.29, 95% confidence interval 1.06-1.58) and overall survival (univariable: hazard ratio 1.34, 95% confidence interval 1.07-1.68. Multivariable: hazard ratio 1.25, 95% confidence interval 0.99-1.60). HER2 did not seem to modify the prognostic effect of AIB1. No difference in treatment effect between tamoxifen and letrozole in relation to AIB1 was found., Conclusions: In a subset of the large international randomized trial BIG 1-98, we confirm AIB1 to be a strong prognostic factor in early breast cancer. Hence, although tumor AIB1 expression does not seem to be useful for the choice of tamoxifen versus an aromatase inhibitor in postmenopausal endocrine-responsive breast cancer, AIB1 is an interesting target for new anti-cancer therapies and further investigations of this biomarker is warranted.

We estimated the impact of axillary lymph node dissection (ALND) on the risk of axillary recurrence (AR) and overall survival (OS) in breast cancer patients with micrometastases or isolated tumor cells (ITC) in sentinel nodes. We used the Danish Breast Cancer Cooperative Group (DBCG) database to identify patients with micrometastases or ITC in sentinel nodes following surgery for primary breast cancer between 2002 and 2008. A Cox proportional hazard regression model was developed to assess the hazard ratios (HR) for AR and OS between patients with and without ALND. We identified 2074 patients, of which 240 did not undergo further axillary surgery. The 5-year cumulated incidence for AR was 1.58 %. No significant difference in AR was seen between patients with and without ALND. The age adjusted HR for AR if ALND was omitted was 1.79 (95 % CI 0.41-7.80, P = 0.44) in patients with micrometastases and 2.21 (95 % CI 0.54-8.95, P = 0.27), in patients with ITC after a median follow-up of 6 years and 3 months. There was no significant difference in overall survival between patients with and without ALND, when adjusting for age, co-morbidity, tumor size, histology type, malignancy grade, lymphovascular invasion, hormone receptor status, adjuvant systemic treatment and radiotherapy, with a HR for death if ALND was omitted of 1.21 (95 % CI 0.86-1.69, P = 0.27) in patients with micrometastases and 0.96 (95 % CI 0.57-1.62, P = 0.89) in patients with ITC after a medium follow-up on 8 and 5 years. In this nationwide study, we found a low risk of AR on 1.58 % and we did not find a significantly increased risk of AR if ALND was omitted in patients with micrometastases or ITC in sentinel nodes. Furthermore, no significant difference in overall survival was seen between patients with and without ALND when adjusting for adjuvant treatment.

We examined the association between the hormone receptor (HR) and human epidermal growth factor receptor 2 (HER2) status of women with primary breast cancer and the risk of axillary lymph node (ALN) involvement at the time of diagnosis. Information on 20,009 women diagnosed with primary breast cancer between 2008 and 2012 was retrieved from the Danish Breast Cancer Cooperative Group database. The associations between clinical and pathological variables and ALN involvement at the time of diagnosis were evaluated in univariate and multivariate regression analyses, as well as the significance of tumor subtypes in ALN involvement. The risk of ALN metastases at the time of diagnosis was significantly reduced in HR-negative patients compared to HR-positive patients [adjusted odds ratio (OR) 0.69; 95 % CI 0.63-0.76; P = 0.0009]. A HER2-positive status was associated with an increased risk of ALN involvement at diagnosis compared to a HER2-negative status (OR 1.37; 95 % CI 1.24-1.50; P < 0.0001). An interaction between HER2 and HR was observed, with a HER2-positive status significantly associated with ALN involvement at the time of diagnosis only in HR-negative patients (P < 0.0001). The triple-negative breast cancer (TNBC) patients showed a significantly reduced risk of ALN involvement at the time of diagnosis compared to patients with HR-positive/HER2-negative tumors (OR 0.55; 95 % CI 0.49-0.62; P < 0.0001). The HR and HER2 statuses are significantly associated with ALN involvement at the time of diagnosis. Despite the poor prognosis, TNBC patients have a reduced risk of ALN involvement at the time of diagnosis compared to patients with other subtypes, when adjusting for other risk factors. This may indicate that TNBC tends to spread hematogenously rather than lymphogenously.

Docetaxel-induced peripheral neuropathy (PN) can lead to sub-optimal treatment in women with early breast cancer. Here, we compare the frequency of dose reduction as a result of PN in two different adjuvant regimens. From the Danish Breast Cancer Cooperative Group READ trial we included 1,725 patients with early stage breast cancer who randomly were assigned to three cycles of epirubicin and cyclophosphamide followed by three cycles docetaxel (D100) or six cycles of cyclophosphamide and docetaxel (D75). Eligible patients completed chemotherapy, received docetaxel, and provided information on patient-reported outcome (secondary outcome of trial) including PN. Associations between PN and risk factors were analyzed by multivariate logistic regression. Overall 597 patients (34 %) reported PN, grades 2-4, during treatment, 194 (11 %) after the first cycle [early onset peripheral neuropathy (EPN)] and 403 (23 %) after subsequent cycles [later-onset peripheral neuropathy (LPN)]. The odds ratio (OR) of EPN was significantly increased for the D100 regimen (OR 3.10; 95 % CI 2.18-4.42) while this regimen was associated with reduced OR of LPN (OR 0.69; 95 % CI 0.54-0.88). Patients with PN received significantly lower cumulative doses of docetaxel than patients with no PN. Explorative analysis showed that OR of PN was significantly reduced if patients wore frozen gloves and socks during treatment (OR 0.56; 95 % CI 0.38-0.81) in the EPN group. Patients developing PN after the first cycle are less likely to receive docetaxel at the planned dose intensity and usage of frozen gloves and socks may modify the risk.

Recently, many centers have omitted routine axillary lymph node dissection (ALND) after metastatic sentinel node biopsy in breast cancer due to a growing body of literature. However, existing guidelines of adjuvant treatment planning are strongly based on axillary nodal stage. In this study, we aim to develop a novel international multicenter predictive tool to estimate a patient-specific risk of having four or more tumor-positive axillary lymph nodes (ALN) in patients with macrometastatic sentinel node(s) (SN). A series of 675 patients with macrometastatic SN and completion ALND from five European centers were analyzed by logistic regression analysis. A multivariate predictive model was created and validated internally by 367 additional patients and then externally by 760 additional patients from eight different centers. All statistical tests were two-sided. Prevalence of four or more tumor-positive ALN in each center's series (P = 0.010), number of metastatic SNs (P < 0.0001), number of negative SNs (P = 0.003), histological size of the primary tumor (P = 0.020), and extra-capsular extension of SN metastasis (P < 0.0001) were included in the predictive model. The model's area under the receiver operating characteristics curve was 0.766 in the internal validation and 0.774 in external validation. Our novel international multicenter-based predictive tool reliably estimates the risk of four or more axillary metastases after identifying macrometastatic SN(s) in breast cancer. Our tool performs well in internal and external validation, but needs to be further validated in each center before application to clinical use.

During the past 50 years, breast cancer incidence has increased by 2-3 % annually. Despite many years of testing for estrogen receptors (ER), evidence is scarce on breast cancer incidence by ER status. The aim of this paper was to investigate the increase in breast cancer incidence by ER status. Data were obtained from the clinical database of the Danish Breast Cancer Cooperative Group which holds nationwide data on diagnosis, including pathology, treatment, and follow-up on primary breast cancers since 1977. All Danish women <80 years diagnosed with primary breast cancer 1996-2007 were identified in this prospective register based study. ER status was evaluated using immunohistochemical staining by standardized laboratory methods in the Danish Pathology Departments and reported to the database. From 1996 to 2007, breast cancer incidence increased overall with a tendency to level off after 2002. In all women a significant decrease was found in ER unknown tumors. However, in both pre- and postmenopausal women, significant increases were seen in incidence of ER+ tumors; though the increase levelled off for premenopausal women after 2002. In postmenopausal women, the incidence of ER- breast cancer decreased significantly throughout the period. In women <35 years, we found a minor non-significant increase in both ER+ and ER- tumors. ER unknown decreased in all women and was the most distinct in premenopausal women aged 35+. We found a significant increase in ER+ breast cancer incidence in postmenopausal women whereas the incidence in premenopausal women (aged 35+) levelled off after 2002.

The incidence of breast cancer, as well as other chronic disease, increases with age, older breast cancer patients being more likely than younger to suffer from other diseases at time of diagnosis. Our objective was to assess the effect of comorbidity on mortality after early breast cancer. 62,591 women diagnosed with early breast cancer 1990-2008 were identified using the Danish Breast Cancer Cooperative Group Registry. Data were linked to the Danish National Patient Register and the Danish Register of Causes of Death. Main outcome measures were mortality from all causes, breast cancer, and non-breast cancer causes in relation to Charlson comorbidity index (CCI). Compared with patients without comorbidity (CCI 0), the presence of comorbidity increased the risk of dying from breast cancer as well as other causes with adjusted hazard ratios (HRs) for all-cause mortality of 1.45 (CI 95% 1.40-1.51) for CCI 1, 1.52 (95% CI 1.45-1.60) for CCI 2, and 2.21 (95% CI 2.08-2.35) for CCI 3+. Equivalent HRs for breast cancer-specific mortality were 1.30 (95% CI, 1.24-1.36) for CCI 1, 1.31 (95% CI 1.23-1.39) for CCI 2, and 1.79 (95% CI, 1.66-1.93) for CCI 3+ (all P values < 0.0001). For patients with CCI 0, 5-year overall survival increased over time from 72.5% (95% CI, 71.7-73.3%) in 1990-1994 to 81.6% (95% CI, 80.9-82.2) in 2000-2004, whereas the 5-year overall survival remained stable around 43% among the patients with CCI 3+. This population-based cohort study shows that compared with patients without comorbidity, the risk of dying from breast cancer as well as other causes increased significantly with increasing CCI score. While survival improved over time for patients without comorbidity, no improvement was seen among patients with severe comorbidity (CCI 3+).

HER2 amplification, TOP2A aberrations, and absence of tissue inhibitor of metalloproteinase (TIMP-1) expression in breast carcinomas have been shown to be associated with incremental benefit from anthracycline-containing adjuvant chemotherapy, and this study was undertaken to validate these findings in a similar, but independent, randomized clinical trial. TIMP-1 was examined by immunohistochemistry in archival tumor tissue from 403 of 716 premenopausal high-risk patients with known HER2 and TOP2A status who were randomized to cyclophosphamide, epirubicin, and fluorouracil (CEF) or cyclophosphamide, methotrexate, and fluorouracil (CMF) in the MA.5 trial. Ninety-eight (24%) patients had no TIMP-1 staining of tumor cells, 27% were HER2 amplified, and 18% were TOP2A aberrant. Forty-four percentage was classified as HT responsive (HER2 amplified and/or TIMP-1 negative) and 37% as 2T responsive (TOP2A aberrant and/or TIMP-1 negative). There was no heterogeneity in treatment effect of CEF versus CMF according to TIMP-1. In HT-responsive patients, CEF was superior to CMF with an improved RFS (adjusted HR, 0.64; 95% CI, 0.42-0.97), but this was not significant for OS (adjusted HR, 0.66; 95% CI, 0.42-1.04). A significant HT profile versus treatment interaction was detected for OS (P = 0.03). In 2T-responsive patients, CEF seemed to improve RFS compared to CMF (adjusted HR, 0.67; 95% CI, 0.43-1.03) and improved OS (adjusted HR, 0.58; 95% CI, 0.36-0.93). A significant 2T profile versus treatment interaction was detected for OS (P = 0.01). With this study, we validate a more substantial reduction in mortality by CEF compared to CMF in patients with an HT- or 2T-responsive profile; however, we could not show a similarly significant reduction in RFS events, where a benefit of CEF over CMF was found irrespective of TIMP-1 status. Further studies are necessary before the HT and 2T profiles may be used to direct the use of anthracyclines.

Isolated tumor cells (ITC) are more common in the sentinel node (SN) after needle biopsy of a breast cancer, indicating iatrogenic displacement of tumor cells. We here investigate whether similar iatrogenic displacement occurs after surgical excision of a breast tumor. We compared the incidence of ITC in the SN of 414 breast cancer patients with recent surgical excision to a group of 16,960 patients without recent surgical procedure in a multivariate analysis by linking data from the Danish Breast Cancer Cooperative Group database and the Danish National Health Register. Moreover, the incidence of spread to non-SNs in patients with ITC in the SN after recent surgical excision was analyzed. We found an adjusted odds ratio on 3.73 (95% CI 2.57-5.43; P < 0.0001) for having ITC in the SN after surgical excision. The increase in ITC after surgical excision was especially seen in patients with ductal carcinomas (OR 4.66; 95% CI 3.03-7.19). None of the patients with ITC in SN after surgical excision had further spread to non-SNs compared to 12% in the group without recent surgical excision (P = 0.09). The nearly fourfold increase in ITC in the SN after surgical excision indicates that this procedure induces iatrogenic displacement of tumor cells. This displacement was more common in ductal carcinomas. We found no further dissemination to non-SNs in patients with ITC in the SN after recent surgical excision, and it is questioned whether these patients benefit from an axillary lymph node dissection.

The aim of this study was to examine TOP2A gene copy number changes as a means to identify groups of breast cancer patients with superior benefit from treatment with anthracyclines. Tumour tissue was retrospectively collected and successfully analysed for TOP2A in 773 of 980 Danish patients randomly assigned to receive intravenous CMF (cyclophosphamide, methotrexate and fluorouracil) or CEF (cyclophosphamide, epirubicin and fluorouracil) in DBCG trial 89D. Subgroup analyses on this material published by Knoop et al. (J Clin Oncol 23:7483-7490, 2005) and updated by Nielsen et al. (Acta Oncol 47:725-734, 2008) demonstrated that superiority of CEF over CMF is limited to patients with TOP2A aberrations, defined as patients whose tumours have TOP2A ratio below 0.8 or above 2.0. The Subpopulation Treatment Effect Pattern Plot (STEPP) technique was applied to these data to explore the pattern of treatment effect relative to TOP2A and to compare that pattern to the ranges previously used to define 'aberrations'. The pattern of treatment effect illustrated by the STEPP analysis confirmed that the superiority of CEF over CMF is indeed limited to patients whose tumours have high or low TOP2A ratios. The hypothesis of no treatment effect-covariate interaction was rejected (P = 0.02). Furthermore, results indicated that the interval of TOP2A ratios hitherto denoted as 'normal' could be narrower than previously assumed. A more optimal separation of TOP2A subgroups could be obtained by altering cut-points currently used to define TOP2A amplified and TOP2A deleted tumours by narrowing the TOP2A normal interval, and consequently enlarging the population with TOP2A aberrated tumours.

YKL-40 is a new biomarker in serum with a prognostic value in several localized and metastatic malignancies. The current knowledge regarding the biological functions of YKL-40 in cancer links YKL-40 to increased aggressiveness of the tumor. Utilizing tissue microarrays, YKL-40 protein expression in tumor tissue was assessed by immunohistochemistry in a cohort of 630 high-risk breast cancer patients with a median estimated potential follow-up time of 10 and 13 years for disease-free (DFS) and overall survival (OS), respectively. YKL-40 protein expression was found in malignant tumor cells and in inflammatory cells. High expression was associated with positive estrogen and progesterone receptor status and high tumor differentiation. Contrary to studies on serum YKL-40 as a prognostic biomarker, a high YKL-40 expression in tumor cells was not significantly associated with DSF and OS in univariate and multivariate analyses.