High levels of serum CA15-3 and residual invasive tumor size are associated with poor prognosis for breast cancer patients with non-pathological complete response after neoadjuvant chemotherapy.

BACKGROUND AND OBJECTIVES: To identify surrogate markers for prognosis of breast cancer patients with non-pathological complete response (non-pCR) to neoadjuvant chemotherapy (NAC), our investigation focused on the serum levels of carcinoembryonic antigen (CEA) and carbohydrate antigen (CA15-3) as well as clinicopathological factors both before and after NAC. METHODS: A total of 185 breast cancer patients treated with NAC were recruited. Serum carcinoembryonic antigen and CA15-3 were measured at baseline and at completion of NAC. RESULTS: Among the non-pCR cancers (n = 142), the disease-free survival (DFS) of patients with CA15-3-low at baseline (3-year DFS: 0.908, n = 73) was significantly better than of those with CA15-3-high (3-year DFS: 0.681, n = 69, P = .0134). Multivariable analysis demonstrated that baseline CA15-3 levels (hazard ratio: 3.31, 95% confidence interval: 1.28-10.23; P = .0122) and residual invasive size (hazard ratio: 4.47, 1.26-28.39; P = .0171) were significant independent factors for DFS. The combination of these factors proved to be an accurate predictor for DFS regardless of breast cancer subtypes. CONCLUSIONS: The combination of residual invasive size and serum CA15-3 levels at baseline seems to be a significant and independent surrogate marker of poor outcome for patients with non-pCR. These findings suggest that these markers may be useful for identifying patients with inferior prognosis and candidates for additional adjuvant treatments.

Independent prognostic impact of preoperative serum carcinoembryonic antigen and cancer antigen 15-3 levels for early breast cancer subtypes.

BACKGROUND: Although the prognosis for operable breast cancers is reportedly worse if serum carcinoembryonic antigen (CEA) and cancer antigen 15-3 (CA15-3) levels are above normal, the usefulness of this prognosis is limited due to the low sensitivity and specificity; in addition, the optimal cutoff levels remain unknown. METHODS: A total of 1076 patients who were operated for breast cancers (test set = 608, validation set = 468) without evidence of metastasis were recruited, and their baseline and postoperative serum CEA and CA15-3 levels were analyzed. The optimal cutoff values of CEA and CA15-3 for disease-free survival (DFS) were 3.2 ng/mL and 13.3 U/mL, respectively, based on receiver operating characteristic curve and area under the curve analyses. RESULTS: The DFS of patients with high CEA levels (CEA-high: n = 191, 5-year DFS 70.6%) was significantly worse (p < 0.0001) than that of CEA-low patients (n = 885, 5-year DFS 87.2%). There was a significant difference in DFS (p < 0.0001) between CA15-3-high and CA15-3-low patients (n = 314 and n = 762, respectively; 5-year DFS 71.8 vs. 89.3%). Significant associations between DFS and CA15-3 levels were observed irrespective of the subtypes. Multivariable analysis indicated that tumor size, lymph node metastasis, tumor grade, and CEA (p = 0.0474) and CA15-3 (p < 0.0001) levels were independent prognostic factors (hazard ratio [HR] 1.520, 95% confidence interval [CI] 1.005-2.245 for CEA; HR 2.088, 95% CI 1.457-2.901 for CA15-3). CONCLUSIONS: These findings suggest that CEA and CA15-3 levels might be useful for predicting the prognosis of patients with operable early breast cancer irrespective of the subtype. Serum levels at baseline may reflect tumor characteristics for metastatic potential even when these levels are within the normal ranges.

Impact of biomarker changes during neoadjuvant chemotherapy for clinical response in patients with residual breast cancers.

BACKGROUND: Residual cancer burden or Ki67 expression levels in residual tumors reportedly provided significant prognostic information for a non-pathological complete response subset after neoadjuvant chemotherapy (NAC). However, the significance of Ki67 reduction for clinical response during chemotherapy in each subtype or menopausal status is yet to be determined. METHODS: A total of 183 breast cancers surgically removed after chemotherapy were recruited for this study. Expression levels of estrogen receptor (ER), progesterone receptor (PgR), and Ki67 were determined immunohistochemically for semiquantitative measurement and these biomarkers were compared in pre- and post-NAC samples from pathological non-responders (n = 125). Responses to chemotherapy were evaluated both clinically and pathologically. RESULTS: Ki67 expression levels after NAC (median 5 %, range 0-70 %) were significantly reduced compared with before NAC (25, 1-80 %, P < 0.0001), but only in patients who attained clinical response. This significant suppression of Ki67 in clinical responders was consistently observed in breast cancers from the ER-positive subset, but not the ER-negative subset in the total test set (n = 120). These observations were also made in the validation set (n = 63). Among premenopausal, but not postmenopausal patients, a significant decrease in PgR expression levels was detected in breast cancers of patients who attained clinical response (pre-NAC 50, 0-100 %, post-NAC 5, 0-20 %; P = 0.0003). CONCLUSION: The impact of Ki67 suppression on clinical response seems to be restricted to ER-positive breast cancers. Since PgR expression levels of premenopausal ER-positive cancers were significantly reduced in clinical responders, inhibition of estrogen signaling due to chemotherapy-induced amenorrhea may be involved in this association.

High levels at baseline of serum pyridinoline crosslinked carboxyterminal telopeptide of type I collagen are associated with worse prognosis for breast cancer patients.

It is speculated that adjuvant use of bisphosphonate reduces recurrence in breast cancer patients through suppression of bone resorption. To determine the prognostic impact of bone resorption markers, we investigated serum levels of the pyridinoline crosslinked carboxyterminal telopeptide of type I collagen (1CTP) and N-terminal crosslinking telopeptides of type I collagen (NTX). 1CTP and NTX were measured at baseline (before operation or neoadjuvant therapies) and afterward in 469 patients operated on breast cancer. The optimal cutoff value of 1CTP for relapse-free survival (RFS) was set at 3.6 ng/ml with an area under the receiver operating characteristics curve of 0.641 [95% confidence interval (CI) = 0.560-0.721; p = 0.0011]. However, we were unable to determine a significant cutoff value for NTX. RFS was significantly worse for 1CTP-high patients with than for those with low levels of 1CTP (p = 0.0002). Multivariate analysis with tumor size, lymph node metastasis, and nuclear grade showed that 1CTP was a significant independent prognostic factor (hazard ratio = 2.04, 95% CI = 1.13-3.68; p = 0.018). Worse prognosis for the subset with high 1CTP levels applied only to postmenopausal patients (p = 0.0002). RFS of 130 patients whose 1CTP changed from low at baseline to high at 6 months postoperatively showed RFS almost as poor as that for patients with high 1CTP throughout. These findings suggest that 1CTP may be useful not only for identifying patients with unfavorable prognosis, but also for selecting patients who may benefit from administration of bone-modifying agents in an adjuvant setting.

Association between ¹8F-FDG uptake and molecular subtype of breast cancer.

PURPOSE: To determine whether (18)F-FDG uptake in breast cancer correlates with immunohistochemically defined subtype and is able to predict molecular subtypes. METHODS: This retrospective study involved 306 patients with 308 mass-type invasive breast cancers (mean size 2.65 cm, range 1.0-15.0 cm) who underwent (18)F-FDG PET/CT before therapy. The correlations between primary tumour (18)F-FDG uptake on PET/CT, expressed as SUVmax, and clinicopathological findings and molecular subtype, i.e. luminal A, luminal B (HER2-negative), luminal B (HER2-positive), HER2-positive and triple-negative, were analysed. The predictors of these subtypes were investigated. RESULTS: The mean SUVmax of the 308 tumours was 5.33 ± 3.63 (range 1.15-19.01). Among the subtypes of the 308 tumours, 87 (28.2 %) were luminal A, 111 (36.0 %) were luminal B (HER2-negative), 31 (10.1 %) were luminal B (HER2-positive), 26 (8.4 %) were HER2-positive and 53 (17.2 %) were triple-negative, and the corresponding mean SUVmax were 3.41 ± 2.07 (range 1.18-14.30), 5.17 ± 3.52 (range 1.35-19.01), 6.57 ± 3.84 (range 1.42-15.58), 7.55 ± 3.63 (range 2.30-13.60) and 6.97 ± 4.17 (range 1.15-16.06), respectively. A cut-off value of 3.60 yielded 70.1 % sensitivity and 66.1 % specificity with an area under the receiver operating characteristics curve (AUC) of 0.734 for predicting that a tumour was of the luminal A subtype. A cut-off value of 6.75 yielded 65.4 % sensitivity and 75.2 % specificity with an AUC of 0.704 for predicting a HER2-positive subtype. CONCLUSION: SUVmax, a metabolic semiquantitative parameter, shows a significant correlation with the molecular subtype of breast cancer, and is useful for predicting the luminal A or HER2-positive subtype.

Baseline neutrophil-to-lymphocyte ratio and c-reactive protein predict efficacy of treatment with bevacizumab plus paclitaxel for locally advanced or metastatic breast cancer.

The effect of bevacizumab plus paclitaxel therapy on progression-free survival (PFS) is prominent; however, no overall survival (OS) benefit has been demonstrated. Our aim was to study the predictive efficacy of peripheral immune-related parameters, neutrophil-to-lymphocyte ratio (NLR), absolute lymphocyte count (ALC), and c-reactive protein (CRP) in locally advanced and metastatic breast cancers. A total of 179 patients treated with bevacizumab plus paclitaxel were recruited from three institutes in the test cohort. The cut-off values of NLR, ALC, and CRP were set at 3, 1500/µL, and 1.0 mg/dL, respectively, and baseline values of these factors were measured. The PFS of patients with NLR-low was significantly longer than that of patients with -high (median, 12.6 vs. 7.2 months; hazard ratio (HR), 0.48, 95% confidence interval (95% CI), 0.31-0.73; p = 0.0004). OS of patients with NLR-low was significantly better than those with-high (22.2 vs. 13.5 months; HR, 0.57, 95% CI, 0.39-0.83; p = 0.0032). Similarly, improved PFS and OS were recognized in patients with CRP-low as compared with patients with -high (HR, 0.44, 95% CI, 0.28-0.68; p = 0.0001 and HR, 0.39, 95% CI, 0.26-0.61, p < 0.0001, respectively). In the validation cohort from two institutes (n = 57), similar significant improvements in PFS and OS were confirmed for patients with NLR-low (p = 0.0344 and p = 0.0233, respectively) and CRP-low groups (p < 0.0001 and p = 0.0001, respectively). Low levels of NLR and CRP at baseline were significantly associated with improved prognosis in patients treated with bevacizumab plus paclitaxel.

Significant Association Between Low Baseline Neutrophil-to-Lymphocyte Ratio and Improved Progression-free Survival of Patients With Locally Advanced or Metastatic Breast Cancer Treated With Eribulin But Not With Nab-Paclitaxel.

INTRODUCTION: Although eribulin and nab-paclitaxel are chemotherapy agents widely used for locally advanced or metastatic breast cancer (MBC), their predictive factors remain unknown. Because the absolute neutrophil-to-lymphocyte ratio (NLR) is a significant prognostic factor for early-stage breast cancer, we investigated its usefulness in terms of the eribulin or nab-paclitaxel treatment efficacy for MBC. PATIENTS AND METHODS: A total of 85 patients with MBC treated with eribulin (n = 59) or nab-paclitaxel (n = 26) were recruited. NLR values were collected at baseline, after 1 cycle, after 2 cycles, and at the end of treatment. The NLR cutoff value was set at 3. RESULTS: The progression-free survival (PFS) of patients with an NLR < 3 at baseline (median, 242 days; n = 24) was significantly better than that of patients with an NLR of ≥ 3 (median, 98 days; n = 35; hazard ratio, 0.37, 95% confidence interval, 0.18-0.71; P = .0032). Similarly, the overall survival was marginally significantly better in patients with an NLR < 3 who were treated with eribulin (P = .058). However, the NLR was not significantly associated with PFS or overall survival for patients treated with nab-paclitaxel. No significant association was found between the NLR during treatment and PFS in the eribulin group. The significance of the NLR for the efficacy of eribulin was consistent, irrespective of estrogen receptor status, previous anthracycline or endocrine use, and the number of previous chemotherapy regimens. CONCLUSION: A low NLR at baseline was significantly associated with improved PFS in patients treated with eribulin but not in those treated with nab-paclitaxel. Therefore, the baseline NLR might be clinically useful for selecting patients who would benefit from eribulin.

Two giant renal aneurysms and renal arteriovenous fistula associated with cardiac insufficiency and a sustained elevation of atrial natriuretic peptide and brain natriuretic peptide.

A 64-year-old man presented with chief complaints of exertional dyspnea and palpitation. He had previously undergone left nephrolithotomies twice. A chest roentgenogram showed pleural effusion on both sides with cardiac dilation, and electrocardiography showed a frequent occurrence of ventricular premature contractions. An echocardiogram showed diffuse hypokinesis of the left ventricular wall motion (ejection fraction, 45%) and dilation of the left ventricle (left ventricular end-diastolic dimension, 61 mm). We administered diuretics, ACE inhibitors and a beta-adrenergic blocking agent after making a diagnosis of cardiac insufficiency. Because coronary angiography showed 90% stenosis of the left anterior descending coronary artery (No. 7), we performed coronary angioplasty in this locus. Though both the left ventricular wall motion and ejection fraction improved, and the clinical symptoms disappeared, the left ventricular end-diastolic dimension, and arrhythmia did not improve. Furthermore, the brain natriuretic peptide increased despite these treatments. Thereafter, a left renal artery aneurysm (extrarenal aneurysm measuring 5 cm in diameter and an intrarenal aneurysm measuring 3 cm in diameter) and a left renal arteriovenous fistula were discovered when abdominal echography was performed because of epigastric discomfort. As a result, a left total nephrectomy was performed. Subsequently, the left ventricular end-diastolic dimension and arrhythmia improved, and the brain natriuretic peptide returned to a normal value. We herein report a case that developed cardiac insufficiency due to a renal aneurysm and renal arteriovenous fistula after undergoing left nephrolithotomies twice.

Different patterns of change in bone turnover markers during treatment with bone-modifying agents for breast cancer patients with bone metastases.

BACKGROUND: Bone-modifying agents are effective for treatment of breast cancer patients with bone metastases. Since their action is mediated through suppression of the osteoclast function, their efficacy can be determined by monitoring bone turnover markers. However, the clinical significance of these markers is yet to be compared. METHODS: For this study, 52 breast cancer patients with bone metastases treated with zoledronic acid (n = 36) or denosumab (n = 22) were enrolled (6 patients were treated sequentially with both agents). Serum tartrate-resistant acid phosphatase-5b (TRACP-5b), pyridinoline cross-linked carboxyterminal telopeptide of type I collagen (1CTP), N-terminal cross-linking telopeptides of type I collagen (NTX) and bone-specific alkaline phosphatase (BAP) were measured at pretreatment and 1, 3 and 6 months after treatment. RESULTS: Serum TRACP-5b (p < 0.0001), NTX (p = 0.0007) and BAP (p = 0.0032) decreased significantly after treatment. The baseline median value of TRACP-5b (457.5 mU/dL, range 173-1630 mU/dL) decreased to 137 mU/dL (91-795 mU/dL) 1 month after treatment. Reduction in serum NTX and BAP was greatest after 3 and 6 months, respectively. TRACP-5b, NTX and BAP were above normal levels at baseline in 62.5, 25 and 35.3 % of patients, respectively, and nearly 80 % of these patients attained normal levels during the treatment. CONCLUSIONS: Although bone-modifying agents reduced the baseline levels of TRACP-5b, NTX and BAP significantly, the reduction patterns differed. TRACP-5b appears to affect levels most quickly and sensitively, possibly due to its direct link to the number and activity of osteoclasts. These findings suggest that the efficacy of TRACP-5b is clinically significant when considering which bone-modifying agents to use for breast cancer patients with bone metastases.

Tumor size and proliferative marker geminin rather than Ki67 expression levels significantly associated with maximum uptake of 18F-deoxyglucose levels on positron emission tomography for breast cancers.

It has been well established that maximum standardized uptake value (SUVmax) for 18F-fluorodeoxyglucose positron-emission tomography/computed tomography (FDG PET/CT) is clinically useful for evaluating treatment efficacy as well as predicting prognosis of breast cancer patients. Although SUVmax reflects increased glucose uptake and metabolism possibly induced by activation of growth factor signaling or TP53 dysfunction, tumor characteristics of SUVmax-high breast cancers remain to be elucidated. For the present study, we used immunohistochemical staining to investigate expressions of phospho-ribosomal protein S6 (pS6, downstream molecule of phosphatidyl inositol 3-kinase/Akt/mammalian target of the rapamycin/S6K pathway) and phosphor-p44/42 mitogen-activated protein kinase (pMAPK). Expression levels of TP53 and proliferative marker geminin as well as Ki67 were also examined by means of immunostaining in 163 invasive breast cancers. Cutoff values were set at 10% for pS6, 20% for pMAPK and TP53, and 4% for geminin. The SUVmax levels were significantly higher in the pS6-positive (p = 0.0173), TP53-positive (p = 0.0207) and geminin-high cancers (p<0.0001), but there was no significant association between pMAPK expression levels and SUVmax levels. Multivariable analysis showed that a high geminin level (odds ratio: 6.497, 95% confidence interval: 2.427-19.202, p = 0.0001) and large tumor size (6.438, 2.224-20.946, p = 0.0005) were significantly and independently associated with SUVmax-high. Univariable but not multivariable analysis indicated that Ki67-high significantly correlated with SUVmax-high. Twenty of 23 (87.0%) breast cancers with tumor size >2cm and geminin-high showed SUVmax-high, while only 6 of 49 (12.2%) breast cancers ≤2cm in size and with low geminin levels were SUVmax-high. In conclusion, we could determine that breast cancers with a large tumor and a geminin-high rather than Ki67-high proliferative marker were significantly associated with high levels of SUVmax. These findings may signify that SUVmax reflects tumor characteristics with high proliferative activity but not activation of mTOR/S6K and MAPK pathways or increased glucose metabolism due to dysfunction of TP53.

Prognostic significance of geminin expression levels in Ki67-high subset of estrogen receptor-positive and HER2-negative breast cancers.

BACKGROUND: Indication for chemotherapy in estrogen receptor (ER)-positive and human epidermal growth factor receptor 2 (HER2)-negative breast cancers is determined on the basis of Ki67 expression level. However, since Ki67-high cancers are not necessarily sensitive to chemotherapy, identification of such patients who do not need chemotherapy is an important issue. PATIENTS AND METHODS: We used immunohistochemical staining to examine the expression levels of ER, progesterone receptor (PgR), Ki67, and geminin, a marker of S to G2/M phases, in 80 ER-positive/HER2-negative breast cancers. The labeling indices of Ki67 and geminin were determined and cutoff values were set at 15 and 6 %, respectively. RESULTS: Ki67 and geminin expression levels were significantly associated with nuclear grade. In the Ki67-low subset, 26 out of 28 (92.9 %) cancers were geminin low and in the Ki67-high subset, 31 out of 52 (59.6 %) were geminin high. Distant disease-free survival (DDFS) of the geminin-high subset was significantly poorer than that of the geminin-low subset (P = 0.009). In the Ki67-low subset, only one patient showed recurrence. Metastasis was detected in eight out of 31 (25.8 %) patients in the geminin-high group of the Ki67-high subset, but no recurrence was observed in the geminin-low group of the Ki67-high subset. CONCLUSION: Geminin-high breast cancers are significantly associated with worse prognosis. Since poorer prognosis was recognized only in the geminin-high group in Ki67-high cancers, we speculate that geminin may be useful for identifying patients in the Ki67-high subset who can avoid unnecessary chemotherapy.

Prognostic significance of preoperative 18F-FDG PET/CT for breast cancer subtypes.

Adjuvant treatments for operable breast cancers are determined according to subtypes defined based on estrogen receptor (ER) and human epidermal growth factor receptor 2 (HER2) status. The ER+/HER2- subtype can be divided into luminal A and luminal B usually by Ki67 expression levels. Although tumor size, lymph node metastasis and tumor grade have been widely accepted in daily clinical practice, the identification of further prognostic indicators especially in the ER+/HER2- subtype is warranted. A total of 387 operated breast cancers for which maximum standardized uptake value (SUVmax) on the 18F-fluorodeoxyglucose positron-emission tomography/computed tomography (FDG PET/CT) were available at baseline were retrospectively analyzed. The optimal cutoff value of SUVmax for relapse-free survival (RFS) was determined to be 3.585 by means of the receiver operating characteristics curve with an area under the curve of 0.6795 (95% CI: 0.5972 to 0.7618, p = 0.0006, sensitivity: 78.8%, specificity: 57.1%). The RFS of patients with SUVmax-high (n = 178) was significantly (p = 0.0003) worse compared with those with SUVmax-low (n = 209). This significant association was prominently recognized in the ER+/HER2- subtype. By multivariable analysis, SUVmax (hazard ratio: 3.83, 95% confidence interval: 1.28-11.51, p = 0.017), tumor size (4.22, 1.39-12.82, p = 0.011) and lymph node metastasis (4.44, 1.81-10.87, p = 0.0012) were significant and independent prognostic factors for RFS. The ER+/HER2- subtype demonstrated consistently worse RFS in the SUVmax-high patients both in the luminal A (p = 0.037) and luminal B (p = 0.047) subtypes. Combination of Ki67 and SUVmax appears to be useful for selecting patients who have inferior prognosis and need further adjuvant treatment of the ER+/HER2- subtype.

High Ki-67 Expression and Low Progesterone Receptor Expression Could Independently Lead to a Worse Prognosis for Postmenopausal Patients With Estrogen Receptor-Positive and HER2-Negative Breast Cancer.

UNLABELLED: We examined the prognostic significance of progesterone receptor (PgR) expression in immunohistochemical-based luminal subtypes defined by Ki-67 expression, taking menopausal status into consideration. The study included 327 surgically removed estrogen receptor-positive and human epidermal growth factor receptor 2-negative breast cancers. High Ki-67 expression (> 15%) and low PgR expression (£ 20%) were significant independent factors resulting in worse distant relapse-free survival. This association was observed in postmenopausalwomen but not in premenopausal women. BACKGROUND: Accurate classification of luminal A and luminal B characteristics of estrogen receptor (ER)-positive and human epidermal growth factor receptor 2 (HER2)-negative breast cancer is considered clinically important for determining effective adjuvant treatment. Although Ki-67 expression has been identified as an essential constituent for this classification, the role of progesterone receptor (PgR) expression has yet to be fully elucidated. Because PgR expression is influenced by the estrogen milieu, we examined the prognostic significance of PgR expression in immunohistochemical (IHC)-based luminal subtypes defined by Ki-67 expression, taking menopausal status into consideration. MATERIALS AND METHODS: We examined 327 surgically removed ER(+) and HER2(-) breast cancer specimens. ER, PgR, and Ki67 expression was determined IHC for semiquantitative measurement. We used 1%, 20%, and 15% as the cutoff value for ER, PgR, and Ki-67, respectively. RESULTS: Breast cancer with low PgR (≤ 20%) expression was significantly associated with postmenopausal status, a large tumor size, and low ER expression. The low PgR expression subset had significantly worse distant relapse-free survival (DRFS) than the high PgR expression subset (P = .0067). This association was observed consistently in postmenopausal women but not in the premenopausal women. Multivariate analysis demonstrated that high Ki-67 expression (hazard ratio [HR], 3.80; 95% confidence interval [CI], 1.57-10.58; P = .003) and low PgR expression (HR, 2.54; 95% CI, 1.08-6.40; P = .038) were significant independent factors affecting DRFS. CONCLUSION: Low PgR expression was independently associated with a poorer prognosis for ER(+) and HER2(-) breast cancer. Determination of PgR expression combined with that of Ki-67 could thus improve the accuracy of IHC-based classification of luminal A and luminal B breast cancer, especially for postmenopausal women.

Activation of mTOR/S6K But Not MAPK Pathways Might Be Associated With High Ki-67, ER(+), and HER2(-) Breast Cancer.

UNLABELLED: We determined the activation of the phosphoinositide 3-kinase (PI3K) and mitogen-activated protein kinase (MAPK) signaling pathways in 108 cases of estrogen receptor-positive and human epidermal growth factor receptor 2-negative breast cancer with high and low Ki-67 expression. The expression levels of Ki-67, p53, phosphorylated MAPK (pMAPK), and protein S6 (pS6; downstream molecule of PI3K/Akt/mammalian target of rapamycin/S6 kinase pathway) were determined immunohistochemically. pS6 positivity, but not pMAPK positivity, was significantly associated with the high Ki-67 expression subset. BACKGROUND: Evaluation of luminal A and luminal B characteristics of estrogen receptor (ER)-positive and human epidermal growth factor receptor 2 (HER2)-negative breast cancer is considered important. Although the phosphoinositide 3 kinase (PI3K) and mitogen-activated protein kinase (MAPK) signaling pathways are thought to be involved in the luminal B subtype, the details of their contribution to breast cancer remain unclear. MATERIALS AND METHODS: We determined the activation of these pathways (phosphorylated MAPK [pMAPK] and protein S6 [pS6; a downstream molecule of PI3K/Akt/mammalian target of rapamycin (mTOR)/S6 kinase (S6K)]) in 108 ER(+), HER2(-) breast cancer cases with high and low Ki-67 expression. The ER, progesterone receptor (PgR), Ki-67, p53 expression levels were also determined immunohistochemically. The cutoff value for Ki-67 was set at 15%. RESULTS: A significantly greater percentage of cancer cases with high Ki-67 expression showed pS6 positivity than did those with low Ki-67 expression (53.2% vs. 19.7%; P = .0003). No significant differences were found between the cases with high and low expression levels were detected for p53 (23.4% vs. 11.5%; P = .12) or pMAPK (36.2% vs. 34.4%; P = .85) positivity. Multivariate analysis showed that pS6 positivity (odds ratio 5.16, 95% confidence interval 1.95-13.63; P = .0009), nuclear grade 2 and 3, and low PgR expression (≤ 20%) were independently associated with the high Ki-67 subset. CONCLUSION: From our findings, we have concluded that the pS6 expression level is associated with the characteristics of breast cancer with high Ki-67 expression. Because these associations were observed, irrespective of menopausal status, the biologic difference seems to be less affected by estrogen signaling than by activation of S6 protein, especially in terms of proliferation. Our findings have also indicated that targeting the mTOR/S6K pathway might be a useful strategy for the treatment of ER(+)/HER2(-) breast cancer with high Ki-67 expression.