Nomogram for predicting preoperative lymph node involvement in patients with invasive micropapillary carcinoma of breast: a SEER population-based study.

BACKGROUND: Invasive micropapillary carcinoma (IMPC) is an unusual and distinct subtype of invasive breast tumor with high propensity for regional lymph node metastases. This study was to identify risk factors accounting for IMPC of the breast and to develop a nomogram to preoperatively predict the probability of lymph node involvement. METHODS: A retrospective review of the clinical and pathology records was performed in patients diagnosed with IMPC between 2003 and 2014 from Surveillance, Epidemiology, and End Results (SEER) database. The cohort was divided into training and validation sets. Training set comprised patients diagnosed between 2003 and 2009, while validation set included patients diagnosed thereafter. A logistic regression model was used to construct the nomogram in the training set and then varified in the validation set. Nomogram performance was quantified with respect to discrimination and calibration using R 3.4.1 software. RESULTS: Overall, 1407 patients diagnosed with IMPC were enrolled, of which 527 in training set and 880 in validation set. Logistic regression analysis indicated larger lesions, younger age at diagnosis, black ethnic and lack of hormone receptor expression were significantly related to regional nodes involvement. The AUC of the nomogram was 0.735 (95% confidential interval (CI) 0.692 to 0.777), demonstrating a good prediction performance. Calibration curve for the nomogram was plotted and the slope was close to 1, which demonstrated excellent calibration of the nomogram. The performance of the nomogram was further validated in the validation set, with AUC of 0.748 (95% CI 0.701 to 0.767). CONCLUSIONS: The striking difference between IMPC and IDC remains the increased lymph node involvement in IMPC and therefore merits aggressive treatment. The nomogram based on the clinicalpathologic parameters was established, which could accurately preoperatively predict regional lymph node status. This nomogram would facilitate evaluating lymph node state preoperatively and thus treatment decision-making of individual patients.

Erratum: KCNN4 induces multiple chemoresistance in breast cancer by regulating BCL2A1.

[This corrects the article on p. 3302 in vol. 10, PMID: 33163271.].

Clinicopathologic profiling and oncologic outcomes of secretory carcinoma of the breast.

Secretory carcinoma of the breast (SCB) is a rather rare entity of invasive breast cancer, the clinicopathologic characteristics and survival outcomes remain to be elaborated. A retrospective review was conducted in SEER database. A total of 190 SCB patients identified in SEER were eligible for inclusion in the analysis. Median age at diagnosis was 56 years (range 2-96 years). Both sexes and bilateral breast could be affected. Intriguingly, the incidence of SCB tended towards to decreasing in recent decades. Small tumor burden was observed with a mean tumor size of 2.13 cm. In a subgroup with sufficient details, positive staining of estrogen receptor (ER) and progesterone receptor (PR) was 58% and 40%, respectively. The vast majority of patients were of well to moderate differentiation (86.86%) and negative regional lymph nodes involvement (70.71%). Nearly half of the patients took radiotherapy and chemotherapy. Seniors were inclined to have an inferior breast cancer specific survival (BCSS) than their younger counterparts (P = 0.018). Patients underwent breast conserving surgery (BCS) and radiotherapy had much better BCSS than its mastectomy counterparts (P = 0.014). Collectively, SCB is a clinical indolent invasive breast cancer with excellent prognosis. BCS in conjunction with radiotherapy would be a rational alternative for this distinct entity.

Outcomes and risk of subsequent breast events in breast-conserving surgery patients with BRCA1 and BRCA2 mutation.

PURPOSE: Previous studies provide inconsistent interpretations of the effect of inherited genetic factors on the survival and prognosis of patients with breast cancer. The aim of this study was to examine the effect of germline BRCA1 and BRCA2 mutation on survival and subsequent breast events in Chinese women who underwent breast-conserving surgery. METHODS: A retrospective review of the clinical and pathological records was performed in patients diagnosed with primary invasive breast cancer between 2005 and 2018 in the cancer registry database. Clinicopathological data and data regarding treatment and outcomes, including date and site of disease progression, were collected. The survival outcomes and independent risk factors were conducted using SPSS. RESULTS: Overall, a total of 501 patients who underwent breast-conserving surgery were identified and subjected to analyses, of which 63 cases with BRCA1 or BRCA2 mutation. The median age at diagnosis was 41 (range, 24-74) for carriers and 37 (range, 17-84) for noncarriers. After a median follow-up time of 61 months (range, 8-161) and 70 months (range, 0-153), respectively, in carriers and noncarriers, the overall survival (P = .173) and disease-free survival (P = .424) were not significantly different. Analogously, there was no significant difference between the two groups about the outcomes of ipsilateral breast tumor recurrence (P = .348), yet the contralateral breast cancer (CBC) was overt worse than noncarriers (P < .001). When adjusted to confounding factors, BRCA mutation was the only independent risk factors to CBC (HR = 7.89, P = .01). CONCLUSION: In this study, BRCA mutation carriers have higher risk of CBC. And, BRCA mutation is the only independent risk factor to CBC. Therefore, intensive surveillance and follow-up as well as more effective individual prevention are urgent. Decisions on alternatively effective prevention, especially the prevention of CBC, are urgent and should take into account patient prognosis and preferences.

KCNN4 induces multiple chemoresistance in breast cancer by regulating BCL2A1.

Multidrug chemoresistance is a major clinical obstacle in breast cancer treatment. We aimed to elucidate the sensitivity to therapeutics in gemcitabine-resistant breast cancer models. Pooled library screening combined with RNA-seq was conducted to explore the potential targets involved in gemcitabine resistance in breast cancer cells. Cytotoxicity and tumor xenograft assays were used to evaluate the effect of calcium-activated channel subfamily N member 4 (KCNN4) inhibitors on the cellular sensitivity of breast cancer cells to chemotherapeutic drugs both in vitro and in vivo. We found that KCNN4 is an important determinant for the cytotoxicity of gemcitabine. Elevated KCNN4 expression enhanced resistance to chemotherapeutic antimetabolites and promoted cell proliferation. Conversely, silencing KCNN4 or chemical inhibition of KCNN4 by the specific inhibitor TRAM-34 inhibited the chemoresistance and cell proliferation. Mechanistically, KCNN4 upregulated BCL2-related protein A1 (BCL2A1) to suppress apoptosis by activating RAS-MAPK and PI3K-AKT signaling. Moreover, high expression levels of KCNN4 and BCL2A1 were associated with shortened disease-free survival in the cohort studies. Collectively, our findings showed that KCNN4 is a key modulator of progression and drug resistance in breast cancer, indicating that targeting KCNN4 may serve as a promising therapeutic strategy to overcome multidrug chemoresistance in this disease.

Insights Into the Impacts of BRCA Mutations on Clinicopathology and Management of Early-Onset Triple-Negative Breast Cancer.

BACKGROUND: Little is known regarding the clinicopathologic characteristics, oncologic outcomes, and treatment strategies that could be ascribed to BRCA mutation in early-onset triple-negative breast cancer (eTNBC). METHODS: eTNBC patients who underwent BRCA genetic testing were derived from our clinical database between 2012 and 2018. Differences in clinical features and pathologic characteristics were examined in groups divided by BRCA mutation status, and the contribution of germline mutations in conjunction with treatment modalities to survival outcomes was determined. RESULTS: Of the 355 qualifying eTNBC patients, 67 (18.87%) were BRCA mutated and 288 (81.13%) were BRCA wild. Overall, median age at diagnosis was 34 years (range, 24-40 years) in the BRCA mutated subgroup and 35 years (range, 21-40 years) in BRCA wild. The majority of clinicopathologic parameters were parallel; however, tumor size (P = 0.07) and nuclear grade (P =0.08) tend to be more aggressive in the BRCA mutated subgroup. Compared with BRCA wild patients, BRCA mutated patients had a higher likelihood of receiving anthracyclines and taxane-based combination chemotherapy (P = 0.04) and tend to be lower tumor burden (P =0.01). After approximately 5-year median follow-up, the overall survival (OS) (P = 0.021) and breast cancer-specific survival (BCSS) (P = 0.004) in BRCA mutated patients were superior to those in their BRCA wild counterparts. Intriguingly, the clinical outcomes were comparable in patients with breast conserving surgery (BCS) regardless of BRCA mutations and in patients with BRCA mutations in spite of surgical schedules. CONCLUSIONS: These results suggest that eTNBC patients with BRCA mutations are prone to better OS and BCSS, which might be largely attributed to more benefit from anthracyclines and taxane-based chemotherapy. The BCS procedure could be a safe alternative surgical option for eTNBC patients with BRCA mutations. Future studies with substantial numbers of participants are urgently needed to validate whether BRCA mutation eTNBC patients are more sensitive to chemotherapy.

Effect of Adjuvant Paclitaxel and Carboplatin on Survival in Women With Triple-Negative Breast Cancer: A Phase 3 Randomized Clinical Trial.

Importance: The value of platinum-based adjuvant chemotherapy in patients with triple-negative breast cancer (TNBC) remains controversial, as does whether BRCA1 and BRCA2 (BRCA1/2) germline variants are associated with platinum treatment sensitivity. Objective: To compare 6 cycles of paclitaxel plus carboplatin (PCb) with a standard-dose regimen of 3 cycles of cyclophosphamide, epirubicin, and fluorouracil followed by 3 cycles of docetaxel (CEF-T). Design, Setting, and Participants: This phase 3 randomized clinical trial was conducted at 9 cancer centers and hospitals in China. Between July 1, 2011, and April 30, 2016, women aged 18 to 70 years with operable TNBC after definitive surgery (having pathologically confirmed regional node-positive disease or node-negative disease with tumor diameter >10 mm) were screened and enrolled. Exclusion criteria included having metastatic or locally advanced disease, having non-TNBC, or receiving preoperative anticancer therapy. Data were analyzed from December 1, 2019, to January 31, 2020, from the intent-to-treat population as prespecified in the protocol. Interventions: Participants were randomized to receive PCb (paclitaxel 80 mg/m2 and carboplatin [area under the curve = 2] on days 1, 8, and 15 every 28 days for 6 cycles) or CEF-T (cyclophosphamide 500 mg/m2, epirubicin 100 mg/m2, and fluorouracil 500 mg/m2 every 3 weeks for 3 cycles followed by docetaxel 100 mg/m2 every 3 weeks for 3 cycles). Main Outcomes and Measures: The primary end point was disease-free survival (DFS). Secondary end points included overall survival, distant DFS, relapse-free survival, DFS in patients with germline variants in BRCA1/2 or homologous recombination repair (HRR)-related genes, and toxicity. Results: A total of 647 patients (mean [SD] age, 51 [44-57] years) with operable TNBC were randomized to receive CEF-T (n = 322) or PCb (n = 325). At a median follow-up of 62 months, DFS time was longer in those assigned to PCb compared with CEF-T (5-year DFS, 86.5% vs 80.3%, hazard ratio [HR] = 0.65; 95% CI, 0.44-0.96; P = .03). Similar outcomes were observed for distant DFS and relapse-free survival. There was no statistically significant difference in overall survival between the groups (HR = 0.71; 95% CI, 0.42-1.22, P = .22). In the exploratory and hypothesis-generating subgroup analyses of PCb vs CEF-T, the HR for DFS was 0.44 (95% CI, 0.15-1.31; P = .14) in patients with the BRCA1/2 variant and 0.39 (95% CI, 0.15-0.99; P = .04) in those with the HRR variant. Safety data were consistent with the known safety profiles of relevant drugs. Conclusions and Relevance: These findings suggest that a paclitaxel-plus-carboplatin regimen is an effective alternative adjuvant chemotherapy choice for patients with operable TNBC. In the era of molecular classification, subsets of TNBC sensitive to PCb should be further investigated. Trial Registration: ClinicalTrials.gov Identifier: NCT01216111.

The Multifunction Of miR-218-5p-Cx43 Axis In Breast Cancer.

BACKGROUND: Gemcitabine is proven to be the first-line standard treatment of breast cancers. Yet, little is known involving gemcitabine resistance and remains largely to be elucidated. MATERIALS AND METHODS: We evaluated the expression of Cx43 in gemcitabine-resistant cells and parental cells by quantitative reverse transcription polymerase chain reaction (qRT-PCR) and Western blot analyses. Dual-luciferase reporter assay was applied to examine the epigenetic regulator of Cx43. The role of miR-218-5p-Cx43 axis on cell cytotoxicity, cell proliferation, colony formation, chemoresistance and migration was detected via mammalian expression vector and small short RNA (shRNA) transfection in vitro. RESULTS: In this study, we found that Cx43 expression levels were significantly lower in gemcitabine-resistant cells than in the parental cells. On deep investigation of the epigenetic regulation of Cx43, a few miRNA candidates targeting Cx43 were derived. Through dual-luciferase reporter assay, Cx43 was proved to be a direct target of miR-218-5p. Besides, qPCR, Western blot demonstrated an inverse correlation between miR-218-5p and Cx43 expression in breast cancer cells, thus forming the miR-218-5p-Cx43 axis. Notably, miR-218-5p-Cx43 axis was found to be involved in the process of gemcitabine chemoresistance, cell proliferation and migration in breast cancer cells. CONCLUSION: Our findings suggested that miR-218-5p-Cx43 axis was versatile and indicated significant potency in breast cancer cells. More importantly, miR-218-5p-Cx43 axis might be valuable in translational medicine, with therapeutic and prognostic information.

Effects of adjuvant chemotherapy in T1N0M0 triple-negative breast cancer.

OBJECTIVES: Patients with T1N0M0 breast cancers are considered to have an excellent prognosis, even in triple-negative breast cancer (TNBC), which is often associated with diminished recurrence-free survival (RFS) and overall survival. Chemotherapy remains the only adjuvant treatment for TNBC, but evidence that adjuvant chemotherapy is beneficial for stage T1N0M0 TNBC patients is limited. In this study, we aimed to evaluate the effect of adjuvant chemotherapy and the benefit of taxanes in T1N0M0 TNBC patients. MATERIAL AND METHODS: A cohort of 354 consecutive patients with newly diagnosed T1N0M0 TNBC between January 2008 and December 2015 were included from the Fudan University Shanghai Cancer Center. Univariate and multivariate survival analyses were performed to compare patients treated with adjuvant chemotherapy with/without taxane addition. RESULTS: Median follow-up was 45 months. Chemotherapy was used in 92.4% of patients. The 5-year estimated RFS rates of patients with and without adjuvant chemotherapy were 94.5% and 83.6%, respectively. In multivariate analysis, adjuvant chemotherapy and a lack of lymphovascular invasion were associated with a significant benefit for RFS. A significant RFS benefit from adjuvant chemotherapy was observed in T1c (hazard ratio, HR = 0.24, 95% CI [0.08-0.76], P = 0.014) but not in T1b (HR = 0.32, 95% CI [0.03-3.18], P = 0.330) subgroups. Addition of taxane to an anthracycline-based regimen was not significantly associated with improved RFS in T1N0M0 TNBC patients. CONCLUSION: Adjuvant chemotherapy improves recurrence-free survival in T1c TNBC patients but not in T1b. Anthracycline-based taxane-free regimens might be sufficient to achieve RFS benefits in T1N0M0 TNBC patients.

Incidence and prognostic factors of patients with synchronous liver metastases upon initial diagnosis of breast cancer: a population-based study.

BACKGROUND: The purpose of this study was to analyze the incidence and prognostic factors of patients with breast cancer liver metastases (BCLM) at initial diagnosis. METHODS: We utilized the Surveillance, Epidemiology, and End Results database to extract data on patients with primary invasive breast cancer from 2010 to 2014. Multivariate logistic regression was conducted to determine factors associated with the presence of liver metastases upon initial diagnosis of breast cancer. Univariate and multivariate Cox regression analyses were performed to identify the prognostic factors in these patients. RESULTS: In total, 3,276 patients with liver metastases were identified upon initial diagnosis of breast cancer. Patients with hormone receptor-negative (HR-), human epidermal growth factor receptor 2-positive (HER2+) breast cancer had the highest incidence (4.6% among the entire population, 46.5% among the metastatic subgroup). Age, gender, race, pathological grade, extrahepatic metastases, tumor subtype, and marital status were identified as factors associated with the presence of liver metastases upon initial diagnosis of breast cancer. The median overall survival among the entire population with BCLM was 20.0 months. Patients with HR+/HER2+ breast cancer had the longest median survival of 36.0 months. The survival analyses indicated that older age, higher pathological grade, extrahepatic metastases, triple-negative subtype, unmarried status, and uninsured status were independent prognostic factors for a poorer prognosis. CONCLUSION: The study provides insight into the incidence and prognostic factors for patients with BCLM at initial diagnosis, which is important clinical information for risk evaluation and prognostic assessment.

Serum miR-4530 sensitizes breast cancer to neoadjuvant chemotherapy by suppressing RUNX2.

PURPOSE: Neoadjuvant chemotherapy (NAC) plays a pivotal role in the treatment of locally advanced breast cancer (LABC); however, breast cancer is a heterogeneous disease, individual responses to chemotherapy are highly variable. Therefore, the purpose of the current research is to identify biomarkers that can predict the chemotherapeutic response. PATIENTS AND METHODS: We recruited 78 patients with primary breast cancer who underwent taxane- and anthracycline-based NAC; these patients were divided into sensitive and resistant groups according to the Response Evaluation Criteria in Solid Tumors (RECIST) criteria. The microRNA microarray was conducted to explore differentially expressed miRNAs. Quantitative real-time polymerase chain reaction (qRT-PCR) further validated the relationship between miR-4530 and chemosensitivity in breast cancer patients. RESULTS: No significant differences were observed between the two groups regarding the clinicopathological characteristics. miR-4530 showed the most potential involving breast cancer chemosensitivity. Mechanically, RUNX2 was identified one of the direct targets of miR-4530 and responsible for breast cancer chemosensitivity. CONCLUSION: Our results revealed that elevated serum miR-4530 levels may sensitize breast cancer to taxane- and anthracycline-based NAC by suppressing RUNX2; therefore, this miRNA has the potential to be a new biomarker for predicting breast cancer chemosensitivity.

The membrane complement regulatory protein CD59 promotes tumor growth and predicts poor prognosis in breast cancer.

Breast cancer is the most prevalent type of cancer among women. CD59, a membrane complement regulatory protein, has been demonstrated to be overexpressed in most solid tumors, where it facilitates tumor cell escape from complement surveillance. However, the role of CD59 in breast cancer growth and clinical prognosis is not fully revealed. To investigate the role of CD59 in breast cancer growth and prognostic significance, we knocked down CD59 in a breast cancer cell line that is highly metastatic to the lungs, MDA-MB­231-HM. Cell growth was measured in vitro and in vivo using a xenograft model. In addition, clinical data on a cohort of 120 patients with or without lung metastasis was analyzed based on CD59 expression, which was detected by immunohistochemistry. Knockdown of CD59 significantly inhibited MDA-MB­231-HM cell growth both in vitro and in vivo. An analysis of clinical data on 120 patients revealed that patients with CD59 overexpression may have a worse prognosis. CD59 may therefore be a prognostic biomarker for poor outcome in breast cancer patients.

Genetic evaluation of BRCA1 associated a complex genes with triple-negative breast cancer susceptibility in Chinese women.

BACKGROUND: The tumor suppressor BRCA1 plays a pivotal role in maintaining genomic stability and tumor suppression. The BRCA1-A complex is required for recruitment of BRCA1 to DNA damage sites, DNA repair and cell cycle checkpoint control. Since germline mutations of BRCA1 often lead to breast tumors that are triple-negative breast cancer (TNBC) type, we aimed to investigate whether genetic deficiency in genes of the BRCA1-A complex is associated with risk to TNBC development. RESULTS: We found that rs7250266 in the promoter region of NBA1 confers a decreased risk to TNBC development, but not to non-TNBC susceptibility. In addition, the haplotypes containing two polymorphisms rs7250266 and rs2278256 are associated with a lower chance of TNBC development specifically. Our studies also showed that the protective alleles of rs7250266 (C > G) and rs2278256 (T > C) down-regulate promoter activity of NBA1 in mammary epithelial cells. METHODS: We investigated associations between the BRCA1-A complex genes and TNBC developing risk in first case-control study of Chinese Han Women population including 414 patients with TNBC and 354 cancer-free controls. We detected 37 common variants in ABRAXAS, RAP80, BRE, BRCC36 and NBA1/MERIT40 genes encoding the BRCA1-A complex and evaluated their genetic susceptibility to the risk of TNBC. An additional cohort with 652 other types of breast cancer (non-TNBC) cases and 890 controls was used to investigate the associations between TNBC-specific SNPs genotype and non-TNBCs susceptibility. CONCLUSIONS: Genetic variants in NBA1 may be an important genetic determinant of TNBC susceptibility. Further investigation and validation of these SNPs in larger cohorts may facilitate in predication and prevention of TNBC and in counseling individuals for risk of TNBC development.

Differences in breast cancer characteristics and outcomes between Caucasian and Chinese women in the US.

Chinese breast cancer patients living in the United States (US) can experience different disease patterns than Caucasians, which might allow for predicting the future epidemiology of breast cancer in China. We aimed to compare the clinicopathologic characteristics and outcomes of Caucasian and Chinese female breast cancer patients residing in the US. The study cohort consisted of 3868 Chinese and 208621 Caucasian women (diagnosed from 1990 to 2009) in the US Surveillance, Epidemiology, and End Results (SEER) database. Compared with the Caucasian patients, the US-residing Chinese patients had a younger age at diagnosis and a higher family income, remained married longer, and more frequently lived in metropolitan areas. Other tumor characteristics were similarly distributed between the two races. Compared with the Caucasians, the Chinese patients had a significantly improved overall survival (OS) but similar breast cancer-specific survival (BCSS). Our analysis suggested that US-residing Chinese patients had significant differences in age, family income, marital status and area of residence, compared with their Caucasian counterparts. No significant disparities were noted in BCSS between the two races, whereas the Chinese patients had a significantly better OS. These findings warrant further investigation and should be considered in the screening and treatment of breast cancer.

A Prospective Evaluation of the Association between a Single Nucleotide Polymorphism rs3775291 in Toll-Like Receptor 3 and Breast Cancer Relapse.

BACKGROUND: Toll-like receptors (TLRs) regulate the balance between the innate and adaptive immune responses. Missense single nucleotide polymorphisms (SNPs) in TLRs might be functional and thus influence the risks of chronic infection and cancer development. Here, we investigated the association of two missense SNPs, rs3775291 (c.1234G>A) in the TLR3 gene and rs4833095 (c.743T>C) in the TLR1 gene, with relapse-free survival (RFS) in a cohort of prospectively observed breast cancer patients. METHODS: In this prospective observational study, rs3775291 in TLR3 and rs4833095 in TLR1 were genotyped in 715 patients with primary breast cancer in a Chinese population. RESULTS: Univariate analysis revealed that the patients with the AA genotype of rs3775291 had a shorter RFS compared with those carrying the G allele in the recessive model (P<0.01), but this finding was not observed with the dominant model (P = 0.31). The results remained significant after adjusting for the clinical parameters in the recessive model (HR = 3.53, 95% confidence interval [CI]: 1.98-6.31, P<0.01). Further survival analysis indicated that this SNP was significant in the luminal-B, triple-negative breast cancer (TNBC), and human epidermal growth factor receptor 2-positive (HER2+) patients using the recessive model but that it was not significant in the luminal-A patients. The SNP rs4833095 showed a non-significant tendency toward an increased RFS rate in the patients with the TT genotype. CONCLUSION: Our results suggest that the SNP rs3775291 in TLR3 may influence patient outcome. Further studies with larger sample sizes should be conducted to validate our findings.

Cytidine Deaminase Axis Modulated by miR-484 Differentially Regulates Cell Proliferation and Chemoresistance in Breast Cancer.

There has been little study of how the evolution of chemoresistance in cancer affects other aspects of disease pathogenesis. Here, we show that an important chemoresistance axis driven by cytidine deaminase (CDA) also acts to suppress cell-cycle progression by regulating cyclin E-CDK2 signaling. We found that CDA was regulated by miR-484 in a gemcitabine-resistant model of breast cancer. Elevating miR-484 expression reversed the CDA effects, thereby enhancing gemcitabine sensitivity, accelerating cell proliferation, and redistributing cell-cycle progression. Conversely, elevating CDA to restore its expression counteracted the chemosensitization and cell proliferative effects of miR-484. In clinical specimens of breast cancer, CDA expression was frequently downregulated and inversely correlated with miR-484 expression. Moreover, high expression of CDA was associated with prolonged disease-free survival in studied cohorts. Collectively, our findings established that miR-484-modulated CDA has a dual impact in promoting chemoresistance and suppressing cell proliferation in breast cancer, illustrating the pathogenic tradeoffs associated with the evolution of chemoresistance in this malignant disease.

Liver kinase B1 enhances chemoresistance to gemcitabine in breast cancer MDA-MB-231 cells.

Liver kinase B1 (LKB1) is a well-known tumor suppressor gene in a variety of human cancers, including breast cancer. However, its role in gemcitabine resistance is unclear. Since gemcitabine in combination with other chemotherapeutic reagents is the first-line treatment in advanced breast cancer, the aim of the present study was to determine the effect of ectopic expression of LKB1 on chemosensitivity to gemcitabine in the breast cancer MDA-MB-231 cell line. Increasing the expression of LKB1 was found to directly correlate with gemcitabine chemoresistance. Although LKB1 suppressed the cell proliferation rate and clonogenicity in the absence of gemcitabine, it increased the median inhibitory concentration of gemcitabine and clonogenicity of cells in the presence of gemcitabine. Mechanistic analysis indicated that LKB1 was able to protect cells from DNA damage caused by gemcitabine. Furthermore, it was found that LKB1 induced a significant upregulation of cytidine deaminase expression, an important enzyme that accelerates gemcitabine catabolization. Overall, dual characteristics of LKB1 were identified: Suppressing cell growth in normal conditions and enhancing chemoresisitance to gemcitabine, possibly by accelerating degradation of gemcitabine, and protecting cells from DNA damage caused by gemcitabine.