Residual Humoral Immunity Sustained Over Decades in a Cohort of Vaccinia-Vaccinated Individuals.

Serological testing of Singaporeans who received childhood smallpox vaccination found anti-vaccinia IgG binding and neutralizing activity indicating long-term humoral immunity. There was correlation between IgG and neutralizing titers indicating IgG could be used as a surrogate marker for humoral immunity. In 2019, Singapore experienced a case of imported monkeypox. As with smallpox, disease can be prevented through vaccination, which was mandatory for Singaporean infants until 1981. However, the degree of residual immunity in older vaccinated Singaporeans remains unknown. Sera from individuals born 1946-1984 were therefore tested and those born prior to 1981 were found to have higher anti-vaccinia IgG and neutralizing activity titers. This suggests that protective humoral immunity remains, which could reduce disease severity in an orthopoxvirus outbreak. Correlation between IgG and neutralizing titers was observed indicating that serology could be used as a surrogate marker for immunity.

Results from a systematic programme of evaluating COVID-19 reinfection cases in the early phase of the pandemic, Singapore.

OBJECTIVES: The objectives of this study were to describe the coronavirus disease caused by SARS-CoV-2 (COVID-19) reinfection evaluation algorithm used in the early phase of the pandemic in Singapore and analyze the clinical and laboratory characteristics of the cases evaluated. METHODS: We performed a retrospective case-control analysis including all COVID-19 cases evaluated for possible reinfection under the local COVID-19 reinfection evaluation programme between 1 June 2020-30 June 2021. Whole genome sequencing (WGS) was used as confirmatory testing. We compared all reinfection ("RI") cases against those who were evaluated but eventually assessed not to be reinfection ("non-RI"). RESULTS: There were 74 possible reinfection cases evaluated through the programme, of which 32 were subsequently classified as RI. There was strong statistical evidence that RI cases had a longer interval between 1st and 2nd episode (mean 297 days; 95%-confidence interval (CI) 267-327) compared to non-RI cases (mean 186 days; 95%-CI 144-228). The cycle threshold (Ct) value of initial polymerase chain rection (PCR) at 2nd episode was also found to be significantly lower in RI cases (mean 23; 95%-CI 20-26) compared to non-RI cases (mean 34; 95%-CI 32-36). There was no significant difference in the proportion of individuals who had fever, acute respiratory symptoms or asymptomatic in both groups. Delta and beta variants were most commonly identified from WGS and provide indication of re-infection as these were not 'wild-type' and were not circulating during the time period of the index infection. CONCLUSIONS: Using a combination of serologic, microbiologic and genomic criteria to evaluate possible reinfection cases is useful and can provide a framework for evaluation that may be modified for future similar situations.

Post-stroke Headache.

PURPOSE OF REVIEW: Stroke is a major health concern and a leading cause of long-term disability. Persistent post-stroke headache (PPSH) is a common complication of stroke yet little is known about its specific characteristics or optimal management. The purpose of this review is to discuss the epidemiology, presentation, and hypothesized pathophysiology of PPSH. Acute and preventive treatment options, as well as specific concerns regarding triptans and the newer CGRP antagonists, will be discussed in detail as well. RECENT FINDINGS: The 2018 International Classification of Headache Disorders, 3rd edition (ICHD-3) was the first headache diagnostic manual to include criteria for PPSH and defines this disorder as an acute headache that develops in close temporal relation to stroke and persists beyond 3 months. Recent literature estimates the prevalence of PPSH to be somewhere between 1 and 23% of patients post-stroke. Presentation is variable, but most often mimics tension-type headache. There are no evidence-based guidelines on the optimal treatment of PPSH. PPSH is a common but poorly understood complication of stroke. Given the significant disability burden that PPSH carries, the epidemiology and pathophysiology of PPSH, as well as the efficacy and safety of potential treatment options, warrant further investigation.

Development and validation of an AI-enabled digital breast cancer assay to predict early-stage breast cancer recurrence within 6 years.

BACKGROUND: Breast cancer (BC) grading plays a critical role in patient management despite the considerable inter- and intra-observer variability, highlighting the need for decision support tools to improve reproducibility and prognostic accuracy for use in clinical practice. The objective was to evaluate the ability of a digital artificial intelligence (AI) assay (PDxBr) to enrich BC grading and improve risk categorization for predicting recurrence. METHODS: In our population-based longitudinal clinical development and validation study, we enrolled 2075 patients from Mount Sinai Hospital with infiltrating ductal carcinoma of the breast. With 3:1 balanced training and validation cohorts, patients were retrospectively followed for a median of 6 years. The main outcome was to validate an automated BC phenotyping system combined with clinical features to produce a binomial risk score predicting BC recurrence at diagnosis. RESULTS: The PDxBr training model (n = 1559 patients) had a C-index of 0.78 (95% CI, 0.76-0.81) versus clinical 0.71 (95% CI, 0.67-0.74) and image feature models 0.72 (95% CI, 0.70-0.74). A risk score of 58 (scale 0-100) stratified patients as low or high risk, hazard ratio (HR) 5.5 (95% CI 4.19-7.2, p < 0.001), with a sensitivity 0.71, specificity 0.77, NPV 0.95, and PPV 0.32 for predicting BC recurrence within 6 years. In the validation cohort (n = 516), the C-index was 0.75 (95% CI, 0.72-0.79) versus clinical 0.71 (95% CI 0.66-0.75) versus image feature models 0.67 (95% CI, 0.63-071). The validation cohort had an HR of 4.4 (95% CI 2.7-7.1, p < 0.001), sensitivity of 0.60, specificity 0.77, NPV 0.94, and PPV 0.24 for predicting BC recurrence within 6 years. PDxBr also improved Oncotype Recurrence Score (RS) performance: RS 31 cutoff, C-index of 0.36 (95% CI 0.26-0.45), sensitivity 37%, specificity 48%, HR 0.48, p = 0.04 versus Oncotype RS plus AI-grade C-index 0.72 (95% CI 0.67-0.79), sensitivity 78%, specificity 49%, HR 4.6, p < 0.001 versus Oncotype RS plus PDxBr, C-index 0.76 (95% CI 0.70-0.82), sensitivity 67%, specificity 80%, HR 6.1, p < 0.001. CONCLUSIONS: PDxBr is a digital BC test combining automated AI-BC prognostic grade with clinical-pathologic features to predict the risk of early-stage BC recurrence. With future validation studies, we anticipate the PDxBr model will enrich current gene expression assays and enhance treatment decision-making.

Epidemiological and Clinical Predictors of COVID-19.

BACKGROUND: Rapid identification of COVID-19 cases, which is crucial to outbreak containment efforts, is challenging due to the lack of pathognomonic symptoms and in settings with limited capacity for specialized nucleic acid-based reverse transcription polymerase chain reaction (PCR) testing. METHODS: This retrospective case-control study involves subjects (7-98 years) presenting at the designated national outbreak screening center and tertiary care hospital in Singapore for SARS-CoV-2 testing from 26 January to 16 February 2020. COVID-19 status was confirmed by PCR testing of sputum, nasopharyngeal swabs, or throat swabs. Demographic, clinical, laboratory, and exposure-risk variables ascertainable at presentation were analyzed to develop an algorithm for estimating the risk of COVID-19. Model development used Akaike's information criterion in a stepwise fashion to build logistic regression models, which were then translated into prediction scores. Performance was measured using receiver operating characteristic curves, adjusting for overconfidence using leave-one-out cross-validation. RESULTS: The study population included 788 subjects, of whom 54 (6.9%) were SARS-CoV-2 positive and 734 (93.1%) were SARS-CoV-2 negative. The median age was 34 years, and 407 (51.7%) were female. Using leave-one-out cross-validation, all the models incorporating clinical tests (models 1, 2, and 3) performed well with areas under the receiver operating characteristic curve (AUCs) of 0.91, 0.88, and 0.88, respectively. In comparison, model 4 had an AUC of 0.65. CONCLUSIONS: Rapidly ascertainable clinical and laboratory data could identify individuals at high risk of COVID-19 and enable prioritization of PCR testing and containment efforts. Basic laboratory test results were crucial to prediction models.

Oral vs Intravenous Antibiotics for Patients With Klebsiella pneumoniae Liver Abscess: A Randomized, Controlled Noninferiority Study.

BACKGROUND: Klebsiella pneumoniae liver abscess (KLA) is emerging worldwide due to hypermucoviscous strains with a propensity for metastatic infection. Treatment includes drainage and prolonged intravenous antibiotics. We aimed to determine whether oral antibiotics were noninferior to continued intravenous antibiotics for KLA. METHODS: This noninferiority, parallel group, randomized, clinical trial recruited hospitalized adults with liver abscess and K. pneumoniae isolated from blood or abscess fluid who had received ≤7 days of effective antibiotics at 3 sites in Singapore. Patients were randomized 1:1 to oral (ciprofloxacin) or intravenous (ceftriaxone) antibiotics for 28 days. If day 28 clinical response criteria were not met, further oral antibiotics were prescribed until clinical response was met. The primary endpoint was clinical cure assessed at week 12 and included a composite of absence of fever in the preceding week, C-reactive protein <20 mg/L, and reduction in abscess size. A noninferiority margin of 12% was used. RESULTS: Between November 2013 and October 2017, 152 patients (mean age, 58.7 years; 25.7% women) were recruited, following a median 5 days of effective intravenous antibiotics. A total of 106 (69.7%) underwent abscess drainage; 71/74 (95.9%) randomized to oral antibiotics met the primary endpoint compared with 72/78 (92.3%) randomized to intravenous antibiotics (risk difference, 3.6%; 2-sided 95% confidence interval, -4.9% to 12.8%). Effects were consistent in the per-protocol population. Nonfatal serious adverse events occurred in 12/72 (16.7%) in the oral group and 13/77 (16.9%) in the intravenous group. CONCLUSIONS: Oral antibiotics were noninferior to intravenous antibiotics for the early treatment of KLA. CLINICAL TRIALS REGISTRATION: NCT01723150.

Imported Monkeypox, Singapore.

In May 2019, we investigated monkeypox in a traveler from Nigeria to Singapore. The public health response included rapid identification of contacts, use of quarantine, and postexposure smallpox vaccination. No secondary cases were identified. Countries should develop surveillance systems to detect emerging infectious diseases globally.

Epidemiologic Features and Clinical Course of Patients Infected With SARS-CoV-2 in Singapore.

Importance: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged in Wuhan, China, in December 2019 and has spread globally with sustained human-to-human transmission outside China. Objective: To report the initial experience in Singapore with the epidemiologic investigation of this outbreak, clinical features, and management. Design, Setting, and Participants: Descriptive case series of the first 18 patients diagnosed with polymerase chain reaction (PCR)-confirmed SARS-CoV-2 infection at 4 hospitals in Singapore from January 23 to February 3, 2020; final follow-up date was February 25, 2020. Exposures: Confirmed SARS-CoV-2 infection. Main Outcomes and Measures: Clinical, laboratory, and radiologic data were collected, including PCR cycle threshold values from nasopharyngeal swabs and viral shedding in blood, urine, and stool. Clinical course was summarized, including requirement for supplemental oxygen and intensive care and use of empirical treatment with lopinavir-ritonavir. Results: Among the 18 hospitalized patients with PCR-confirmed SARS-CoV-2 infection (median age, 47 years; 9 [50%] women), clinical presentation was an upper respiratory tract infection in 12 (67%), and viral shedding from the nasopharynx was prolonged for 7 days or longer among 15 (83%). Six individuals (33%) required supplemental oxygen; of these, 2 required intensive care. There were no deaths. Virus was detectable in the stool (4/8 [50%]) and blood (1/12 [8%]) by PCR but not in urine. Five individuals requiring supplemental oxygen were treated with lopinavir-ritonavir. For 3 of the 5 patients, fever resolved and supplemental oxygen requirement was reduced within 3 days, whereas 2 deteriorated with progressive respiratory failure. Four of the 5 patients treated with lopinavir-ritonavir developed nausea, vomiting, and/or diarrhea, and 3 developed abnormal liver function test results. Conclusions and Relevance: Among the first 18 patients diagnosed with SARS-CoV-2 infection in Singapore, clinical presentation was frequently a mild respiratory tract infection. Some patients required supplemental oxygen and had variable clinical outcomes following treatment with an antiretroviral agent.

Identification of a Carbapenemase-Producing Hypervirulent Klebsiella pneumoniae Isolate in the United States.

We report on a carbapenemase-producing hypervirulent Klebsiella pneumoniae (CP-hvKP) isolate collected from a U.S. patient at an outpatient clinic. The isolate was identified as K. pneumoniae serotype K1 sequence type 23 and included both a hypervirulence (with rmpA, rmpA2 iroBCDN, peg-344, and iucABCD-iutA genes) and a carbapenemase-encoding (blaKPC-2) plasmid. The emergence of CP-hvKP underscores the importance of clinical awareness of this pathotype and the need for continued monitoring of CP-hvKP in the United States.

Characterisation of bone and joint infections due to Group B Streptococcus serotype III sequence type 283.

In 2015, an epidemic of Group B Streptococcus (GBS) serotype III sequence type 283 (ST283) disease was reported in Singapore, associated with consumption of raw freshwater fish. In this study, we further characterise the characteristics of bone and joint infections associated with ST283 GBS in adults and the differences between ST283 and non-ST283 manifestations. A retrospective study of 54 inpatients with invasive GBS disease involving bones and/or joints from 2010 to 2015 was performed. Archived isolates were identified as GBS serotype III and ST283 positive using PCR methods. Clinical data were collected from a review of clinical charts. Twenty-three cases were ST283 and 31 were non-ST283. ST283 GBS patients were more likely to be of Chinese ethnicity, have lower Charlson comorbidity scores, and have fewer overall comorbidities, including diabetes mellitus with end-organ damage, peripheral vascular disease, and previous stroke, compared to non-ST283 GBS patients. ST283 patients had more oligoarthritis, with greater involvement of the knee, shoulder, and vertebrae, compared to monoarticular joint involvement in non-ST283 patients. Six patients had a unique combination of knee and shoulder joint involvement. All ST283 cases were mono-microbial, compared to a significant proportion of polymicrobial cultures in non-ST283 patients. Non-ST283 patients had a significantly longer length of stay and were more likely to undergo amputation or wound debridement. This study adds to growing evidence of a distinct clinical presentation associated with ST283 GBS, involving predominantly healthier patients without significant comorbidities, and with distinct clinical manifestations with regard to bone and joint disease.

Outpatient parenteral antibiotic therapy (OPAT) in Asia: missing an opportunity.

Objectives: Healthcare facilities internationally have grown outpatient parenteral antibiotic administration services for the last few decades. The literature contains publications from dozens of countries describing systematized processes with specialist oversight and their levels of service provision and outcomes. Such descriptions are absent in the majority of Asian countries. We sought to elucidate the extent and nature of outpatient parenteral antibiotic therapy (OPAT) in Asia and to consider the ramifications and opportunities for improvement. Methods: Utilizing colleagues and their personal networks, we surveyed healthcare facilities across 17 countries in Asia to ascertain the current means (if any) of providing OPAT. In that survey we also sought to explore the capacity and interest of these facilities in developing systematized OPAT services. Results: Responses were received from 171 different healthcare facilities from 17 countries. Most (97/171, 57%) stated that they administer outpatient parenteral antibiotics, but only 5 of 162 facilities (3%) outside of Singapore described comprehensive services with specialist oversight. Conclusions: There is very likely a large unrecognized problem of unchecked outpatient parenteral antibiotic administration in Asia. Developing comprehensive and systematized OPAT in Asia is needed as a priority in an environment in which the infectious diseases community is demanding broad stewardship approaches. There are nonetheless challenges in establishing and sustaining OPAT programmes. Local champions and leverage off identified local incentives and needs are key to regional advancement.

Role of outpatient parenteral antibiotic therapy in the treatment of community acquired skin and soft tissue infections in Singapore.

BACKGROUND: Treatment of community acquired skin and soft tissue infections (SSTIs) is a common indication for outpatient parenteral antibiotic therapy (OPAT) in USA, UK and Australasia, however data from Asia are lacking. OPAT is well established within the Singapore healthcare since 2002, however, systematic use of OPAT for the treatment of SSTIs remains infrequent. In this report, we describe the treatment and outcome of patients with SSTIs referred directly from Emergency Department (ED) to OPAT for continuation of intravenous (IV) antibiotics in Singapore, thus avoiding potential hospital admission. METHOD: This is a single center university hospital retrospective study of patients with SSTIs presenting to ED who were assessed to require IV antibiotics and accepted to the OPAT clinic for continuation of IV treatment. Exclusion criteria were: haemodynamic instability, uncontrolled or serious underlying co-morbidities, necessity for inpatient surgical drainage, facial cellulitis and cephalosporin allergy. Patients returned daily to the hospital's OPAT clinic for administration of IV antibiotics and review, then switched to oral antibiotics on improvement. RESULTS: From 7 February 2012 to 31 July 2015, 120 patients with SSTIs were treated in OPAT. Median age was 56 years and 63% were male. Lower limbs were affected in 91%. Diabetes was present in 20%. Sixty-seven (56%) had been treated with oral antibiotics for a median duration of 3 days prior to OPAT treatment. Common symptoms were erythema (100%), swelling (96%), pain (88%) and fever (55%). Antibiotics administered were IV cefazolin with oral probenecid (71%) or IV ceftriaxone (29%) for median 3 days then oral cloxacillin (85%) for median 7 days. Clinical improvement occurred in 90%. Twelve patients (10%) were hospitalized for worsening cellulitis, with 4 patients requiring surgical drainage of abscess. Microbiological cultures from 2 patients with drained abscess grew methicillin sensitive Staphylococcus aureus (MSSA) and Klebsiella pneumoniae, both of which were susceptible to cefazolin and ceftriaxone. Hospital bed days saved was 318 days. CONCLUSION: OPAT treatment of community acquired SSTIs in a selected patient population has good outcomes in Singapore. Treatment with IV cefazolin or IV ceftriaxone was successful in the majority with low hospital readmission rate.

Prognostic significance of proline, glutamic acid, leucine rich protein 1 (PELP1) in triple-negative breast cancer: a retrospective study on 129 cases.

BACKGROUND: Triple-negative breast cancer (TNBC) is associated with an aggressive clinical course due to the lack of therapeutic targets. Therefore, identifying reliable prognostic biomarkers and novel therapeutic targets for patients with TNBC is required. Proline, glutamic acid, leucine rich protein 1 (PELP1) is a novel steroidal receptor co-regulator, functioning as an oncogene and its expression is maintained in estrogen receptor (ER) negative breast cancers. PELP1 has been proposed as a prognostic biomarker in hormone-related cancers, including luminal-type breast cancers, but its significance in TNBC has not been studied. METHODS: PELP1 immunoreactivity was evaluated using immunohistochemistry in 129 patients with TNBC. Results were correlated with clinicopathological variables including patient's age, tumor size, lymph node stage, tumor grade, clinical stage, histological type, Ki-67 LI, as well as clinical outcome of the patients, including disease-free survival (DFS) and overall survival (OS). RESULTS: PELP1 was localized predominantly in the nuclei of carcinoma cells in TNBC. With the exception of a positive correlation between PELP1 protein expression and lymph node stage (p = 0.027), no significant associations between PELP1 protein expression and other clinicopathological variables, including DFS and OS, were found. However, when PELP1 and Ki-67 LI were grouped together, we found that patients in the PELP1/Ki-67 double high group (n = 48) demonstrated significantly reduced DFS (p = 0.005, log rank test) and OS (p = 0.002, log rank test) than others (n = 81). Multivariable analysis supported PELP1/Ki-67 double high expression as an independent prognostic factor in patients with TNBC, with an adjusted hazard ratio of 2.020 for recurrence (95 % CL, 1.022-3.990; p = 0.043) and of 2.380 for death (95 % CL, 1.138-4.978; p = 0.021). CONCLUSIONS: We found that evaluating both PELP1 and Ki-67 expression in TNBC could enhance the prognostic sensitivity of the two biomarkers. Therefore, we propose that PELP1/Ki-67 double high expression in tumors is an independent prognostic factor for predicting a poor outcome for patients with TNBC.

High prevalence of non-alcoholic fatty liver disease in the Chinese - results from the Hong Kong liver health census.

BACKGROUND & AIMS: The prevalence of non-alcoholic fatty liver disease (NAFLD) in the general Chinese population is not clear, as there have been few large population studies focussing on healthy individuals. We aim to determine the prevalence and risk factors of NAFLD in a healthy Westernized Chinese population. METHODS: This is a prospective cross-sectional study of 2493 volunteers recruited from the general population and the Red Cross Transfusion Center in Hong Kong. All underwent comprehensive questionnaire survey, blood test, abdominal ultrasound and transient elastography. RESULTS: The prevalence of NAFLD was 42%. Gender, age, waist circumference, systolic blood pressure, fasting cholesterol and glucose levels were significant factors. The relative risk of NAFLD in those with high waist circumference, diabetes, hypertension, and hypercholesterolaemia was 2.99, 2.01, 1.79 and 1.54 respectively. The degree of steatosis increased with levels of fasting glucose, cholesterol, systolic blood pressure and waist circumference (all P < 0.001). The optimal waist circumference was found to be 84 and 74 cm for male and females respectively, with a relative risk of 5.16 for those above this limit. In total, 1.2% and 0.002% with NAFLD had advanced liver fibrosis and cirrhosis respectively. CONCLUSION: Non-alcoholic fatty liver disease was found to be highly prevalent in the Chinese population. Increasing levels of risk factors were associated with increasing severity of NAFLD. Lower cut-off levels of waist circumference to predict NAFLD should be adopted for Chinese population.

Tumor-infiltrating CD8+ and FOXP3+ lymphocytes in triple-negative breast cancer: its correlation with pathological complete response to neoadjuvant chemotherapy.

The anti-tumor immune response was recently reported to play a critical role in the chemotherapeutic sensitivity of breast cancer. Therefore, we investigated the correlation between CD8+ and FOXP3+ tumor-infiltrating lymphocytes and the pathological complete response (pCR) following neoadjuvant chemotherapy (NAC) in triple-negative breast cancer (TNBC), in conjunction with neoangiogenesis, basal and proliferation markers. CD8+ and FOXP3+ lymphocytes were assessed in biopsy specimens by double-staining immunohistochemistry, in combination with immunostaining of vasohibin-1, CD31, EGFR, CK5/6, and Ki-67. Earlier age, pre-menopausal status, smaller tumor size, and high Ki-67 were significantly associated with pCR, as in high CD8+, high CD8+/FOXP3+ ratio, and low vasohibin-1 positive ratio. Multivariate analysis did reveal that a high CD8+/FOXP3+ ratio was a strong predictor of pCR with an odds ratio of 5.32 (P = 0.005). High Ki-67 was also significantly associated with pCR (P = 0.002). TNBCs with a high CD8+/FOXP3+ ratio and high Ki-67 had the highest pCR rate (70%) following NAC. However, the pCR rate of the patients with low CD8+/FOXP3+ ratio and low Ki-67 was only 5%. The pCR rates of a high CD8+/FOXP3+ ratio and low Ki-67 patients and those with a low CD8+/FOXP3+ ratio and high Ki-67 were 24 and 21%, respectively. TNBCs with a high CD8+/FOXP3+ ratio were more sensitive to anthracycline and taxane-based chemotherapeutic regimens, and the CD8+/FOXP3+ ratio in conjunction with Ki-67 could predict pCR following NAC in TNBC. This predictor may represent a new surrogate for testing the efficacy of investigational agents in the neoadjuvant setting.

Predictors of mortality in culture-proven Burkholderia pseudomallei infections in a Singapore Tertiary Hospital.

Burkholderia pseudomallei is a pathogen expanding in geographic range. We performed a retrospective study analyzing the clinical, microbiologic features of culture-proven melioidosis, and predictors of mortality based on data from a Singapore tertiary hospital between 2006- 2016. We found ICU admission, bacteremia, and mechanical ventilation to be associated with mortality.

Aromatase inhibitor treatment of breast cancer cells increases the expression of let-7f, a microRNA targeting CYP19A1.

Aromatase inhibitors (AIs) are considered the gold standard of endocrine therapy for oestrogen receptor-positive postmenopausal breast cancer patients. AI treatment was reported to result in marked alterations of genetic profiles in cancer tissues but its detailed molecular mechanisms have not been elucidated. Therefore, we profiled miRNA expression before and after treatment with letrozole in MCF-7 co-cultured with primary breast cancer stromal cells. Letrozole significantly altered the expression profiles of cancer miRNAs in vitro. Among the elevated miRNAs following letrozole treatment, computational analysis identified let-7f, a tumour-suppressor miRNA which targeted the aromatase gene (CYP19A1) expression. Quantitative real-time PCR assay using MCF-7 and SK-BR-3 cells as well as clinical specimens of a neoadjuvant study demonstrated a significant inverse correlation between aromatase mRNA and let-7f expression. In addition, high let-7f expression was significantly correlated with low aromatase protein levels evaluated by both immunohistochemistry and the western blotting method in breast cancer cases. Results of 3'UTR luciferase assay also demonstrated the actual let-7f binding sites in CYP19A1, indicating that let-7f directly targets the aromatase gene. Subsequent WST-8 and migration assays performed in let-7f-transfected MCF-7 and SK-BR-3 cells revealed a significant decrement of their proliferation and migration. These findings all demonstrated that let-7f, a tumour suppressor miRNA in breast cancer, directly targeted the aromatase gene and was restored by AI treatment. Therefore, AIs may exert tumour-suppressing effects upon breast cancer cells by suppressing aromatase gene expression via restoration of let-7f.