Demographics and Clinical Decision Making in Patients with Germline Moderate Penetrance Non-BRCA Mutations in Breast Cancer Related Genes.

BACKGROUND: Management of pathogenic variants in high penetrance genes related to breast cancer (BC), such as BRCA1 and BRCA2, are well established. However, moderate penetrance mutations are understudied. We aim to compare risk reduction decision-making patterns in patients with a moderate penetrance BC-related genetic mutations, without a prior BC diagnosis. PATIENTS AND METHODS: Female patients aged ≥ 18 years who tested positive for a BRCA1/2, high penetrance, or moderate penetrance mutation related to BC between 1996 and 2023 without a concurrent or prior BC diagnosis were retrospectively identified from a single academic center's database. Groups were stratified by mutation type: BRCA1/2 mutations (BRCA1, BRCA2), high penetrance mutations (HPM; CDH1, PALB2, PTEN, STK11, TP53), or moderate penetrance mutations (MPM; ATM, BARD1, CHEK2, NF1, RAD51C, RAD51D). Demographics and clinical outcomes were compared. RESULTS: A total of 528 patients met the inclusion criteria, with 66% (n = 350) having a BRCA1/2 mutation, 8% (n = 44) having HPM, and 25% (n = 134) having MPM; the median follow-up was 56.0 months. In our cohort, 20.9% of patients with BRCA mutations, 9.1% with HPM, and 7.5% with MPM chose to undergo risk-reducing mastectomies (RRM). Within the moderate penetrance cohort, patients who chose to undergo RRM were younger at the time of genetic testing (39.4 vs. 47.5 years, p = 0.03) and had a higher number of family members with BC (2 vs. 1, p = 0.05). CONCLUSIONS: Our findings provide insights into the demographic characteristics and family history of patients with moderate penetrance mutations and those who pursue risk-reducing surgery.

Trajectory of Subsequent Breast Cancer Diagnoses in a Diverse Patient Cohort with Breast Atypia.

BACKGROUND: Proliferative breast atypical lesions, including atypical ductal hyperplasia (ADH) and lobular intraepithelial neoplasms (LIN), represent benign entities that confer an elevated risk of ductal carcinoma in situ (DCIS) and invasive breast cancer (IBC). However, the timing of disease progression is variable and risk factors associated with the trajectory of disease are unknown. METHODS: Patients diagnosed with ADH or LIN from 1992 to 2017 at an academic center were identified. Early progression was defined as DCIS or IBC diagnosed within 5 years following the initial atypia diagnosis. Unadjusted cancer-free survival was estimated using the Kaplan-Meier method. Demographics, clinicopathologic features, and use of chemoprevention were compared between the early and late development groups. RESULTS: Overall, 418 patients were included-73.7% with ADH and 26.3% with LIN. Over a median follow up of 92.1 months, 71/418 (17.0%) patients developed IBC (57.7%) or DCIS (42.3%). Almost half (47.9%, 34/71) were diagnosed within 5 years of their initial atypia diagnosis, and 52.1% (37/71) were diagnosed after 5 years. Patient and atypia characteristics were not associated with rate of events or time to events. There was a trend of early events being more often ipsilateral (76.5% early vs. 54.1% late; p = 0.13) versus contralateral. CONCLUSIONS: In a large cohort of patients with breast atypia and long-term follow up, 17% experienced subsequent breast events, with approximately half of the events occurring within the first 5 years following the initial atypia diagnosis. Clinical features were not associated with the trajectory to subsequent events, supporting that atypia signals both local and overall malignancy risk.

Triple-Negative Breast Cancer in Older Patients: Does SLNB Guide Therapy?

BACKGROUND: Older breast cancer patients represent a heterogeneous population. Studies demonstrate that sentinel lymph node biopsy (SLNB) omission may be appropriate in some clinical scenarios, yet patients with triple-negative breast cancer (TNBC) are often excluded from these studies. This study evaluated differences in treatment and survival for older patients with TNBC based on SLNB receipt and result. METHODS: Patients 70 years old or older with a diagnosis of cT1-2/cN0/M0 TNBC (2010-2019) who underwent surgery were selected from the National Cancer Database. Logistic regression estimated the association of SLNB with therapy, and Cox proportional hazards models estimated the association of SLNB with overall survival (OS) after adjustment for select factors. RESULTS: Of the 15,167 patients included in the study (median age, 77 years), 13.02% did not undergo SLNB, 5.14% had pN1 disease, 0.12% had pN2 disease, and 0.01% had pN3 disease. Most of the patients (83.9%) underwent surgery first, and 16.1% received neoadjuvant chemotherapy. Of those who underwent surgery first and SLNB, 6.2% had pN+ disease. Receipt of SLNB was associated with a higher likelihood of chemotherapy (odds ratio [OR] 1.85; 95% confidence interval [CI] 1.55-2.21), regardless of pN status. Compared with those who did not undergo a SLNB, a negative SLNB was significantly associated with lower mortality (hazard ratio [HR] 0.68; 95% CI 0.63-0.75), although there was no difference for a positive SLNB (HR 1.14; 95% CI 0.98-1.34). The patients receiving chemotherapy first showed no difference in survival based on SLNB receipt or result (p = 0.23). CONCLUSIONS: Most older patients with TNBC do not have nodal involvement and do not receive chemotherapy. The receipt and results of SLNB may be associated with outcomes for some who undergo surgery first, but not for those who receive neoadjuvant chemotherapy.

Omission of Axillary Lymph Node Dissection in Patients with Residual Nodal Disease After Neoadjuvant Chemotherapy.

BACKGROUND: Axillary management after neoadjuvant chemotherapy (NAC) is evolving but axillary lymph node dissection (ALND) remains the standard of care for patients with residual nodal disease. The results of the Alliance A011202 trial evaluating the oncologic safety of ALND omission in this cohort are pending but we hypothesize that ALND omission is already increasing. METHODS: The National Cancer Database was queried to identify patients diagnosed with cT1-3N1M0 breast cancer who underwent NAC and had residual nodal disease (ypN1mi-2) from 2012 to 2021. Temporal trends in omission of completion ALND were assessed annually. Multivariable logistic and Cox regression models were used to identify factors associated with ALND omission and overall survival (OS), respectively. RESULTS: A total of 6101 patients were included; the majority presented with cT2 disease (57%), with 69% HER2+, 23% triple-negative, and 8% hormone receptor-positive/HER2-. Overall, 34% underwent sentinel lymph node biopsy (SLNB) alone. Rates of ALND were the lowest in the last 4 years of observation. After adjustment, treatment at community centers (vs. academic) and lower pathologic nodal burden were associated with omission of ALND. ALND omission was associated with a higher unadjusted OS (5-year OS: 86% SLNB alone vs. 84% ALND; log-rank p = 0.03), however this association was not maintained after adjustment. CONCLUSIONS: Despite the impending release of the Alliance A011202 results, omission of ALND in patients with residual nodal disease after NAC is increasing. This practice appears more prominent in community centers and in patients with a lower burden of residual nodal disease. No association with OS was noted.

Rates of Pathologic Complete Response and Overall Survival in Patients with Inflammatory Breast Cancer: A National Cancer Database Study.

BACKGROUND: Patients with inflammatory breast cancer (IBC) have worse survival compared with stage III non-IBC matched cohorts; however, the prognostic significance of achieving pathologic complete response (pCR) in the setting of IBC is not well described. We evaluated overall survival (OS) between IBC patients and non-IBC patients who achieved pCR. METHODS: Adult females diagnosed in 2010-2018 with clinical prognostic stage III unilateral invasive breast cancer treated with neoadjuvant chemotherapy (NAC) followed by surgery were selected from the National Cancer Database. Unadjusted OS from surgery was estimated using the Kaplan-Meier method, and log-rank tests were used to compare groups. Cox proportional hazard models were used to estimate the association of study groups with OS after adjustment for available covariates. RESULTS: The study included 38,390 patients; n = 4600 (12.0%) IBC and n = 33,790 (88.0%) non-IBC. Overall pCR rates were lower for IBC compared with non-IBC (20.7% vs. 23.3%; p < 0.001). Among those achieving pCR, 5-year mortality was higher for IBC patients (16.4%, 95% confidence interval [CI] 13.9-19.1%) versus non-IBC patients (9.1%, 95% CI 8.4-9.8%; log-rank p < 0.001). Among all patients achieving pCR, IBC remained associated with worse OS compared with non-IBC (hazard ratio 1.48, 95% CI 1.19-1.85; p < 0.001). CONCLUSION: We found a lower pCR rate and worse OS in IBC patients compared with non-IBC stage III patients. Despite effective systemic therapies, achieving a pCR for IBC patients may not carry the same prognostic impact compared with non-IBC stage III patients.

The Top Ten Annals of Surgical Oncology Original Articles on Twitter/X: 2020-2023.

Social media has become omnipresent in society, especially given that it enables the rapid and widespread communication of news, events, and information. Social media platforms have become increasingly used by numerous surgical societies to promote meetings and surgical journals to increase the visibility of published content. In September 2020, Annals of Surgical Oncology (ASO) established its Social Media Committee (SMC), which has worked to steadily increase the visibility of published content on social media platforms, namely X (formerly known as Twitter). The purpose of this review is to highlight the 10 ASO original articles with the most engagement on X, based on total number of mentions, since the founding of the SMC. These articles encompass a wide variety of topics from various oncologic disciplines including hepatopancreatobiliary, breast, and gynecologic surgery.

Assessment of Treatment Sequence in Patients With Stage III Breast Cancer.

INTRODUCTION: Stage III breast cancer is defined as locally advanced breast cancer and is treated with curative intent. Historically, overall survival (OS) did not differ based on treatment sequence (neoadjuvant chemotherapy [NAC] followed by surgery versus surgery followed by chemotherapy). Given recent advancements, we examined if treatment sequence may be associated with improved OS in a contemporary cohort of patients with stage III breast cancer. METHODS: Patients aged 18-80 years with prognostic stage III breast cancer who received chemotherapy and surgery were selected from the Surveillance, Epidemiology, and End Results database. Patients were stratified by treatment sequence (NAC versus surgery first). Unadjusted OS and breast cancer-specific survival (BCSS) were estimated using the Kaplan-Meier method and compared with log-rank tests. Cox proportional hazards models were used to estimate the association of treatment sequence with OS and BCSS after adjustment for selected covariates. RESULTS: The study included 26,573 patients; median follow-up was 62.0 months (95% confidence interval [CI] 61.0-63.0). Patients receiving NAC had a worse OS and BCSS compared to those who underwent surgery first (5-year OS rates 0.66 versus 0.73; 5-year BCSS rates 0.70 versus 0.77; both log-rank P < 0.001). After adjustment for tumor subtype, receipt of NAC (versus surgery first) remained associated with a worse OS (hazard ratio 1.27, 95% CI 1.2-1.34, P < 0.001) and BCSS (hazard ratio 1.35, 95% CI 1.27-1.43, P < 0.001). CONCLUSIONS: Based on data from patients treated largely before 2020, undergoing surgery first may be associated with improved survival, even after adjustment for known covariates including tumor subtype. These findings may inform treatment when caring for patients with operable, locally advanced breast cancer.

Anatomy Versus Biology: What Guides Chemotherapy Decisions in Older Patients With Breast Cancer?

INTRODUCTION: With the increasing utilization of genomic assays, such as the Oncotype DX recurrence score (RS), the relevance of anatomic staging has been questioned for select older patients with breast cancer. We sought to evaluate differences in chemotherapy receipt and/or survival among older patients based on RS and sentinel lymph node biopsy (SLNB) receipt/result. METHODS: Patients aged ≥ 65 diagnosed with pT1-2/cN0/M0 hormone-receptor-positive (HR+)/HER2-breast cancer (2010-2019) were selected from the National Cancer Database. Logistic regression was used to identify factors associated with chemotherapy receipt. Cox proportional hazards models were used to estimate the association of RS/SLNB group with overall survival. A cost-benefit study was also performed. RESULTS: Of the 75,428 patients included, the majority had an intermediate RS (58.2% versus 27.9% low, 13.8% high) and were SLNB- (85.1% versus 11.6% SLNB+, 3.3% none). Chemotherapy was recommended for 13,442 patients (17.8%). After adjustment, chemotherapy receipt was more likely with higher RS and SLNB+. After adjustment, SLNB receipt/result was only associated with overall survival among those with an intermediate RS. However, returning to the OR for SLNB is not cost-effective. CONCLUSIONS: SLNB receipt/result was associated with survival for those with an intermediate RS, but not a low or high RS, suggesting that an SLNB may indeed be unnecessary for select older patients with breast cancer.

Breast Conservation Surgery and Mastectomy Have Similar Locoregional Recurrence After Neoadjuvant Chemotherapy: Results From 1462 Patients on the Prospective, Randomized I-SPY2 Trial.

Neoadjuvant chemotherapy (NAC) increases rates of successful breast-conserving surgery (BCS) in patients with breast cancer. However, some studies suggest that BCS after NAC may confer an increased risk of locoregional recurrence (LRR). We assessed LRR rates and locoregional recurrence-free survival (LRFS) in patients enrolled on I-SPY2 (NCT01042379), a prospective NAC trial for patients with clinical stage II to III, molecularly high-risk breast cancer. Cox proportional hazards models were used to evaluate associations between surgical procedure (BCS vs mastectomy) and LRFS adjusted for age, tumor receptor subtype, clinical T category, clinical nodal status, and residual cancer burden (RCB). In 1462 patients, surgical procedure was not associated with LRR or LRFS on either univariate or multivariate analysis. The unadjusted incidence of LRR was 5.4% after BCS and 7.0% after mastectomy, at a median follow-up time of 3.5 years. The strongest predictor of LRR was RCB class, with each increasing RCB class having a significantly higher hazard ratio for LRR compared with RCB 0 on multivariate analysis. Triple-negative receptor subtype was also associated with an increased risk of LRR (hazard ratio: 2.91, 95% CI: 1.8-4.6, P < 0.0001), regardless of the type of operation. In this large multi-institutional prospective trial of patients completing NAC, we found no increased risk of LRR or differences in LRFS after BCS compared with mastectomy. Tumor receptor subtype and extent of residual disease after NAC were significantly associated with recurrence. These data demonstrate that BCS can be an excellent surgical option after NAC for appropriately selected patients.

Does Preoperative MRI Reduce Positive Margins after Breast-Conserving Surgery?

BACKGROUND: Breast-conserving surgery (BCS) is a mainstay for breast cancer management, and obtaining negative margins is critical. Some have advocated for the use of preoperative magnetic resonance imaging (MRI) in reducing positive margins after BCS. We sought to determine whether preoperative MRI was associated with reduced positive margins. PATIENTS AND METHODS: The SHAVE/SHAVE2 trials were multicenter trials in ten US centers with patients with stage 0-3 breast cancer undergoing BCS. Use of preoperative MRI was at the discretion of the surgeon. We evaluated whether or not preoperative MRI was associated with margin status prior to randomization regarding resection of cavity with shave margins. RESULTS: A total of 631 patients participated. Median age was 64 (range 29-94) years, with a median tumor size of 1.3 cm (range 0.1-9.3 cm). Patient factors included 26.1% of patients (165) had palpable tumors, and 6.5% (41) received neoadjuvant chemotherapy. Tumor factors were notable for invasive lobular histology in 7.0% (44) and extensive intraductal component (EIC) in 32.8% (207). A preoperative MRI was performed in 193 (30.6%) patients. Those who underwent preoperative MRI were less likely to have a positive margin (31.1% versus 38.8%), although this difference was not statistically significant (p = 0.073). On multivariate analysis, controlling for patient and tumor factors, utilization of preoperative MRI was not a significant factor in predicting margin status (p = 0.110). Rather, age (p = 0.032) and tumor size (p = 0.040) were the only factors associated with margin status. CONCLUSION: These data suggest that preoperative MRI is not associated margin status; rather, patient age and tumor size are the associated factors.

Changes in Surgical Management of the Axilla Over 11 Years - Report on More Than 1500 Breast Cancer Patients Treated with Neoadjuvant Chemotherapy on the Prospective I-SPY2 Trial.

BACKGROUND: Axillary surgery after neoadjuvant chemotherapy (NAC) is becoming less extensive. We evaluated the evolution of axillary surgery after NAC on the multi-institutional I-SPY2 prospective trial. METHODS: We examined annual rates of sentinel lymph node (SLN) surgery with resection of clipped node, if present), axillary lymph node dissection (ALND), and SLN and ALND in patients enrolled in I-SPY2 from January 1, 2011 to December 31, 2021 by clinical N status at diagnosis and pathologic N status at surgery. Cochran-Armitage trend tests were calculated to evaluate patterns over time. RESULTS: Of 1578 patients, 973 patients (61.7%) had SLN-only, 136 (8.6%) had SLN and ALND, and 469 (29.7%) had ALND-only. In the cN0 group, ALND-only decreased from 20% in 2011 to 6.25% in 2021 (p = 0.0078) and SLN-only increased from 70.0% to 87.5% (p = 0.0020). This was even more striking in patients with clinically node-positive (cN+) disease at diagnosis, where ALND-only decreased from 70.7% to 29.4% (p < 0.0001) and SLN-only significantly increased from 14.6% to 56.5% (p < 0.0001). This change was significant across subtypes (HR-/HER2-, HR+/HER2-, and HER2+). Among pathologically node-positive (pN+) patients after NAC (n = 525) ALND-only decreased from 69.0% to 39.2% (p < 0.0001) and SLN-only increased from 6.9% to 39.2% (p < 0.0001). CONCLUSIONS: Use of ALND after NAC has significantly decreased over the past decade. This is most pronounced in cN+ disease at diagnosis with an increase in the use of SLN surgery after NAC. Additionally, in pN+ disease after NAC, there has been a decrease in use of completion ALND, a practice pattern change that precedes results from clinical trials.

Omission of Radiation in Conservative Treatment for Breast Cancer: Opportunity for De-escalation of Care.

INTRODUCTION: De-escalation of breast cancer treatment aims to reduce patient and financial toxicity without compromising outcomes. Level I evidence and National Comprehensive Cancer Network guidelines support omission of adjuvant radiation in patients aged >70 y with hormone-sensitive, pT1N0M0 invasive breast cancer treated with endocrine therapy. We evaluated radiation use in patients eligible for guideline concordant omission of radiation. METHODS: Subgroup analysis of patients eligible for radiation omission from two pooled randomized controlled trials, which included stage 0-III breast cancer patients undergoing breast conserving surgery, was performed to evaluate factors associated with radiation use. RESULTS: Of 631 patients, 47 (7.4%) met radiation omission criteria and were treated by 14 surgeons at eight institutions. The mean age was 75.3 (standard deviation + 4.4) y. Majority of patients identified as White (n = 46; 97.9%) and non-Hispanic (n = 44; 93.6%). The mean tumor size was 1.0 cm; 37 patients (88.1%) had ductal, 4 patients (9.5%) had lobular, and 17 patients (40.5%) had low-grade disease. Among patients eligible for radiation omission, 34 (72.3%) patients received adjuvant radiation. Those who received radiation were significantly younger than those who did not (74 y, interquartile range = 4 y, versus 78 y, interquartile range = 11 y, P = 0.03). There was no difference in radiation use based on size (P = 0.4), histology (P = 0.5), grade (P = 0.7), race (P = 1), ethnicity (P = 0.6), institution (P = 0.1), gender of the surgeon (P = 0.7), or surgeon (P = 0.1). CONCLUSIONS: Fewer than 10% of patients undergoing breast conservation met criteria for radiation omission. Nearly three-quarters received radiation therapy with younger age being a driver of radiation use, suggesting ample opportunity for de-escalation, particularly among younger eligible patients.

Resection of Cavity Shave Margins in Stage 0-III Breast Cancer Patients Undergoing Breast Conserving Surgery: A Prospective Multicenter Randomized Controlled Trial.

OBJECTIVE: Single-center studies have demonstrated that resection of cavity shave margins (CSM) halves the rate of positive margins and re-excision in breast cancer patients undergoing partial mastectomy (PM). We sought to determine if these findings were externally generalizable across practice settings. METHODS: In this multicenter randomized controlled trial occurring in 9 centers across the United States, stage 0-III breast cancer patients undergoing PM were randomly assigned to either have resection of CSM ("shave" group) or not ("no shave" group). Randomization occurred intraoperatively, after the surgeon had completed their standard PM. Primary outcome measures were positive margin and re-excision rates. RESULTS: Between July 28, 2016 and April 13, 2018, 400 patients were enrolled in this trial. Four patients (2 in each arm) did not meet inclusion criteria after randomization, leaving 396 patients for analysis: 196 in the "shave" group and 200 to the "no shave" group. Median patient age was 65 years (range; 29-94). Groups were well matched at baseline for demographic and clinicopathologic factors. Prior to randomization, positive margin rates were similar in the "shave" and "no shave" groups (76/196 (38.8%) vs. 72/200 (36.0%), respectively, P = 0.604). After randomization, those in the "shave" group were significantly less likely than those in the "no shave" group to have positive margins (19/196 (9.7%) vs. 72/200 (36.0%), P < 0.001), and to require re-excision or mastectomy for margin clearance (17/196 (8.7%) vs. 47/200 (23.5%), P < 0.001). CONCLUSION: Resection of CSM significantly reduces positive margin and re-excision rates in patients undergoing PM.

Equine nonneoplastic abnormal ovary in a draft mare with high serum anti-Müllerian hormone: a case study.

We performed a standing hand-assisted laparoscopic ovariectomy in a draft mare that presented with high serum anti-Müllerian hormone (AMH) level and had an enlarged single cystic ovary. Histopathological examination revealed no tumor cell proliferation in the ovary, but the presence of a large ovarian cyst was confirmed. In the diagnosis of abnormal ovaries in mares, a comprehensive assessment should be performed, including the monitoring of ovarian morphology and biomarkers over time, to determine the disease prognosis and treatment plan. The case of this mare with a nonneoplastic abnormal ovary and increased serum AMH level was rare. We suggest that standing hand-assisted laparoscopic ovariectomy is useful for the removal of large ovaries in draft mares.

Ductal Carcinoma In Situ in Pregnant Women.

Breast cancer is the second most common malignancy affecting pregnant women. Ductal carcinoma in situ (DCIS) during pregnancy has not been well described with limited literature addressing the optimal treatment options. This is important topic as the incidence of pregnancy-associated breast cancer (PABC) has been increasing. In the United States, 1 in 3000 pregnancies are complicated by breast cancer diagnosis. Most DCIS are screen detected as most patients are asymptomatic. Since routine screening mammogram is not recommended during pregnancy, diagnosis of DCIS without invasive disease is uncommon diagnosis. Although PABC is reported to account for 0.2-3.8% of all newly diagnosed breast cancer, it has not been defined between the diagnosis of DCIS or invasive breast cancer making true incidence of DCIS in pregnancy difficult to report. This review summarizes multidisciplinary recommendations for optimal treatment for DCIS diagnosed during pregnancy.

Colostral and foal serum immunoglobulin G levels and associations with perinatal abnormalities in heavy draft horses in Japan.

The purpose of this study was to elucidate the colostral and foal serum immunoglobulin G (IgG) concentration values in heavy draft horses in Japan and to examine the effects of peripartum mare condition on colostral immunity. Colostrum was obtained 1 hr after foaling (pre-suckling; n=178). Blood was collected from the jugular vein of the foals (n=147) at 24 to 48 hr after birth. The foaling statuses of 73 mares were recorded. The average colostral IgG concentration was 10,540 ± 3,190 mg/dl (median=10,928; range 1,434-17,514 mg/dl). The average serum IgG concentration obtained from neonatal foals 24 to 48 hr after birth was 1,750 ± 919 mg/dl (median=1,890; range 0-3,510 mg/dl). Although colostral IgG did not differ between the normal foaling mare (n=59) and dystocial mare (n=14), foal serum IgG was lower in foals born in dystocia than in foals in normal foaling (P<0.05). This study demonstrates reference values for colostral and foal serum IgG specific to heavy draft horses in Japan and suggests that dystocia may interfere with the acquisition of colostral immunity in neonatal foals.

Relationship between the presence of intrauterine fluid and cervical bacteria in heavy draft mares before and after mating.

While intrauterine fluid (IUF) is observed as mucous in healthy mares during estrus, the presence of IUF during diestrus is an indicator of endometritis. Mating induces endometrial inflammation in healthy mares, called mating-induced endometritis, that disappears within 1-2 days after mating. On the other hand, it is also known that IUF remaining beyond 12 hr after mating can cause persistent inflammation, bacterial growth, and decreased fertility. This study aimed to investigate the relationship between the presence of IUF and cervical bacteria before and after mating. Mares were classified into three groups based on the degree of IUF: Grade 1 (G1), neither IUF nor echogenic lines at the inner lining of the uterus; Grade 2 (G2), small amount of IUF (<0.5 cm in diameter) or an echogenic lines in the intrauterine cavity; and Grade 3 (G3), obvious IUF (≥0.5 cm in diameter). The positive culture rates of G1, G2, and G3 mares before mating were 15.8% (n=6/38), 25.9% (n=7/27), and 31.8% (n=14/44), respectively, and did not differ significantly between the groups. After mating, the positive culture rates of G1, G2, and G3 mares were 18.2% (n=2/11), 56.1% (n=23/41), and 72.3% (n=34/47), respectively. The positive culture rates were significantly higher in G2 (P<0.05) and G3 (P<0.01) mares compared with G1 mares. These results from after mating suggest that not only mares with obvious IUF but also those with a small amount of IUF (<0.5 cm in diameter) or echogenic lines in the intrauterine cavity are at risk of mating-induced endometritis.