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PURPOSE Given the heterogeneity and improvement in outcomes for metastatic breast cancer (MBC), we developed a staging system that refines prognostic estimates for patients with metastatic cancer at the time of initial diagnosis, de novo MBC (dnMBC), on the basis of survival outcomes and disease-related variables. METHODS Patients with dnMBC (2010-2016) were selected from the National Cancer Database (NCDB). Recursive partitioning analysis (RPA) was used to group patients with similar overall survival (OS) on the basis of clinical T category, grade, estrogen receptor (ER), progesterone receptor, human epidermal growth factor receptor 2, histology, organ system site of metastases (bone-only, brain-only, visceral), and number of organ systems involved. Three-year OS rates were used to assign a final stage: IVA: >70%, IVB: 50%-70%, IVC: 25 to RESULTS At a median follow-up of 52.9 months, the median OS of the original cohort (N = 42,467) was 35.4 months (95% CI, 34.8 to 35.9). RPA stratified patients into 53 groups with 3-year OS rates ranging from 73.5% to 5.7%; these groups were amalgamated into four stage groups: 3-year OS, A = 73.2%, B = 61.9%, C = 40.1%, and D = 17% (log-rank P < .001). After bootstrapping, the survival outcomes for the four stages remained significantly different (log-rank P < .001). This staging system was then validated using SEER data (N = 20,469) and a separate cohort from the NCDB (N = 7,645) (both log-rank P < .001). CONCLUSION Our findings regarding the heterogeneity in outcomes for patients with dnMBC could guide future revisions of the current American Joint Committee on Cancer staging guidelines for patients with newly diagnosed stage IV disease. Our findings should be independently confirmed.

PURPOSE To determine if physicians' self-reported knowledge, attitudes, and practices regarding genetic counseling and testing (GCT) vary by patients' race. METHODS We conducted a nationwide 49-item survey among breast oncology physicians in the United States. We queried respondents about their own demographics, clinical characteristics, knowledge, attitudes, practices, and perceived barriers in providing GCT to patients with breast cancer. RESULTS Our survey included responses from 277 physicians (females, 58.8%; medical oncologists, 75.1%; academic physicians, 61.7%; and Whites, 67.1%). Only 1.8% indicated that they were more likely to refer a White patient than refer an African American patient for GCT, and 66.9% believed that African American women with breast cancer have lower rates of GCT than White women. Regarding perceived barriers to GCT, 63.4% of respondents indicated that African American women face more barriers than White women do and 21% felt that African American women require more information and guidance during the GCT decision-making process than White women. Although 32% of respondents indicated that lack of trust was a barrier to GCT in all patients, 58.1% felt that this was a greater barrier for African American women ( P < .0001). Only 13.9% believed that noncompliance with GCT is a barrier for all patients, whereas 30.6% believed that African American women are more likely than White women to be noncompliant ( P < .0001). CONCLUSION We demonstrated that racial differences exist in oncology physicians' perceived barriers to GCT for patients with breast cancer. This nationwide survey will serve as a basis for understanding physicians' determinants of GCT for African American women and highlights the necessity of education and interventions to address bias among physicians. Awareness of such physician biases can enable further work to address inequities, ultimately leading to improved GCT equity for African American women with breast cancer.

1095 Background: Treatments for metastatic breast cancer (MBC) have significantly improved survival for patients who receive treatment, yet data describing the prognosis for untreated patients is lacking. Therefore, we sought to assess the survival outcomes of patients with de novo MBC who did not receive treatment. Methods: Adults with MBC at diagnosis (clinical M1 or pathologic M1) were selected from the NCDB (2010-2016) and stratified based on receipt of treatment (treated = received at least one treatment; untreated = received no treatments). Differences between patient groups were tested using Chi-square tests for categorical variables and t-tests for continuous variables. Overall survival (OS) was estimated using the Kaplan-Meier method for the overall cohort and stratified by select patient and/or disease characteristics, and groups were compared with log-rank tests. Cox Proportional Hazards models were used to identify factors associated with OS in the untreated MBC subgroup. Results: Of the 53,240 patients with de novo MBC, the median age was 61y (IQR 52-71), and the majority had a comorbidity score of 0 (81.2%). Within this cohort, 49,040 (92.1%) received at least one treatment (treated) and 4,200 (7.9%) had no documented treatments (untreated). Untreated patients were more likely to be older (median 68y vs 61y, p < 0.001) and have higher comorbidity scores (p < 0.001). Patients with untreated MBC were more likely to have triple negative disease (17.8% vs 12.6%), and a higher disease burden (≥2 metastatic sites: 38.2% untreated vs 29.2% treated, p < 0.001). The median unadjusted OS in the untreated subgroup was 2.5mo vs 36.4mo in the treated subgroup (p < 0.001). For those who survived at least 1mo post-diagnosis, the median unadjusted OS in the untreated subgroup was 6.9mo vs 37.3mo in the treated subgroup (p < 0.001), which increased to 18.6mo and 40.3mo for those who survived at least 3mo post-diagnosis (p < 0.001). In the untreated population, unadjusted OS varied by breast cancer subtype (median 3.8mo for HR+/HER2-, vs 2.6mo for HER2+, vs 2.1mo for triple negative, p < 0.001) and number of metastatic sites (4.1mo for 1 site, vs 1.8mo for 2 sites, vs 1.1mo for 3 sites, vs 1.2mo for ≥4 sites, p < 0.001). After adjustment, variables associated with a worse OS in the untreated cohort included older age, higher comorbidity scores, higher tumor grade, and triple negative (vs HR+/HER2-) tumor subtype (all p < 0.05), while the number of metastatic sites was not associated with survival; these same findings were also noted when the analysis was limited to those who survived at least 1mo post-diagnosis. Conclusions: Patients with de novo MBC who do not receive treatment are more likely to be older, present with comorbid conditions, and have clinically aggressive disease. Similar to those who do receive treatment, survival in an untreated population is associated with select patient and disease characteristics. However, the prognosis for untreated MBC is dismal.

101 Background: Overall breast cancer mortality in the US has declined since 1990, but racial/ethnic disparities have worsened. Since 1992, NC BCCCP has provided free/low-cost breast cancer screening to underserved women as part of a national effort by the Centers for Disease Control and Prevention (CDC) to mitigate these disparities. We sought to characterize and evaluate benchmarks for this previously unstudied, state-level cohort. Methods: We identified women ≥18y who underwent their first breast cancer screening via NC BCCCP from 2009-2018. Univariate analysis was used to compare differences in timeline of care and rates of breast pathology (i.e., cancer or atypia) by race/ethnicity and age. Logistic and negative binomial regression were used to identify factors associated with cancer diagnosis and time from enrollment to diagnosis (TTD) and treatment (TTT), respectively. Results: 88,893 women with complete records were identified (median age 50y, IQR 44-56): 45.5% were Non-Hispanic (NH) white, 30.9% NH black, 19.5% Hispanic, 1.7% American Indian (AI), and 1.1% Asian. Overall participation peaked in 2012 but steadily increased among Hispanic women over time (p < 0.001). Breast pathology was diagnosed in 2,016 (2.3%) women, with rates ranging from 1% in Hispanic women to 2.7% in NH whites. After adjustment, Hispanic women were least likely (vs NH white women: OR 0.40; 95% CI 0.34-0.47) to be diagnosed with breast cancer. Median TTD was 19d and TTT was 33d, both within the CDC’s 60d standard. In univariate analyses, women < 50 had shorter TTD (median 18d vs 21d) and TTT (median 30d vs 35d) vs women ≥50 (both p < 0.01), and there were no significant differences by race/ethnicity or between women with atypia vs cancer. In multivariate models, however, older age and NH black race were associated with longer TTD and TTT. Conclusions: NC BCCCP meets national quality benchmarks for TTD and TTT. These data also highlight broader opportunities to achieve racial/ethnic parity and improve equity for breast cancer prevention. [Table: see text]

203 Background: Previous studies have demonstrated an association between body mass index (BMI) and survival after breast cancer diagnosis, but the direction and strength of this relationship is inconsistent. Comorbidities that are more common in patients who are obese (BMI≥30) – including diabetes (DM), hypertension (HTN), and hyperlipidemia (HLD) – are often conflated with obesity with regard to their effects on breast cancer outcomes. We sought to determine the effect of BMI on overall survival (OS) among women with breast cancer after controlling for obesity-associated conditions. Methods: Women≥18y diagnosed with stage 0-IV breast cancer at an academic institution from Jan 2014-Jul 2016 and with known BMI at diagnosis were identified. χ2 and ANOVA tests were used to compare intergroup differences. BMI was categorized as normal (

e19114 Background: National cancer registries are valuable tools used to analyze patterns of care and clinical oncology outcomes; yet, patients with missing data may impact the accuracy and generalizability of these data. We sought to evaluate the association between missing data and overall survival (OS). Methods: Using the NCDB and SEER, we compared data missingness among patients diagnosed with invasive breast cancer from 2010-2014. Key variables included: demographic variables (age, race, ethnicity, insurance, education, income), tumor variables (grade, ER, PR, HER2, TNM stage), and treatment variables (surgery in both databases; chemotherapy and radiation in NCDB). OS was compared between those with and without missing data via Cox proportional hazards models. Results: Overall, 775,996 patients in the NCDB and 263,016 in SEER were identified; missingness of at least 1 key variable was 29% and 13%, respectively. Of those, the majority were missing a tumor variable (NCDB 80%; SEER 88%), while demographic and treatment variables were missing less often. When compared to patients with complete data, missingness was associated with a greater risk of death; NCDB 17% vs. 14% (HR 1.23, 99% CI 1.21-1.25) and SEER 27% vs 14% (HR 2.11, 99% CI 2.05-2.18). Rate of death was similar whether the patient was missing 1 or ≥2 variables. When stratified by the type of missing variable, differences in OS between those with and without missing data in the NCDB were small. In SEER, reductions in OS were largest for those missing tumor variables (HR 2.26, 99% CI 2.19-2.33) or surgery data (HR 3.84, 99% CI 3.32-4.45). Among the tumor variables specifically, few clinically meaningful differences in OS were noted in the NCDB, while the most significant differences in SEER were noted in T and N stage (table). Conclusions: Missingness of select variables is associated with a worse OS and is not uncommon within large national cancer registries. Therefore, researchers must use caution when choosing inclusion/exclusion criteria for outcomes studies. Future research is needed to elucidate which patients are most often missing data and why OS differences are observed. [Table: see text]

1516 Background: The proportion of germline versus somatic mutations identified on genomic tumor testing of solid malignancies is not well characterized. We compared somatic and germline testing results in patients with breast, ovarian, pancreatic or prostate cancer with a genomic alteration identified on tumor testing. Methods: Retrospective chart review was performed using a tertiary care academic center’s database of somatic tumor testing results obtained via FoundationOne and Guardant testing. Patients with breast, ovarian, pancreatic or prostate cancer who had a genomic alteration identified on tumor testing, including pathogenic and VUS variants, in BRCA1or BRCA2, CHEK2, ATM, BRIP1, RAD51C, RAD51D, PALB2and CDH1and who had also received germline testing were identified. Analysis was performed to assess prevalence of germline results. The association between mutant allele fraction (MAF) and germline mutation status was also assessed. Results: Results: 124 patients with breast, ovarian, pancreatic or prostate cancer were identified who had a genomic alteration of interest also tested for via germline testing. 54 (32.5%) of tumor mutations were also identified on germline testing. Proportion of genomic results that were germline was wide, ranging from 0-85.7% depending on the gene and variant classification (Table). Germline mutations were present in 36.4% of breast, 25% of ovarian, 53.3% of pancreatic, and 20.9% of prostate cancer patients who had a tumor alteration present. Alterations that were found to be concordant in both somatic and germline testing had an average MAF of 0.54, and alterations identified on somatic testing only had an average MAF of 0.30. Conclusions: Our findings suggest that approximately one-third of genomic alterations on tumor testing will be of germline origin. However, concordance rates may be gene and variant dependent. Higher MAF may be associated with germline alteration status, but further evaluation is needed. Thus, while information provided by genomic tumor testing may be suggestive of a correlating germline mutation, no single alteration type or MAF value is reliably predictive. [Table: see text]

e13083Background: Although current staging guidelines for early stage breast cancer now include anatomic and biologic factors, there are no standard prognostic models for estimating outcomes in met...

585Background: Increased tumor infiltrating lymphocytes (TILs) are predictive and prognostic for improved outcomes in breast cancers. Increased tumor mutational burden can be immune activating. BRC...

587Background: Breast cancer patients with invasive lobular carcinoma (ILC) have lower rates of downstaging after neoadjuvant chemotherapy (NACT) than those with invasive ductal carcinoma; however,...

532 Background: Metaplastic breast cancer (MBC) is a rare, aggressive variant that is often triple negative (TN). Current guidelines recommend use of standard receptor-based treatment for MBC despite evidence of chemoresistance. We sought to compare treatment patterns and outcomes of MBC and non-MBC. Methods: Women age > 18 with stage I-III MBC and non-MBC histology diagnosed from 2010-2013 were identified in the National Cancer Database. Kaplan Meier and multivariate Cox proportional hazards models were used to estimate MBC association with overall survival (OS). Subgroup analyses were conducted for (1) MBC patients only and (2) TN MBC and TN non-MBC patients. Results: 2451 MBC and 568,057 non-MBC patients were included. 70.3% of MBC were TN vs 11.3% of non-MBC (p < 0.001). 19.2% of MBC were luminal (i.e., ER+ and/or PR+, and HER2-). MBC presented with higher clinical T stage (cT4: 5.4% vs 1.8%) and grade (grade 3: 72.1% vs 29.7%) but was less frequently node-positive (19.1% vs 29.7%, all p < 0.001). A higher proportion of MBC patients were treated with mastectomy (59.0% vs 44.9%), axillary dissection (ALND, 35.2% vs 32.2%), and chemotherapy (74.1% vs 43.1%, all p≤0.001). 5-year OS was reduced among MBC vs non-MBC patients for both the entire cohort (72.7% vs 87.5%) and the TN-only analysis (71.1% vs 77.8%, both log-rank p < 0.001). Among MBC cases, TN subtype was not associated with worse OS than the luminal subtype (HR 1.16, p = 0.28). Chemotherapy (HR 0.69, p = 0.004) and/or radiotherapy (HR 0.52, p < 0.001) improved OS in MBC, and the proportional benefit of chemotherapy did not vary with pathological T or N stage (interaction p > 0.05 for both). Among TN patients, a higher proportion of TN MBC patients underwent mastectomy (58.4% vs 49.5%, p < 0.001), but in contrast to the full cohort, a lower proportion of TN MBC patients received chemotherapy (76.6% vs. 78.7%, p = 0.008) and ALND (35.2% vs. 38.2%, p = 0.01) vs TN non-MBC patients. Conclusions: MBC had worse OS vs non-MBC, and unlike other histologies, outcome was not driven by receptor status. Multimodal therapy improved outcomes. Further investigation into MBC tumor biology and the development of MBC-specific guidelines could potentially improve treatment standardization and outcomes.

e18144 Background: Breast oncologists have little guidance on predicting long term outcomes after interval survival. We aim to evaluate the association of overall survival (OS) with select factors at multiple time points. Methods: Women ages 18-80 with non-metastatic invasive breast cancer were identified from the NCDB (2004─2014). Using multivariate survival analysis, we estimated the association of OS with tumor and treatment factors for those with follow up surviving at least 2, 5, and 10y post-diagnosis. Results: 685598 women (median age 59) were identified; 573757 were alive with follow up at 2y, 254303 at 5y, and 18640 at 10y. The majority had early stage, hormone receptor (HR) +, invasive ductal carcinoma. 57% underwent lumpectomy; 49% received chemotherapy; 89% of lumpectomies received radiation (RT); and 83% of HR+ tumors received endocrine therapy (ET). Of those alive at 2y, improved OS was associated with ER+, PR+, chemotherapy, RT, and ET. Reduced OS was associated with higher cT/cN stage, grade, and mastectomy. Of those alive at 5y, improved OS was associated with chemotherapy, RT, and ET. Reduced OS was associated with higher cT/cN stage, grade, and mastectomy. Of those alive at 10y, reduced OS was associated with higher cT stage and grade. Conclusions: Tumor and treatment factors are associated with OS, but the association of some factors may change for women surviving at least 5y or 10y. These findings may contribute to more tailored prognostication for patients based on interval survival. [Table: see text]

1570 Background: Metaplastic breast cancer (MBC) is a rare, aggressive, sarcomatoid breast cancer that was first described in 1973 but only became recognized as a histologically distinct entity in 2000. Given the paucity of data on the epidemiology of MBC, we performed a population-based analysis to delineate sociodemographic and clinicopathological characteristics associated with increased likelihood of MBC diagnosis. Methods: Adult female breast cancer patients with stage I-III MBC and non-MBC histology diagnosed between 2010 and 2013 were identified in the National Cancer Database (NCDB). Multivariate logistic regression was used to identify factors associated with diagnosis of MBC, and Cox proportional hazards modeling was used to estimate the effect of MBC on overall survival. Results: 2,451 MBC and 568,057 non-MBC patients were identified. After adjusting for receptor status (ER, PR, HER2), age, stage, grade, and treatment variables, MBC patients had worse survival than non-MBC patients (HR 1.45, p < 0.001). Compared to non-MBC patients, a higher proportion of MBC patients were non-Hispanic black (16.7% vs 10.5%), had an annual income < $35k (29.0% vs 25.5%), had lower high school completion rates (36.7% vs 33.9%), were treated at academic centers (35.5% vs 30.8%), and had government-sponsored insurance (48.8% vs 43.7%, all p < 0.01). MBC diagnosis was more likely in patients with triple-negative breast cancer (OR 20.71), higher clinical T stage (cT4 vs cT1: OR 6.18), and lower clinical N stage (cN1 vs cN0: OR 0.38, all p < 0.001). MBC patients were also more likely to be diagnosed based on pathology from their first operation rather than preoperatively (OR 1.41, p < 0.001). Conclusions: Black women and women of low socioeconomic status were at increased risk for diagnosis with MBC. Though MBC was more likely to be treated at academic centers, MBC was less likely to be diagnosed prior to surgical intervention. Many of the sociodemographic factors associated with MBC have also been associated with triple-negative breast cancer. Additional research is needed to determine the contribution of sociodemographic factors to the epidemiology of MBC independent of receptor status.

1557Background: The new ACS screening mammography guidelines suggest that only women with an above average risk require mammography screening between ages 40-44 (≥15% lifetime risk of breast cancer...

60 Background: Standard follow-up imaging for women with a history of breast cancer is well defined, but the appropriate screening guidelines for other high risk breast lesions, such as atypical ductal hyperplasia (ADH), remain unclear. Current practices often parallel those of cancer patients and include a 6 month interval mammogram prior to resuming annual screening, which may be unnecessary. As such, it is critical to evaluate the utility of the current standard practice of additional screening beyond a routine annual mammogram. Methods: Our pathology database was queried for the phrase "atypical ductal hyperplasia" from 2008 to 2010, and patients who underwent surgical excision were identified. Those who did not have subsequent follow up at our institution were excluded. Results: There were 44 patients who underwent excisional biopsies that were diagnosed with ADH and proceeded with follow up. In addition to a routine clinical exam, a short-term follow up diagnostic mammogram was performed in 24 patients. The median age was 56.5 years, and the median breast cancer risk assessment scores were 2.8% at 5 years and 13.4% lifetime. Of the 24 interval mammograms, 21 yielded benign findings on initial imaging (BIRADS 2), while 3 patients (12.5%) required additional imaging that ultimately resulted in benign findings. There were only 4 patients with a lifetime risk ≥25%, and all of these patients had benign findings on their initial imaging and resumed routine follow up. To date, 22 patients have received at least one additional mammogram, and all subsequent findings have been benign. No additional biopsies or surgeries have been performed. Conclusions: In sum, a clinical exam is still recommended at 6 months following surgical excision for a diagnosis of ADH. In the post-surgical breast, imaging may be misleading and result in psychological distress for patients and possibly unnecessary procedures. Based on our findings, a 6-month follow up mammogram is not recommended and patients should resume annual surveillance.