Patient-derived response estimates from zero-passage organoids of luminal breast cancer.

Background: Primary luminal breast cancer cells lose their identity rapidly in standard tissue culture, which is problematic for testing hormone interventions and molecular pathways specific to the luminal subtype. Breast cancer organoids are thought to retain tumor characteristics better, but long-term viability of luminal-subtype cases is a persistent challenge. Our goal was to adapt short-term organoids of luminal breast cancer for parallel testing of genetic and pharmacologic perturbations. Methods: We freshly isolated patient-derived cells from luminal tumor scrapes, miniaturized the organoid format into 5 µl replicates for increased throughput, and set an endpoint of 14 days to minimize drift. Therapeutic hormone targeting was mimicked in these "zero-passage" organoids by withdrawing ß-estradiol and adding 4-hydroxytamoxifen. We also examined sulforaphane as an electrophilic stress and commercial neutraceutical with reported anti-cancer properties. Downstream mechanisms were tested genetically by lentiviral transduction of two complementary sgRNAs and Cas9 stabilization for the first week of organoid culture. Transcriptional changes were measured by RT-qPCR or RNA sequencing, and organoid phenotypes were quantified by serial brightfield imaging, digital image segmentation, and regression modeling of cellular doubling times. Results: We achieved >50% success in initiating luminal breast cancer organoids from tumor scrapes and maintaining them to the 14-day zero-passage endpoint. Success was mostly independent of clinical parameters, supporting general applicability of the approach. Abundance of ESR1 and PGR in zero-passage organoids consistently remained within the range of patient variability at the endpoint. However, responsiveness to hormone withdrawal and blockade was highly variable among luminal breast cancer cases tested. Combining sulforaphane with knockout of NQO1 (a phase II antioxidant response gene and downstream effector of sulforaphane) also yielded a breadth of organoid growth phenotypes, including growth inhibition with sulforaphane, growth promotion with NQO1 knockout, and growth antagonism when combined. Conclusions: Zero-passage organoids are a rapid and scalable way to interrogate properties of luminal breast cancer cells from patient-derived material. This includes testing drug mechanisms of action in different clinical cohorts. A future goal is to relate inter-patient variability of zero-passage organoids to long-term outcomes.

Are There Disparities in Breast Reconstruction After Contralateral Prophylactic Mastectomy?

INTRODUCTION: Despite national guidelines against contralateral prophylactic mastectomy (CPM) in low- to moderate-risk breast cancer, CPM use continues to rise. Breast reconstruction improves health-related quality of life and satisfaction among women undergoing mastectomy. Given the lack of data regarding factors associated with reconstruction after CPM and the known benefits of reconstruction, we sought to investigate whether disparities exist in receipt of reconstruction after CPM. METHODS: The 2004-2017 National Cancer Database was queried to identify women diagnosed with breast cancer who underwent unilateral mastectomy with CPM. Patients were divided into two groups: those who underwent planned reconstruction at any timepoint and those who did not. A secondary analysis comparing types of reconstruction (tissue, implant, combined) was conducted. Patient, tumor, and demographic characteristics were analyzed using chi-square test and odds ratios were calculated using generalized estimating equations. RESULTS: The cohort included 1,73,249 women: 95,818 (55.3%) underwent reconstruction and 77,431 (45.7%) did not. Both the rate CPM and the proportion of women undergoing reconstruction after CPM increased between 2004 and 2017. Of the women who had reconstruction, 40,840 (51.7%) received implants, 29,807 (37.7%) had tissue, and 8352 (10.6%) had combined reconstruction. After adjusted analysis, factors associated with reconstruction were young age, Hispanic ethnicity, private insurance, and living in an area with the highest education and median income (P < 0.01). Patients who underwent reconstruction were less likely to have radiation (P < 0.01) and chemotherapy (P < 0.01), more likely to have stage I disease (P < 0.01), and to be treated at an integrated cancer center (P < 0.01). CONCLUSIONS: Reconstruction after CPM is disproportionately received by younger women, Hispanics, those with private insurance, and higher socioeconomic status and education. While the rate of reconstruction after CPM is increasing, there remain significant disparities. Conscious efforts must be made to eliminate these disparities, especially given the known benefits of reconstruction after mastectomy.

Society of Surgical Oncology Breast Disease Site Working Group Statement on Contralateral Mastectomy: Indications, Outcomes, and Risks.

Rates of contralateral mastectomy (CM) among patients with unilateral breast cancer have been increasing in the United States. In this Society of Surgical Oncology position statement, we review the literature addressing the indications, risks, and benefits of CM since the society's 2017 statement. We held a virtual meeting to outline key topics and then conducted a literature search using PubMed to identify relevant articles. We reviewed the articles and made recommendations based on group consensus. Patients consider CM for many reasons, including concerns regarding the risk of contralateral breast cancer (CBC), desire for improved cosmesis and symmetry, and preferences to avoid ongoing screening, whereas surgeons primarily consider CBC risk when making a recommendation for CM. For patients with a high risk of CBC, CM reduces the risk of new breast cancer, however it is not known to convey an overall survival benefit. Studies evaluating patient satisfaction with CM and reconstruction have yielded mixed results. Imaging with mammography within 12 months before CM is recommended, but routine preoperative breast magnetic resonance imaging is not; there is also no evidence to support routine postmastectomy imaging surveillance. Because the likelihood of identifying an occult malignancy during CM is low, routine sentinel lymph node surgery is not recommended. Data on the rates of postoperative complications are conflicting, and such complications may not be directly related to CM. Adjuvant therapy delays due to complications have not been reported. Surgeons can reduce CM rates by encouraging shared decision making and informed discussions incorporating patient preferences.

Novel Form of Breast Intraoperative Radiation Therapy with CT-Guided High-Dose-Rate Brachytherapy: Interim Results of a Prospective Phase-II Clinical Trial.

BACKGROUND: Precision breast intraoperative radiation therapy (PB-IORT) is a novel method of IORT that uses customized CT-based treatment plans and high-dose-rate (HDR) brachytherapy. We conducted a phase-II multi-institution trial to evaluate the efficacy of PB-IORT. STUDY DESIGN: Between 2015 and 2022, 3 centers enrolled women aged 45 years and older with invasive or in situ carcinoma measuring 3 cm or smaller and N0 status (n = 358). Breast-conserving surgery was performed, and a multilumen balloon catheter was placed in the lumpectomy bed. CT images were used to create customized HDR brachytherapy plans that delivered 12.5 Gy to the tumor bed. The primary outcome assessed was the 5-year rate of index quadrant tumor recurrence. An interim analysis was conducted after one-third of eligible participants completed 5 years of follow-up. This trial is registered with clinicaltrials.gov (NCT02400658). RESULTS: The cohort comprised 153 participants with a median age of 64 years and median follow-up time of 5.9 years. The estimated 5-year index quadrant tumor recurrence rate and overall survival were 5.08% (95% CI 2.23 to 9.68) and 95.1%, respectively. Locoregional (ipsilateral breast and axilla) and distant recurrence rates were each 1.96%. Seven deaths occurred during the first 5 years of follow-up, with only 1 attributable to breast cancer. Overall, 68.6% of patients experienced any adverse effects, and 4 cases of breast-related severe toxicities were observed. CONCLUSIONS: This study presents the results of a planned interim analysis of a phase-II trial investigating PB-IORT and demonstrates the efficacy and safety of single-fraction, CT-based, HDR brachytherapy after breast-conserving surgery. These findings provide valuable insights into the use of PB-IORT as a treatment modality.

The POWER-PAK Score Characterizes Tumor Response to 3 Months of Preoperative Endocrine Therapy.

BACKGROUND: The Pre-Operative Window of Endocrine Therapy to Inform Radiation Therapy Decisions (POWER, NCT04272801) trial aims to determine whether 3 months of preoperative endocrine therapy (pre-ET) informs adjuvant radiation therapy decisions among older women with early stage, ER-positive breast cancer. We propose the POWER Pathologic Assessment and Ki-67 (POWER-PAK) scoring system to characterize the histologic effects of pre-ET. METHODS: Histologic evaluation was performed on core biopsy and lumpectomy specimens from 37 POWER trial participants who completed pre-ET and surgery. The POWER-PAK score consists of tumor regression, decrease in Ki-67 expression, and ER expression, each ranging from 0 to 2. Scores were aggregated to create the POWER-PAK score with a range from 0 to 6. Participants with no residual tumor were labelled 6-NRT. RESULTS: ER expression did not decrease after pre-ET. Ki-67 decreased from 13% in biopsy specimens to 5% in the lumpectomy specimens (p < 0.001). Cellularity decreased from 40% to 23% (p < 0.001). There was heterogeneity of POWER-PAK scores ranging from 2 to 6-NRT: score of 2, n = 2 (5.4%); 4, n = 8 (21.6%); 5, n = 4 (10.8%); 6, n = 16 (43.2%); and 6-NRT, n = 7 (18.9%). Participants with a score ≥ 5 were more likely to have smaller tumors after pre-ET compared with those with a score < 5 (p = 0.04). CONCLUSIONS: The tumor responses following treatment with pre-ET are heterogenous. We propose that the POWER-PAK scoring system can be used to quantify response to pre-ET. Future studies will explore the use of POWER-PAK to support informed decision-making for adjuvant therapy options for older women with early stage breast cancer.

Cancer Screening and Treatment Delays During the COVID-19 Pandemic and the Role of Health Literacy in Care Re-engagement: Findings from an NCI-Designated Comprehensive Cancer Center sample.

The COVID-19 pandemic has led to numerous delays in cancer-related care and cancer-specific screening, but the extent is not fully understood. For those that experience a delay or disruption in care, health related self-management is required to re-engage in care pathways and the role of health literacy in this pathway has not been explored. The purpose of this analysis is to (1) report the frequency of self-reported delays in cancer treatment and preventative screening services at an academic, NCI-designated center during the COVID-19 pandemic and (2) investigate cancer-related care and screening delays among those with adequate and limited health literacy. A cross-sectional survey was administered from an NCI-designated Cancer Center with a rural catchment area during November 2020 through March 2021. A total of 1,533 participants completed the survey, and nearly 19 percent of participants were categorized as having limited health literacy. Twenty percent of those with a cancer diagnosis reported a delay in cancer-related care; and 23-30% of the sample reported a delay in cancer screening. In general, the proportions of delays among those with adequate and limited health literacy were similar with the exception of colorectal cancer screening. There was also a notable difference in the ability to re-engage in cervical cancer screening among those with adequate and limited health literacy. Thus, there is a role for those engaged in cancer-related education and outreach to offer additional navigation resources for those at risk to cancer-related care and screening disruptions. Future study is warranted to investigate the role of health literacy on cancer care engagement.

Long-Term Adherence to Adjuvant Endocrine Therapy Following Various Radiotherapy Modalities in Early Stage Hormone Receptor Positive Breast Cancer.

INTRODUCTION: We compared the rates of long-term adjuvant endocrine therapy (AET) adherence after various radiation therapy (RT) modalities among patients with early stage breast cancer. MATERIALS AND METHODS: Medical records from patients with stage 0, I, or IIA (tumors ≤3 cm), hormone receptor (HR) positive breast cancer that received adjuvant radiation therapy (RT) from 2013 to 2015 at a single institution were retrospectively reviewed. All patients received breast conserving surgery (BCS) followed by adjuvant RT via one of the following modalities: whole breast radiotherapy (WBI), partial breast irradiation (PBI) with either external beam radiation therapy (EBRT) or fractionated intracavitary high-dose rate (HDR) brachytherapy, or single fraction HDR-brachytherapy intraoperative-radiation therapy (IORT). RESULTS: One hundred fourteen patients were reviewed. Thirty patients received WBI, 41 PBI, and 43 IORT with a median follow up of 64.2, 72.0, and 58.6 months, respectively. For the entire cohort, AET adherence was approximately 64% at 2 years and 56% at 5 years. Among patients in the IORT clinical trial, adherence to AET was approximately 51% at 2 years and 40% at 5 years. After controlling for additional factors, DCIS histology (vs invasive disease) and IORT (compared to other radiation modalities) were associated with decreased endocrine therapy adherence (P < 0.05). CONCLUSION: DCIS histology and receipt of IORT were associated with lower rates of adherence to AET at 5 years. Our findings suggest that examination of the efficacy of RT interventions such as PBI and IORT in patients who do not receive AET is warranted.

Factors Associated With Cosmetic Outcomes After Treatment With a Novel Form of Breast Intraoperative Radiation Therapy.

INTRODUCTION: Precision breast intraoperative radiation therapy (PB-IORT) incorporates computed tomography-guided treatment planning and high dose rate brachytherapy to deliver a single dose of highly conformal radiational therapy. The purpose of this study is to determine factors associated with poor cosmetic outcomes after treatment with PB-IORT. METHODS: The study included all consecutive participants enrolled in an ongoing phase II clinical trial that had completed a minimum of 12 mo of follow-up. A poor cosmetic outcome was defined as scoring "fair" or "poor" on the Harvard Cosmesis evaluation, or "some" or "very much" on any of the three general cosmesis categories. Statistical analysis was performed utilizing R. RESULTS: The final cohort included 201 participants, of which 181 (90%) had an overall good/excellent cosmetic outcome. Group 1 consisted of 162 (81%) participants who reported only excellent/good cosmetic outcomes. Group 2 consisted of 39 (19%) participants who reported some aspect of a poor cosmetic outcome. On multivariable analysis, participants with ductal carcinoma in situ were significantly more likely to experience a poor cosmetic outcome (odds ratio 2.45, 95% confidence interval 1.03-5.82, P = 0.04), and those who received subsequent whole breast irradiation were also more likely to have a poor cosmetic outcome (odds ratio 10.20, 95% confidence interval CI 1.04-99.95, P = 0.04). CONCLUSIONS: Patients with need for further radiation after PB-IORT are at increased risk for a poor cosmetic outcome. Larger balloon volume and distance between the skin do not have deleterious effects on cosmetic outcomes.

Clinical Trials in Breast Cancer: Practice Changing, Landmark with a Focus on More Current Trials.

Randomized clinical trials have been essential in guiding the surgical and systemic treatment of breast cancer, with most focusing on de-escalation. Here, we discuss key clinical trials that have shaped the modern approach to the treatment of breast cancer, focusing on studies that are more recent.

A comparative study using time-driven activity-based costing in single-fraction breast high-dose rate brachytherapy: An integrated brachytherapy suite vs. decentralized workflow.

INTRODUCTION: Precision breast intraoperative radiation therapy (PB-IORT) is a novel approach to adjuvant radiation therapy for early-stage breast cancer performed as part of a phase II clinical trial at two institutions. One institution performs the entire procedure in an integrated brachytherapy suite which contains a CT-on-rails imaging unit and full anesthesia capabilities. At the other, breast conserving surgery and radiation therapy take place in two separate locations. Here, we utilize time-driven activity-based costing (TDABC) to compare these two models for the delivery of PB-IORT. METHODS: Process maps were created to describe each step required to deliver PB-IORT at each institution, including personnel, equipment, and supplies. Time investment was estimated for each step. The capacity cost rate was determined for each resource, and total costs of care were then calculated by multiplying the capacity cost rates by the time estimate for the process step and adding any additional product costs. RESULTS: PB-IORT costs less to deliver at a distributed facility, as is more commonly available, than an integrated brachytherapy suite ($3,262.22 vs. $3,996.01). The largest source of costs in both settings ($2,400) was consumable supplies, including the brachytherapy balloon applicator. The difference in costs for the two facility types was driven by personnel costs ($1,263.41 vs. $764.89). In the integrated facility, increased time required by radiation oncology nursing and the anesthesia attending translated to the greatest increases in cost. Equipment costs were also slightly higher in the integrated suite setting ($332.60 vs. $97.33). CONCLUSIONS: The overall cost of care is higher when utilizing an integrated brachytherapy suite to deliver PB-IORT. This was primarily driven by additional personnel costs from nursing and anesthesia, although the greatest cost of delivery in both settings was the disposable brachytherapy applicator. These differences in cost must be balanced against the potential impact on patient experience with these approaches.

Effects of a novel form of intraoperative radiation therapy on quality of life among patients with early-stage breast cancer.

PURPOSE: To investigate patient-perceived quality of life (QOL) among patients treated with a novel form of breast intraoperative radiation therapy (PB-IORT). METHODS AND MATERIALS: Patients treated with PB-IORT as part of a phase II clinical trial from 2013 to 2020 were identified. Patients were given the European Organization for Research and Treatment of Cancer (EORTC) core 30-item Quality of Life Questionnaire (QLQ-C30) encompassing global health, functionality, and symptomatology at baseline, 1-month, 6-months, 12-months, and 24-months after PB-IORT. Scores were on a 100-point scale with change greater than 10 considered clinically significant. Scores at interval follow-up were compared to baseline using repeated measure modeling with an unstructured covariance matrix. RESULTS: The cohort consisted of 303 patients, a majority of which were White (84.2%) with a median age of 64 years (IQR: 52, 76). One month after PB-IORT, a decline from baseline in physical (-2.5, 95% CI: -4.4 - -0.55, p = 0.01), role (-7.6, 95% CI: -11.7 - -3.5, p < 0.001), and social functioning (-3.0, 95% CI: -5.5 - -0.42, p = 0.02) were observed, which correlated with increased fatigue (8.4, 95% CI: 5.5-11.3, p < 0.001). At 6 months, nearly all QOL measures returned to baseline or improved. There were no statistically or clinically significant differences from baseline in overall global health. All functional and symptom scale differences were less than 10, indicating minimal clinical significance. CONCLUSIONS: PB-IORT has minimal negative impact on QOL, further supporting this patient-centered treatment approach for early-stage breast cancer.

Disparities in telemedicine utilization among surgical patients during COVID-19.

BACKGROUND: Telemedicine has been rapidly adopted in the wake of the COVID-19 pandemic. There is limited work surrounding demographic and socioeconomic disparities that may exist in telemedicine utilization. This study aimed to examine demographic and socioeconomic differences in surgical patient telemedicine usage during the COVID-19 pandemic. METHODS: Department of Surgery outpatients seen from July 1, 2019 to May 31, 2020 were stratified into three visit groups: pre-COVID-19 in-person, COVID-19 in-person, or COVID-19 telemedicine. Generalized linear models were used to examine associations of sex, race/ethnicity, Distressed Communities Index (DCI) scores, MyChart activation, and insurance status with telemedicine usage during the COVID-19 pandemic. RESULTS: 14,792 patients (median age 60, female [57.0%], non-Hispanic White [76.4%]) contributed to 21,980 visits. Compared to visits before the pandemic, telemedicine visits during COVID-19 were more likely to be with patients from the least socioeconomically distressed communities (OR, 1.31; 95% CI, 1.08,1.58; P = 0.005), with an activated MyChart (OR, 1.38; 95% CI, 1.17-1.64; P < .001), and with non-government or commercial insurance (OR, 2.33; 95% CI, 1.84-2.94; P < .001). Adjusted comparison of telemedicine visits to in person visits during COVID-19 revealed telemedicine users were more likely to be female (OR, 1.38, 95% CI, 1.10-1.73; P = 0.005) and pay with non-government or commercial insurance (OR, 2.77; 95% CI, 1.85-4.16; P < .001). CONCLUSIONS: During the first three months of the COVID-19 pandemic, telemedicine was more likely utilized by female patients and those without government or commercial insurance compared to patients who used in-person visits. Interventions using telemedicine to improve health care access might consider such differences in utilization.

Impact of the COVID-19 pandemic on breast cancer screening volumes and patient screening behaviors.

PURPOSE: In order to facilitate targeted outreach, we sought to identify patient populations with a lower likelihood of returning for breast cancer screening after COVID-19-related imaging center closures. METHODS: Weekly total screening mammograms performed throughout 2019 (baseline year) and 2020 (COVID-19-impacted year) were compared. Demographic and clinical characteristics, including age, race, ethnicity, breast density, breast cancer history, insurance status, imaging facility type used, and need for interpreter, were compared between patients imaged from March 16 to October 31 in 2019 (baseline cohort) and 2020 (COVID-19-impacted cohort). Census data and an online map service were used to impute socioeconomic variables and calculate travel times for each patient. Logistic regression was used to identify patient characteristics associated with a lower likelihood of returning for screening after COVID-19-related closures. RESULTS: The year-over-year cumulative difference in screening mammogram volumes peaked in week 21, with 2962 fewer exams in the COVID-19-impacted year. By week 47, this deficit had reduced by 49.4% to 1498. A lower likelihood of returning for screening after COVID-19-related closures was independently associated with younger age (odds ratio (OR) 0.78, p < 0.001), residence in a higher poverty area (OR 0.991, p = 0.014), lack of health insurance (OR 0.65, p = 0.007), need for an interpreter (OR 0.68, p = 0.029), longer travel time (OR 0.998, p < 0.001), and utilization of mobile mammography services (OR 0.27, p < 0.001). CONCLUSION: Several patient factors are associated with a lower likelihood of returning for screening mammography after COVID-19-related closures. Knowledge of these factors can guide targeted outreach to vulnerable patients to facilitate breast cancer screening.

Effects of Adjuvant Endocrine Therapy Adherence and Radiation on Recurrence and Survival Among Older Women with Early-Stage Breast Cancer.

BACKGROUND: The Cancer and Leukemia Group-B 9343 (CALGB 9343) trial demonstrated that women aged ≥ 70 years with early-stage breast cancer can safely omit radiation therapy (RT) and be treated with breast-conserving surgery (BCS) and adjuvant endocrine therapy (AET) alone. AET adherence is low, leaving an undertreated cohort who may be at increased risk of recurrence and death. We hypothesized that AET adherence and adjuvant treatment choice impact recurrence and survival among CALGB 9343 eligible women. PATIENTS AND METHODS: SEER-Medicare was used to identify CALGB 9343 eligible women who underwent BCS between 2007 and 2016. Medicare claims were used to identify AET use, and the proportion of days covered by AET was used to categorize adherent (PDC ≥ 0.80) versus nonadherent patients (PDC < 0.80). Recurrence-free, cancer-specific, and overall survival were assessed using Cox proportional hazards models. RESULTS: In total, 10,719 women were identified, of whom 780 (7.3%) underwent BCS alone, 1490 (13.9%) underwent BCS + RT, 1663 (15.5%) underwent BCS + AET, and 6786 (63.3%) had BCS + RT + AET. Among women treated with BCS + AET, adherent patients had lower recurrence than did nonadherent patients (HR = 0.65, 95% CI: 0.50-0.85). With respect to adjuvant treatment combinations, there was no recurrence difference between the BCS + RT + AET group and BCS + AET group (HR = 0.81, 95% CI: 0.54-1.21). There was equivalent cancer-specific but worse overall survival in the BCS + AET group versus the BCS + AET + RT group. CONCLUSIONS: While BCS + RT + AET may represent overtreatment for some, AET nonadherent women who omit RT are at risk for worse outcomes. Treatment decisions regarding RT omission should be tailored to the individual patient, taking into consideration the chances of AET nonadherence and the patients' own risk tolerance.

Childhood cancer survivors face markedly worse overall survival after diagnosis with breast cancer, melanoma, or colorectal cancer.

BACKGROUND: Childhood cancer survivors (CCS) are at elevated risk of secondary malignancies (SM). Enhanced screening for SM is recommended, but compliance is poor. We hypothesized that CCS with adult-onset SM (colorectal cancer [CRC], melanoma, or breast cancer [BC]) would present with more advanced disease and have decreased overall survival (OS). METHODS: The Surveillance, Epidemiology, and End Results Program was queried for patients diagnosed with cancer at age less than or equal to 18 also diagnosed with adult-onset CRC, melanoma, or BC. A cohort without a history of prior malignancy was likewise identified. Tumor features and clinical outcomes were compared. RESULTS: CCS with a SM (n = 224) were compared with patients without a childhood cancer history (n = 1,392,670). CCS were diagnosed younger (BC = 37.6 vs. 61.3, p < 0.01, CRC = 35.0 vs. 67.1, p < 0.01, melanoma = 29.6 vs. 61.3 years old, p < 0.01). CCS with BC were more likely to have Stage III or IV disease (25.2% vs. 16.5%, p = 0.01). Hormone-receptor expression also differed; CCS were less likely to develop Luminal A-type tumors (48.6% vs. 66.9%, p = 0.01). After age-adjustment, CCS had worse OS (Hazard ratio: CRC = 2.449, p < 0.01, melanoma = 6.503, p < 0.01, BC = 3.383, p < 0.01). CONCLUSION: CCS were younger when diagnosed with a SM. After age-adjustment, OS was diminished. Heightened surveillance may be necessary for CCS diagnosed with SM.

Predicting adjuvant endocrine therapy initiation and adherence among older women with early-stage breast cancer.

PURPOSE: The CALGB 9343 trial demonstrated that women age 70 or older with early-stage, estrogen receptor positive (ER +) breast cancer (BC) may safely forgo radiation therapy (RT) and be treated with breast conserving surgery followed by adjuvant endocrine therapy (AET) alone. However, most patients in this population still undergo RT in part because AET adherence is low. We sought to develop a predictive model for AET initiation and adherence in order to improve decision-making with respect to RT omission. METHODS: Women ages 70 and older with early-stage, ER + BC were identified using the Surveillance, Epidemiology, and End Results (SEER)-Medicare database. Comorbidities, socioeconomic measures, prescription medications, and demographics were collected as potential predictors. Bivariate analysis was performed to identify factors associated with AET initiation and adherence. Stepwise selection of significant predictors was used to develop logistic regression classifiers for initiation and adherence. Model performance was evaluated using the c-statistic and other measures. RESULTS: 11,037 patients met inclusion criteria. Within the cohort, 8703 (78.9%) patients initiated AET and 6685 (60.6%) were adherent to AET over 1 year. Bivariate predictors of AET initiation were similar to predictors of adherence. The best AET initiation and adherence classifiers were poorly predictive with c-statistics of 0.65 and 0.60, respectively. CONCLUSIONS: The best models in the present study were poorly predictive, demonstrating that the reasons for initiation and adherence to AET are complex and individual to the patient, and therefore difficult to predict. Initiation and adherence to AET are important factors in decision-making regarding whether or not to forgo adjuvant RT. In order to better formulate treatment plans for this population, future work should focus on improving individual prediction of AET initiation and adherence.