Ruddy, Kathryn J.

Abstract Introduction: Patients at extremes of age may be particularly vulnerable to poor physical and mental health after treatment for breast cancer; we examined factors associated with poor health in older breast cancer survivors. Methods: The Mayo Clinic Breast Disease Registry (MCBDR) is a prospective longitudinal cohort study that enrolls Mayo Clinic Rochester patients diagnosed with stage 0-4 breast cancer (BC). In 2020, we mailed a survey to 1,273 MCBDR participants aged 77+. Three PROMIS-10 items were used to assess overall health, mental health, and physical function. Self-reported comorbidities were also collected. Multivariate logistic regression analysis was used to identify significant (p<0.05) predictors of overall health, mental health, and physical function. Independent variables included demographics, clinical characteristics, and comorbidities. Results: 848/1273 MCBDR participants (67%) responded, 842 reporting their overall health. Median age at survey return was 82 years (range 77-100), and the median time since cancer diagnosis was 12 years. Excellent or very good overall health, mental health, and physical function were reported by 48%, 63.5%, and 77.1%, respectively. Older age was associated with poorer self-reported overall health, as were heart disease, diabetes, and lung disease, reported by 18%, 14%, and 7%, respectively (p<0.05 for all; see Table). Only heart disease was statistically significantly associated with poorer mental health (p=0.03). Physical function was reportedly better in survivors without a history of diabetes, stroke, or lung disease (p<0.05 for all), and in those who were closer to their cancer diagnosis (p=0.03). Tumor characteristics were not associated with overall health, mental health, or physical function. Conclusions: Comorbidities are common and impact self-reported overall health, mental health, and physical function in older breast cancer survivors. Table: Multivariate logistic regression model for overall health Overall health self-reported as excellent or very good No Yes Total p-value (N=437) (N=405) (N=842) Age at survey (years) <.001 Mean (SD) 82.8 (4.22) 81.7 (3.85) 82.3 (4.08) Median (range) 82.0 (77.0, 96.0) 81.0 (77.0, 100.0) 82.0 (77.0, 100.0) Years from cancer diagnosis to survey 0.708 Mean (SD) 12.1 (5.16) 11.8 (5.47) 11.9 (5.31) Median (range) 12.2 (3.1, 36.9) 11.5 (3.1, 36.4) 12.0 (3.1, 36.9) T stage T2 or higher, n (%) 0.276 No 357 (81.7%) 337 (83.2%) 694 (82.4%) Yes 80 (18.3%) 68 (16.8%) 148 (17.6%) N stage N1 or higher, n (%) 0.185 No 376 (86.0%) 339 (83.7%) 715 (84.9%) Yes 61 (14.0%) 66 (16.3%) 127 (15.1%) M stage M1, n (%) 0.313 No 434 (99.3%) 404 (99.8%) 838 (99.5%) Yes 3 (0.7%) 1 (0.2%) 4 (0.5%) Race, n (%) 0.460 Non-White 13 (3.0%) 8 (2.0%) 21 (2.5%) White 424 (97.0%) 397 (98.0%) 821 (97.5%) Heart disease, n (%) <.001 No 334 (76.4%) 353 (87.2%) 687 (81.6%) Yes 103 (23.6%) 52 (12.8%) 155 (18.4%) High blood pressure, n (%) 0.376 No 168 (38.4%) 188 (46.4%) 356 (42.3%) Yes 269 (61.6%) 217 (53.6%) 486 (57.7%) Stroke, n (%) 0.195 No 407 (93.1%) 392 (96.8%) 799 (94.9%) Yes 30 (6.9%) 13 (3.2%) 43 (5.1%) Diabetes, n (%) <.001 No 355 (81.2%) 370 (91.4%) 725 (86.1%) Yes 82 (18.8%) 35 (8.6%) 117 (13.9%) Lung disease, n (%) 0.023 No 394 (90.2%) 386 (95.3%) 780 (92.6%) Yes 43 (9.8%) 19 (4.7%) 62 (7.4%) Liver disease, n (%) 0.345 No 425 (97.3%) 401 (99.0%) 826 (98.1%) Yes 12 (2.7%) 4 (1.0%) 16 (1.9%) Kidney disease, n (%) 0.240 No 408 (93.4%) 392 (96.8%) 800 (95.0%) Yes 29 (6.6%) 13 (3.2%) 42 (5.0%) Citation Format: Dhauna Karam, Robert A. Vierkant, Shawna Ehlers, Rachel A. Freedman, Nicole Larson, Charles L. Loprinzi, Fergus Couch, Janet Olson, Kathryn J. Ruddy. Physical function, mental health, and overall health of older breast cancer survivors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5262.

Abstract BACKGROUND: The American Cancer Society recommends at least 150 minutes of moderate and/or strenuous exercise and muscle-strengthening activities each week for adults. Exercise has been associated with decreased breast cancer mortality and adverse symptoms. This study’s purpose is to understand prevalence and predictors of inadequate aerobic exercise in patients recently diagnosed with breast cancer to inform interventions to increase exercise participation. METHODS: Patients seen at least once at Mayo Clinic Rochester were prospectively enrolled within one year of an initial breast cancer diagnosis in the Mayo Clinic Breast Disease Registry after providing informed consent. This analysis includes those who completed a baseline survey with self-reported exercise data using the Godin Leisure-Time Exercise Questionnaire. This longitudinal cohort study was approved by the Mayo Clinic institutional review board. RESULTS: 1,738 participants reported their usual weekly quantity of moderate and strenuous exercise an average of 95 days (SD 71 days, range 0-365) after diagnosis. Table 1 displays participant characteristics overall and by whether participants reported at least 150 minutes of moderate and/or strenuous activity weekly (“met guidelines”) or not (“did not meet guidelines”). Overall, 39% of participants met guidelines, including 56% of those aged 18-39 years, 40% of those aged 40-69 years, and 27% of those aged 70+ years. CONCLUSION: Older age was associated with less likelihood of meeting exercise guidelines (all age groups vs 70+, p < 0.05). A more diverse cohort will be needed to evaluate differences by gender and race/ethnicity. There did not appear to be any obvious impact on exercise level by time since diagnosis (during the first year after diagnosis) or educational status, though substantial missing data limit conclusions related to the latter. Additional research is needed to assess exercise levels later in survivorship and the impact of various treatment modalities on exercise habits Table 1. Patient and tumor characteristics Citation Format: Paulina S. Marell, Janet E. Olson, Joerg Herrmann, Nicole L. Larson, Nathan K. LeBrasseur, Stacy D. D'Andre, Andrea L. Cheville, Toure Barksdale, Charles L. Loprinzi, Fergus J. Couch, Kathryn J. Ruddy. Factors associated with exercise participation in patients with breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5868.

Abstract Background: Medical financial hardship, encompassing material, behavioral, and psychologic domains, is becoming an increasingly common consequence of illness in cancer patients. Identifying at-risk patients is the first step to develop proactive approaches to mitigate this problem. To try and address this need, Mayo Clinic Breast Disease Registry (MCBDR) is prospectively collecting data about financial concerns in addition to the usual sociodemographic and clinical information. Methods: We used data from Mayo Clinic Breast Disease Registry, a prospective cohort of consenting patients seen at Mayo Clinic Rochester within one year of initial breast cancer diagnosis. Participants completed baseline and annual follow-up surveys rating their financial concerns on a linear analogue scale from 0 (“none”) to 10 (“constant concerns”). We compared patient-reported financial concern at baseline to that on each patient’s most recent survey, with worsening concerns defined as a 1+-point increase. Logistic regression evaluated for predictors of worsening financial concerns. Results: 1,957 participants responded to financial concern questions on a baseline and at least one follow-up survey between 2015 and 2020. Mean age was 58.5 years (SD 12.5), and mean time between diagnosis and the most recent follow-up was 25.6 months (SD 16.2). 357 (18.2%) reported worsening financial concerns. Only lower baseline financial status was associated with a greater likelihood of worsening financial concerns (see Table). Conclusions: More than one in seven breast cancer survivors develop worsening financial concerns within 5-years of diagnosis, and those with less financial security at baseline appear to be most vulnerable. Funding: Breast Cancer Research Foundation (CLL) and NR015259 (KJR). Patient and tumor characteristics, compared by whether financial status worsened over time Full Cohort (n=1957) Worsening, ≥ 1-point change (n=357) Stable/Improved (n=1600) p value Full Cohort (n=1957) Worsening, ≥ 1-point change (n=357) Stable/Improved (n=1600) p value Age at diagnosis II or III 502 (25.7%) 98 (27.5%) 404 (25.3%) 0.239 ≤ 50 546 (27.9%) 105 (29.4%) 441 (27.6%) IV 67 (3.4%) 17 (4.8%) 50 (3.1%) 0.086 51-64 757 (38.7%) 136 (38.1%) 621 (38.8%) 0.562 Unknown 351 (17.9%) 65 (18.2%) 286 (17.9%) 0.536 ≥65 654 (33.4%) 116 (32.5%) 538 (33.6%) 0.506 ER and/or PR positive Race No/Unknown 482 (24.6%) 92 (25.8%) 390 (24.4%) White 1863 (95.2%) 337 (94.4%) 1526 (95.4%) Yes 1475 (75.4%) 265 (74.2%) 1210 (75.6%) 0.580 Non-white 24 (1.2%) 5 (1.4%) 19 (1.2%) 0.729 Her2 positive Other/Unknown/Choose not to respond 70 (3.6%) 15 (4.2%) 55 (3.4%) 0.478 No/Unknown 1746 (89.2%) 314 (88.0%) 1432 (89.5%) Educational status Yes 176 (9.0%) 37 (10.4%) 139 (8.7%) 0.321 Less than bachelor’s degree 880 (45.0%) 168 (47.1%) 712 (44.5%) Borderline 35 (1.8%) 6 (1.7%) 29 (1.8%) 0.898 Bachelor's degree or higher 1065 (54.4%) 187 (52.4%) 878 (54.9%) 0.384 Radiation Unknown 12 (0.6%) 2 (0.6%) 10 (0.6%) 0.832 No/Unknown 781 (39.9%) 140 (39.2%) 641 (40.1%) Financial status near time of diagnosis Yes 1176 (60.1%) 217 (60.8%) 959 (59.9%) 0.768 Pay bills, money for special things 1412 (72.2%) 244 (68.3%) 1168 (73.0%) Chemotherapy/targeted therapy Pay bills, no money for special things 367 (18.8%) 80 (22.4%) 287 (17.9%) 0.046 No/Unknown 1264 (64.6%) 221 (61.9%) 1043 (65.2%) Pay bills by making cuts 102 (5.2%) 19 (5.3%) 83 (5.2%) 0.729 Yes 693 (35.4%) 136 (38.1%) 557 (34.8%) 0.241 Unable to pay bills 56 (2.9%) 10 (2.8%) 46 (2.9%) 0.911 Hormone/endocrine therapy Unknown 20 (1.0%) 4 (1.1%) 16 (1.0%) 0.750 No/Unknown 710 (36.3%) 141 (39.5%) 569 (35.6%) Employment status at time of diagnosis Yes 1247 (63.7%) 216 (60.5%) 1031 (64.4%) 0.163 Employed full-time 462 (23.6%) 83 (23.2%) 379 (23.7%) Surgery type Employed part-time/unemployed/retired 525 (26.8%) 92 (25.8%) 433 (27.1%) 0.856 Lumpectomy 846 (43.2%) 145 (40.6%) 701 (43.8%) Not available 970 (49.6%) 182 (51.0%) 788 (49.3%) 0.716 Mastectomy 903 (46.1%) 165 (46.2%) 738 (46.1%) 0.535 Stage at time of diagnosis None/Unknown 208 (10.6%) 47 (13.2%) 161 (10.1%) 0.069 0 or I 1037 (53.0%) 177 (49.6%) 860 (53.8%) Citation Format: Michael H. Storandt, Urshila Durani, Daniela Stan, Nicole Larson, Charles Loprinzi, Fergus Couch, Janet E. Olson, Nandita Khera, Kathryn J. Ruddy. Financial hardship in breast cancer survivors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1012.

e24094 Background: Hundreds, if not thousands, of participants are enrolled hot flash trials each year given the magnitude of the problem for breast and prostate cancer survivors. Classically, these studies have included a baseline period of 1-week, or longer, to understand the frequency and severity of hot flashes before starting a new treatment. The objective of the current study was to compare the accuracy of a 1-day baseline hot flash diary to a more traditional 1-week dairy. A shorter baseline period would be more convenient for patients and provide a more efficient study design. Methods: Raw data from 5 pilot studies and 15 phase III randomized, controlled trials (RCTs), all of which used a one-week baseline period, were obtained. Descriptive statistics were used to describe day-by-day variations in hot flash frequencies and scores, during the baseline week. Additional analyses evaluated whether the conclusions from any of the individual pilot studies would have been changed if only a 1-day baseline period had been used. For the RCTs, p-values were recalculated using mixed models, adjusting for the baseline value by including it as a covariate. Results: A total of 2,573 participants were included. On average, participants had 8.5 hot flashes per day on Day 1. Mean hot flash frequencies and scores on subsequent days (Days 2-7) were within 6% of Day 1 values. When comparing a 1-day to a 1-week baseline period, there was an absolute difference of only 0.29 hot flashes per day (SD 2.25). Re-analysis for each pilot study revealed that no individual study conclusions would have been meaningfully altered by a shorter baseline. For the RCTs, a shorter baseline period changed the results of only 1 of 24 comparisons from statistically significant to not significant, or vice versa. Conclusions: A 1-day hot flash diary appears to accurately reflect true frequency and severity of baseline hot flash symptoms in appropriately sized cohorts. Results support a shorter baseline period for pilot studies and RCTs.

12107 Background: Chemotherapy-induced nausea and vomiting (CINV), a major adverse effect of cancer treatment, can attenuate life quality. Multiple international antiemetic guidelines have recommended a 4-drug regimen (corticosteroid, 5-HT3 receptor antagonist, NK-1 receptor antagonist, and the antipsychotic medication olanzapine) for decreasing highly emetogenic CINV. This raised a question regarding whether antiemetic therapy regimens for highly emetogenic chemotherapy could be de-intensified, decreasing cost and side effects from anti-emetogenic agents. Methods: Study A221602 was developed to compare two olanzapine-containing antiemetic regimens, one with the use of an NK-1 receptor antagonist (aprepitant or fosaprepitant) and one without. Patients (pts) received intravenous highly emetogenic chemotherapy as either 1) cisplatin, given on one day, at a dose of ≥ 70 mg/m2, with or without other chemotherapy agent(s) or 2) doxorubicin (60 mg/m2) plus cyclophosphamide (600 mg/m2) on one day. Pts in both arms received 1) a 5-HT3 receptor antagonist (palonosetron 0.25 mg IV or ondansetron 8-16 mg IV or 16-24 mg PO,) on day one, 2) dexamethasone (12 mg PO, day one followed by 8 mg PO, days 2-4), and 3) olanzapine (10 mg/day PO, days 1 to 4). On Day 1, all agents were given prior to chemotherapy, with the exception that olanzapine could be taken prior to chemotherapy or at bedtime. Additionally, pts were randomized to receive an NK-1 receptor antagonist (fosaprepitant 150 mg IV or aprepitant 130 mg IV; 346 pts) or a matching placebo (344 pts). The primary objective was to compare the proportion of patients with no nausea for 5 days following receipt of their chemotherapy between the two study arms. Results: While there was no suggestion of outcome differences on day 1 between the two study arms, fewer pts (7.4%; upper limit of the 95% confidence interval was 13.5%) without NK-1 receptor antagonists were without nausea for the complete 5-day study period. Conclusions: Per the study design, created to exclude a 10% benefit for NK-1 receptor antagonists, the results did not provide sufficient evidence to reject the hypothesis that the 4-drug regimen was superior to the protocol 3-drug regimen (p=0.24). Support: UG1CA189823; Clinical trial information: NCT03578081.

10607 Background: Young women with breast cancer who carry germline genetic pathogenic variants predisposing to breast and other cancers, including BRCA1 or BRCA2, may face unique challenges when making fertility decisions. Limited data exist on differences in fertility preferences, concerns, and preservation strategies between carriers and non-carriers. Methods: Participants in the Young Women’s Breast Cancer Study, a prospective cohort of women diagnosed with breast cancer at ≤ 40 yrs, who completed a baseline survey with a modified Fertility Issues Survey were included in this analysis. Genetic variant status was determined by medical record review complemented by survey self-report. We excluded carriers whose test date was after baseline survey completion or unknown. Fisher exact and Wilcoxon signed-rank tests were used to compare categorical and continuous variables, respectively, between carriers and non-carriers. Results: Of 1052 eligible women, 118 (11%) tested positive for a pathogenic variant (59% BRCA1, 32% BRCA2, 4% TP53, and 5% other unique pathogenic mutations) and 934 (89%) tested negative or were not tested. Carriers’ median age was 36 yrs (range 23-40) vs 37 (range 17-40, p = 0.01) in non-carriers. Similar proportions (p = 0.67) of carriers (38%, [45/118]) and non-carriers (37%, [343/934]) desired more biologic children before diagnosis. Desire declined after diagnosis similarly in both groups (carriers, 25% [29/118] vs non-carriers, 26% [242/934], p = 0.46). Among these women (n = 271), concern about passing on cancer risk to offspring was common and, although numerically higher among carriers, this difference was not statistically significant (carriers, 55% [16/29] vs non-carriers, 40% [96/242], p = 0.12). In contrast, among those not interested in or unsure about future fertility (n = 738), concern about cancer risk heritability was infrequently reported as affecting fertility decisions (carriers, 11% [9/83] vs non-carriers, 9% [56/655], p = 0.54). The same proportions (p = 0.89) of carriers (36% [43/118]) and non-carriers (36% [339/934]) were somewhat or very concerned about becoming infertile after cancer treatment, and fertility preservation strategy utilization was similar between groups (carriers, 11% [13/118] vs non-carriers, 12% [111/934], p = 0.21). Conclusions: Young women with breast cancer who carry germline pathogenic variants are similarly concerned about future fertility and as likely to pursue fertility preservation as non-carriers. Concern about cancer risk heritability was common among both carriers and non-carriers desiring future fertility, suggesting a gap between perceived and actual risk. Genetic counseling should be included in fertility discussions for all young women with breast cancer, with tailored, risk-mitigating recommendations for those who carry genetic variants.

TPS610 Background: Several studies demonstrated worsening disease-free survival in patients who failed to achieve complete pathological response after neoadjuvant chemotherapy (NAC), particularly in HER2-positive (HER2+) breast cancer. Despite the recent approval of trastuzumab emtansine (T-DM1) in patients with residual disease after NAC approximately 12% of patients still develop recurrent and metastatic disease. TPIV100 is a multi-epitope vaccine that includes a pool of 4 degenerate HER2-derived HLA-DR epitopes, which activate CD4 helper T cells, admixed with GM-CSF. In our previous phase I trial this vaccine was shown to be safe in combination with trastuzumab in stage II-III HER2+ breast cancer after completion of standard of care chemotherapy. Furthermore, this vaccine also generated robust long-lasting T-cell immune responses and antibody immunity against HER2. Methods: This trial is a multi-center, randomized, placebo-controlled, phase II trial of TPIV100 in combination with T-DM1 in stage II-III HER2+ breast cancer patients with residual disease after NAC. This trial is currently opened through the ACCRU consortium. Eligible patients include those with stage II-III HER2+ with residual disease, in the breast and/or lymph nodes, after trastuzumab ± pertuzumab-based NAC, with ECOG PS ≤ 2 and adequate organ function. Patients with baseline left ventricular ejection fraction < 50%, history of trastuzumab-related cardiac toxicity, myocardial infarction or stroke < 6 months, history of congestive heart failure, autoimmune disease, immunocompromised patients with known HIV or those on chronic steroid, hypersensitivity to GM-CSF, and other active malignancy < 3 years are excluded. TPIV100 or placebo, in combination with GM-CSF, will be given concurrently with T-DM1. To ensure that TPIV100 in combination with T-DM1 is safe, there is a run-in phase with 20 patients treated with the combination. If there is no significant dose-limiting toxicity observed in the run-in phase, the trial will be expanded to the randomized phase II portion, which will include 240 patients. Eligible patients will be randomized in a 2:1 fashion with ER/PR as a stratification factor. The primary endpoint is invasive disease-free survival, and the secondary endpoint includes immunogenicity of TPIV100 as assessed by IFN-g ELIspot analysis. Correlative studies include assessment of helper T-cell response distribution (including Th1, Th2, Th17, Tfh), HER2-specific antibody immunity, and HLA genotype. Currently, 20 patients in the run-in phase have been enrolled. Enrollment to the randomized phase II portion is expected to begin in March 2022. Clinical trial information: NCT04197687.

555 Background: Women with early-stage breast cancer (BCa) are living longer, and survivorship issues including second primary cancers (SPCs) are therefore increasingly important. This study seeks to determine the risk of SPCs, including contralateral breast cancer (CBCa), in women with early-stage invasive lobular carcinoma (ILC). Methods: The study population consisted of women with BCa diagnosis between 2000-2018 within the NCI Surveillance, Epidemiology, and End Results (SEER v 3.2.9) registry and between 2000-2021 in the Mayo Clinic Cancer Registry. In the SEER registry, the standardized incidence ratios (SIR) for SPCs were estimated for adult women with histologically confirmed early stage (I-III) ILC compared to the development of any primary cancer in the general population. For reference, SIRs for SPCs for a similar patient population with invasive ductal carcinoma (IDC) of the breast were also estimated. For comparison of CBCa between ILC and IDC, follow up records from the Mayo Clinic Cancer Registry were evaluated among adult women who underwent lumpectomy or unilateral mastectomy for early stage ILC or IDC. A multivariable Cox proportional hazards regression was performed to compare the risk of CBCa between ILC and IDC while adjusting for the age at diagnosis, race/ethnicity and estrogen receptor status of the primary tumor. Results: An increased incidence (p<0.05) of any SPCs and second BCa was noted for both ILC and IDC compared to the expected rate of primary cancer in the general population (Table). Interestingly, women with ILC were observed to have a significantly increased incidence of subsequent gastric cancer which was not seen for women with IDC. An SIR >1.5 was noted for subsequent risk of sarcoma, myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML) for both ILC and IDC (Table). In the Mayo Clinic Cancer Registry of 2,218 women with ILC and 14,629 women with IDC meeting the inclusion criteria, the 5-year risk of CBCa was 2.6% and 1.5% (log rank statistic p-value =0.001) for ILC and IDC respectively. A significantly increased risk of CBCa was noted in women with ILC (Hazard Ratio 1.82, 95% CI 1.34-2.47, p<0.001) compared to women with IDC in the multivariable analysis. Conclusions: Women with ILC may have an increased risk of SPC and second BCa compared to the risk of any primary cancer in the general population. The increased incidence of gastric cancer and the higher risk of CBCa in ILC survivors compared to women with IDC is intriguing and needs to be investigated further including evaluation of the role of germline genetic factors. [Table: see text]

524 Background: OFS is an important treatment component for premenopausal women with early and advanced HR+ BC and optimal efficacy may depend on complete E2 suppression with GnRHa, especially when combined with aromatase inhibitors (AI). However, standard assays lack sensitivity and accuracy at very low E2 concentrations, rendering detection of breakthrough ovarian function challenging. More informative data regarding endocrine effects of GnRHa are needed, particularly in young women who derive the most benefit from OFS yet more frequently had breakthrough E2 levels in the SOFT trial substudy, SOFT-EST. Methods: Using a prospective cohort study of women with BC diagnosed at age ≤ 40 years, we identified participants with stage I-IV HR+ BC on OFS treatment with leuprolide, goserelin or triptorelin and blood collected 1 year after diagnosis. Clinical data were obtained through surveys and medical records. Plasma estrogens were measured by liquid chromatography-tandem mass spectrometry, with a limit of detection of 0.2 pg/mL compared to 10 pg/mL with standard assays. We assessed the proportion of women on OFS with E2 > 2.72 pg/mL (10 pmol/L) and > 10 pg/mL. Patient characteristics, estrone (E1) and FSH levels, and disease-free (DFS) and overall survival (OS) were compared between those with and without elevated E2 using Fischer’s exact, Wilcoxon rank sum and log rank tests, respectively. Results: Of 84 patients who met inclusion criteria, 72 (86%) had stage I-III and 12 (14%) had stage IV BC; 25 were on OFS plus AI and 59 were on OFS plus tamoxifen (TAM). Median E2 was 3.1 pg/mL (range 0.2-30.9). 46 patients (55%) had E2 > 2.72 pg/mL, including 8 on AI and 38 on TAM; 4 (5%) had E2 > 10 pg/mL, including 1 on AI and 3 on TAM. Factors associated with E2 > 2.72 pg/mL were no prior chemotherapy, TAM and high E1 ( P ≤.05), but not age, BMI or GnRHa schedule (Table). After a median follow-up of 7 years, DFS events were seen in 6 patients with E2 > 2.72 pg/mL and 5 without ( P =.232); OS events were seen in 7 patients with E2 > 2.72 pg/mL and 5 without ( P =.608). Conclusions: More than half of young women with ER+ BC had E2 > 2.72 pg/mL on OFS, 91% of whom would not have been detected by standard assays. This may be an area amenable to intervention to improve outcomes in young women. However, larger studies are needed to elucidate the optimal E2 target on OFS and clinical implications of incomplete E2 suppression on ultrasensitive assays. [Table: see text]

Abstract Purpose Cyclin dependent kinase 4/6 inhibitors (CDK4/6is), in combination with endocrine therapy (ET), are standard either in the first (1L) or second line (2L) setting for the treatment of hormone receptor (HR) positive, HER2-negative metastatic breast cancer (MBC). However, the optimal sequencing of treatments after progression on CDK4/6i remains unknown. We performed a single institution analysis to identify treatments and outcomes after progression on a CDK4/6i. Methods We identified patients with HR-positive, HER2-negative MBC prescribed a CDK4/6i in the 1L or 2L settings from December 2014-February 2018 at Mayo Clinic in Rochester, Minnesota. Outcomes were collected through September 30, 2020. Results Palbociclib, in combination with letrozole or fulvestrant, was the most prescribed CDK4/6i. The 1L and 2L CDK4/6i cohorts exhibited comparable overall survival (OS), but progression free survival (PFS) was longer in the 1L than the 2L cohort [28.2 months (95% CI 19.6–34.9) vs 19.8 months (95% CI 15.7–29.6)]. The most common post-CDK4/6i treatments were PI3K/mTOR inhibitors (PI3K/mTORi), single agent ET, or chemotherapy. PFS in the 1L CDK4/6i cohort following PI3K/mTORi was 8.5 months (95% CI 5.5 months – NE), single-agent ET was 6.0 months (95% CI 3.3–14.0 months), and chemotherapy PFS was 5.4 months (95% CI 3.3 months- NE). Conclusions Following progression on a CDK 4/6i, mPFS was short, with similar PFS times comparing chemotherapy and ET, with slightly longer PFS for targeted strategies (PI3K/mTOR). These results highlight a major need to better understand the mechanisms of CDK4/6i resistance and identify new therapeutic strategies for these patients.