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Abstract Background Metaplastic breast cancer (MBC) is a rare and aggressive subtype of breast cancer (BC) defined by presence of both epithelial and mesenchymal components. Most are triple negative but are often chemo-refractory and associated with poor survival outcomes compared to non-metaplastic triple negative BC. Advances in therapy have led to improvements in survival outcomes of patients (pts) with BC over the last decade. Our multicenter retrospective study aims to assess (1) progression free survival (PFS) and overall survival (OS) (2) factors predictive of survival outcomes in MBC pts Methods We performed a retrospective analysis of pts diagnosed with MBC from 1997-2021 at Mayo Clinic (Florida, Arizona and Rochester) under IRB approval. Kaplan-Meier method was used to estimate OS and PFS at 1, 3 and 5 years. Cox regression models were used to examine the association between risk factors and survival outcomes. All tests were two-sided with p value < 0.05 considered statistically significant Results We evaluated 158 pts with MBC. Median age and tumor size was 61 (range: 20-91) years and 2.8 (range: 0.5-21) cm, respectively, with 80% of pts being postmenopausal. At diagnosis, 14.6% of pts had clinical T3/T4 disease, 16.4% were clinically node-positive, and 6.3% (10 pts) had distant metastases (DM). Spindle cell histology was seen in 36 pts. Most MBC pts were triple-negative (68.3%), high grade (77.2%) and high Ki-67 (36/47; 76.5%). Of the 61 pts tested for germline mutation, 8 (13.1%) were positive, with BRCA1/2, PTEN, NBN, CHEK2, and BARD1 mutations. Most pts had lumpectomy (53.8%), followed by simple mastectomy (38.5), and modified radical mastectomy (7.7%). Majority of pts had sentinel lymph node biopsy (71.8%). Adjuvant radiation therapy was performed in 65.6% of pts. Pathologic complete response (pCR) was noted in 4/38 (10.5%) evaluable pts who received neoadjuvant chemotherapy (NACT). Residual cancer burden (RCB) scores of 2 and 3 were seen in 76.2% of evaluable pts. Median follow-up time was 2.2 years (range: 6 days-24.6 years). Overall, 1-, 3-, and 5-year OS was 93.3%, 81.7%, and 76.0%, while PFS was 80.8%, 67.9%, and 60.9%, respectively. The presence of DM at diagnosis [HR 38.55 (11.18, 132.93), p < 0.001] and spindle cell histology (SC) [HR 2.57 (1.19, 5.53), p = 0.02] predicted worse OS in multivariable analysis. Inferior PFS was predicted by DM [HR 18.84 (6.53, 54.35), p < 0.001], SC [HR 2.46 (1.25, 4.86), p = 0.009], and node-positivity at diagnosis [HR 3.65 (1.5, 8.89), p = 0.004]. The 5-year OS and PFS were 22.2% and 0% for DM pts versus 80.0% and 65.6% for non-DM pts. The 5-year OS and PFS were 71.5% and 54.7% for SC pts versus 81% and 66.6% for non-SC pts. 5-year OS and PFS for NACT pts was 67.3% and 52.6% for NACT pts versus 78.2% and 62.8% for non-NACT pts. Age at diagnosis, menopausal status, family history of BC, grade, stage, tumor size, hormone-receptor and HER2 status, and use of NACT were not found to be significantly associated with OS or PFS in multivariate analysis. Conclusion This study is one of the largest and most recent review of institutional experiences with MBC. Overall, OS at 5 years was improved compared to prior older studies of MBC but still remains very low for those with DM, representing an area of unmet clinical need. SC and DM correlated with worse outcomes for both PFS and OS. Additionally, node positivity at diagnosis was a predictor of worse PFS. In contrast, no association was seen between survival and tumor size, stage, hormone receptor-positivity, HER2 receptor-positivity. The low pCR rates following NACT in our study are consistent with reported literature. Further, use of NACT does not impact survival, suggesting pts with resectable disease should proceed with surgery first. Citation Format: Siven Chinniah, Raza Zarrar, Zhuo Li, Kostandinos Sideras, Alvaro Moreno-Aspitia, Saranya Chumsri, Rohit Rao, Sarah McLaughlin, James Jakub, Emmanuel Gabriel, Sanjay Bagaria, Laura Vallow, Santo Maimone, Pooja Advani. Clinical Factors associated with Survival Outcomes in Patients with Metaplastic Breast Cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P3-05-25.

Introduction Contiguous non-mass enhancement (NME) often coexists with a solid tumor component on MRI, but it can be challenging to predict whether NME represents invasive breast cancer, ductal carcinoma in situ (DCIS), benign disease, or biopsy site reaction. The purpose of this study was to determine the association between the size/extent of NME and the presence of invasive cancer and/or DCIS on final pathology. Methods This was a single institution retrospective analysis of a prospectively maintained breast cancer registry (2010-2020). Female patients who underwent surgical resection were included if they had a diagnosis of invasive breast cancer (with or without DCIS) and had an MRI showing both a solid mass and contiguous NME. The size of NME on MRI was compared with the size of invasive cancer and/or DCIS on the final pathology. Results From a total of 3443 patients, 225 patients were included. 86.2% had invasive ductal carcinoma (IDC), and 12.0% had invasive lobular carcinoma 76.9% were ER+, 16.4% were HER2+, and 13.3% were triple negative breast cancer (TNBC). 18.7% received neoadjuvant chemotherapy (NCT) of whom 31% achieved a complete radiographic/pathologic response. Pearson correlation coefficients (r) between the size of NME and invasive cancer/DCIS showed a strong and positive correlation of MRI NME with DCIS on pathology in patients without NCT. Subgroup analysis showed the strongest correlations for NME and DCIS among non-white (r = .70) and HER2 + patients (r = .74) who did not receive NCT. Conclusions Strong correlations between NME and DCIS were found for HER2 + disease and non-white patients, but only modest correlations were found for other patient/disease characteristics. These correlations may impact decisions in surgical approach.

Background: Thirty-six states, including Florida, have legalized marijuana for medical and/or recreational use, yet how it is used and perceived by persons with cancer is not well understood. Objectives: The purpose of this study was to identify patterns of use, perceived benefits, and side effects of medical marijuana (MMJ) among cancer patients in Florida. Methods: For this descriptive, cross-sectional study, anyone residing within the state of Florida who was diagnosed or treated for a malignancy within the last five years and had used MMJ was eligible. An online survey containing questions about dosing, side effects, perceived benefits, and barriers to use was used. Descriptive statistics including frequencies, percentages, means, and standard deviations were used to analyze quantitative data. Responses to open-ended questions were coded and categorized. Results: Sleep ( n = 112), pain ( n = 96), and anxiety ( n = 82) were the most common symptoms participants used MMJ to relieve and overall felt it was highly effective. MMJ was well tolerated with a minority (10.3%) reporting any adverse effects. Cost was the most frequent barrier reported by participants (42.8%). A variety of legal, bureaucratic, and system-related barriers were described. Conclusion: Participants perceived MMJ to be helpful in alleviating cancer symptoms. They held negative perceptions of the way MMJ is implemented and integrated into their oncology treatment plan. Enhanced communication and patient/provider education on MMJ are needed to inform patient decision making.

BNCT is a high LET radiation therapy modality that allows for biologically targeted radiation delivery to tumors while reducing normal tissue impacts. Although the clinical use of BNCT has largely been limited to phase I/II trials and has primarily focused on difficult-to-treat malignancies such as recurrent head and neck cancer and recurrent gliomas, recently there has been a renewed interest in expanding the use of BNCT to other disease sites, including breast cancer. Given its high LET characteristics, its biologically targeted and tumor specific nature, as well as its potential for use in complex treatment settings including reirradiation and widespread metastatic disease, BNCT offers several unique advantages over traditional external beam radiation therapy. The two main boron compounds investigated to date in BNCT clinical trials are BSH and BPA. Of these, BPA in particular shows promise in breast cancer given that is taken up by the LAT-1 amino acid transporter that is highly overexpressed in breast cancer cells. As the efficacy of BNCT is directly dependent on the extent of boron accumulation in tumors, extensive preclinical efforts to develop novel boron delivery agents have been undertaken in recent years. Preclinical studies have shown promise in antibody linked boron compounds targeting ER/HER2 receptors, boron encapsulating liposomes, and nanoparticle-based boron delivery systems. This review aims to summarize the physical and biological basis of BNCT, the preclinical and limited clinical data available to date, and discuss its potential to be utilized for the successful treatment of various breast cancer disease states.

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.

Abstract Background: Endocrine therapy (ET) reduces breast cancer (BC) recurrence risk and improves BC outcomes. However, patients (pts) may refuse ET, potentially impacting their outcomes. However, the exact incidence and factors associated with ET refusal are largely unknown. Methods: We conducted a retrospective study of BC pts in the National Cancer Data Base between 2003 and 2017. Demographic, socioeconomic, co-morbidity index and tumor-specific data were compared between BC pts who refused ET versus those who agreed to ET using bivariate and multivariate models. Female pts 18 to 89 years of age with stage I, II, and III were included. Logistic regression was used to determine associations with ET refusal. Results: Among 463,228 pts, the incidence of ET refusal was 5.26% (24, 401). Of these pts, 85% were non-Hispanic White, 7.9% were Non-Hispanic Black, 3.1% non-Hispanic Asian/pacific islander, and 3.6% were Hispanic. A majority (56.9%) had government insurance, and 87.2% were from a metro residential area. Infiltrating ductal carcinoma BC subtype comprised 78% of pts. Most pts were 51-89 years of age (80%), and 20% were 18-50 years of age. On multivariable analysis (Table 1), non-Hispanic black (OR 0.82), non-Hispanic Asian (OR 0.72), and Hispanic (OR 0.84) pts had a reduced odds of refusing ET than non-Hispanic white pts. Pts with government insurance (OR 1.6, p&lt;0.001) and noninsured pts (OR 1.3, p&lt;0.001) had increased odds of refusing ET compared to privately insured pts. Estrogen receptor (ER) -/Progesterone (PR) +, and ER +/PR - had increased odds of refusing therapy (OR 2.9, and 1.1 respectively, p&lt;0.001) than ER +/PR + pts. Patients with positive lymph nodes had reduced odds of refusing ET than those with negative lymph nodes (p&lt;0.001). Additionally, pts with a 2.1-5 cm (OR 0.92) or &gt;5 cm (OR 0.87) tumor size had a reduced odd of refusing ET than those with tumors less than 2 cm (p&lt;0.001). Finally, patients with well-differentiated BC (grade I) had increased odds of refusing ET (OR 1.2, p&lt;0.001) than moderately differentiated (grade II) BC. Conclusions: The incidence of ET therapy refusal is relatively low; however, survival outcomes may be negatively impacted. This is the first study to evaluate specific demographic and disease-specific factors associated with ET refusal, which can inform strategies to improve ET acceptance rate. Table 1.Multivariable Logistic Regression – ET Therapy Acceptance (Referent) vs. Refusal.VariableOR95% CIp-valueAge51 - 89 years18 - 50 years0.940.900.970.001Race/EthnicityWhite Non-HispanicBlack Non-Hispanic0.820.760.88&lt;0.001Pacific Islander Non-Hispanic0.720.660.76&lt;0.001Hispanic0.840.790.87&lt;0.001InsurancePrivateGovernment1.61.521.61&lt;0.001Not insured1.31.181.47&lt;0.001ResidenceMetroUrban0.900.870.87&lt;0.001Rural0.870.780.970.014HistologyInfiltrating ductal carcinomaLobular carcinoma0.840.800.87&lt;0.001Infiltrating duct and lobular carcinoma0.900.850.95&lt;0.001Others1.171.101.24&lt;0.001Positive Nodes01 - 30.620.600.65&lt;0.0014 - 90.610.570.66&lt;0.00110 +0.610.550.68&lt;0.001VariableOR95% CIp-valueER/PR ExpressionER +/PR +ER -/PR +2.92.563.18&lt;0.001ER +/PR -1.11.061.14&lt;0.001Tumor size≤ 2 cm2.1 - 5 cm0.920.880.94&lt;0.001&gt; 5 cm0.870.800.93&lt;0.001GradeIII1.211.181.25&lt;0.001III0.980.951.020.518Charlson-Deyo Score010.940.910.980.00421.070.991.150.071≥31.120.981.280.079 Citation Format: Pooja P Advani, Ricardo Torres Guzman, Francisco Avila Verduzco, Karla Maita, John Garcia, Abdullah Eldaly, Antonio Forte, Aaron Spaulding. Factors associated with endocrine therapy refusal in hormone receptor-positive breast cancer patients [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P5-14-16.

Abstract Background: SARS-CoV-2 mRNA vaccines have been demonstrated to have robust and durable humoral immune response in healthy individuals. However, their effectiveness in immunocompromised patients, particularly cancer patients, remains less known. Newer data suggests that cancer patients may not mount adequate protective immune response after vaccination. Methods: A retrospective study of patients ≥ 18 years old who had SARS-CoV-2 spike antibody (anti-S Ab) testing after 2 doses of SARS-CoV-2 mRNA vaccines between 12-90 days at Mayo Clinic between January 1, 2021 and May 10, 2021 was performed. The Elecsys Anti-SARS-CoV-2 S electrochemiluminescence immunoassay (Roche Diagnostics, Switzerland) was used to measure the antibody response. Patients with prior COVID-19 infection and patients on immunosuppressive therapy for an indication other than cancer were excluded. Categorical variables were summarized as frequencies (percentages) and continuous variables were reported as median with range. Wilcoxon signed rank test was used to compare continuous variables between groups and Chi-squared or Fisher’s exact test was used to compare categorical variables. All tests were two-sided with p value &lt; 0.05 considered statistically significant. The analysis was done using R program version 3.6.2. Results: Among 201 patients, 79 had breast cancer, 91 had a hematologic malignancy, 6 had other solid malignancies, and 25 had no history of cancer. All breast cancer patients on endocrine therapy or trastuzumab ± pertuzumab without chemotherapy (n=35) had anti-S Ab titer ≥ 500 U/mL. Patients on cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) appeared to have low level of anti-S Ab with 28.6% (n=4/14) had anti-S Ab titer ≤ 500 U/mL. Patients on chemotherapy also had low levels of anti-S Ab with 47% (n=14/30) having anti-S Ab titers ≤ 500 U/mL. When combining breast cancer patients on endocrine therapy alone or anti-HER2 therapy with patients without history of cancer as an immunocompetent group, there was significantly greater proportion of immunocompetent patients (97%) who had anti-S Ab titer ≥ 500 U/mL compared with only 8% of patients with hematologic malignancy and 55% of patients with solid malignancy on chemotherapy or CDK4/6i (p &lt; 0.001). Using multivariate logistic regression analysis adjusted for age, gender, and vaccine type, patients with solid malignancies and treatment-related cytopenia, including chemotherapy and CDK4/6i, (OR 35.51 [95%CI 8.38-255.25, p &lt; 0.001]) were more likely than immunocompetent patients to have a suboptimal anti-S Ab results ≤ 500 U/mL.Conclusion: A significant number of breast cancer patients on chemotherapies and CDK4/6i had poor humoral responses after SARS-CoV-2 mRNA vaccination. While CDK4/6i is not commonly considered as immunosuppressive therapy, breast cancer patients on CDK4/6i appeared to have suboptimal response to SARS-CoV-2 mRNA vaccine. Our study also highlights the significance of assessing antibody response after COVID-19 vaccines in these vulnerable patients. Citation Format: Saranya Chumsri, Pooja P. Advani, Tanmayi S Pai, Zhou Li, Marites Acampora, Gina A Reynolds, Alvaro Moreno-Aspitia, Christopher P Marquez, Keith L. Knutson. Antibody responses after SARS-CoV-2 mRNA vaccination in breast cancer patients [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P3-23-01.

Abstract Background: There is an urgent need to improve clinical trial (CT) enrollment of breast cancer (BC) patients (pts), especially from unrepresented minorities. In this regard, our study aims to better understand the characteristics and factors associated with CT enrollment to inform strategies to enhance CT accrual rates. Method: We included 1,308,767 female pts from the National Cancer Data Base diagnosed from 2010 to 2017 with known ER, PR, and HER2 status. Demographic, socioeconomic, Charlson-Deyo Score (CDS) and BC specific data were compared between CT versus non-CT enrolled pts for initial therapy. Comparisons were assessed by Chi-square test. Logistic regression was utilized to determine associations between characteristics and CT enrollment. Odds ratios (OR) and p-values are reported for each group. Results: A total of 1797 pts (0.14%) were enrolled in CT for initial BC therapy. Focusing on the CT group, majority of pts were non-Hispanic White (W;(78.2%), followed by non-Hispanic black (AA;12.2%); Hispanic (H; 5.6%); and non-Hispanic Asian (A; 4%). Most pts (29.3%) were in 50-59 age quartile. TNBC pts formed 22% of CT pts and non-TNBC were 78%. Most pts were from academic centers (54%), followed by comprehensive community cancer (CCC; 23.5%), community cancer (3.9%) and integrated network cancer (INC; 5.6%) programs. Most had private insurance (70%) versus government insurance (27%) and others (3%). Stage IV pts were only 10% of the CT group while most pts (41%) had Stage II BC. CDS of 0 was noted in 90% pts while 1.3% pts had CDS of 2 or more. Most CT pts traveled &lt; 50 miles from treatment center (88.5%), and only 1.2% CT pts traveled 200 or more miles. Most CT pts resided in areas with highest literacy rate (30%) while 15% were from areas with lowest literacy rate. In multivariable model, non-white pts were less likely than Whites to be enrolled in CT (OR 0.81, p&lt;0.05). The odds of CT enrollment in 40-49, 50-59 and 60-69 age quartiles were 3.5, 2.7 and 2.3 times respectively that of pts 70 years or older (p&lt;0.001). TNBC pts were 1.9 times more likely to be enrolled in CT than non-TNBC pts (p&lt;0.001). Academic center pts were 3 times more likely (p&lt;0.001) while INC program pts were less likely than CCC pts to be enrolled (OR 0.7, p=0.006). Pts with government insurance and other insurance were less likely to enroll in CT (OR 0.74, and 0.55, p &lt;0.001 and p=0.003, respectively) compared to private insurance. The odds of a patient with stage II, III, IV BC enrolling in CT was about 2, 3.5 and 4 times higher than a stage I pt (p -&lt;0.001). Pts with CDS 1 (OR 0.8, p=0.025) or 2 or more (OR 0.5, p=0.002) were less likely than CDS 0 pts to be enrolled. Pts who traveled 50-99 or 100-199 miles from the treatment center conducting CT, were 1.9 (p&lt;0.001) and 1.5 times (p&lt;0.05) more likely to be enrolled while those with &gt; 200 miles were less likely (OR 0.75, p=0.442). The group of pts who belonged to a residential area with the highest literacy rate (&lt;6.3% of no high school diploma) were 1.4 times more likely to accrue in CT (p&lt;0.001) than those with high school diploma rate between 6.3 and 10.8%. Compared to metro areas, pts from rural areas were less likely to be enrolled (OR 0.5, p=0.04) as was a lower median income &lt; $40,227 (OR 0.77, p= 0.016).Conclusion: CT enrollment is poor for initial therapy of BC treatment. We identify several modifiable factors including sociodemographics which are associated with BC pts not getting treated on CT. There are other factors that are non-modifiable, e.g., disease stage but may point to the need for more CT development in these areas. Addressing these disparities would lead to improved CT enrollment and overall advancement in BC management landscape. Citation Format: Pooja P Advani, Aaron Spaulding, Alexander Hochwald, Mizba Baksh, David Hodge, Saranya Chumsri, Shanada Monestime, Sikander Ailawadhi. Clinical trial enrollment for initial therapy of breast cancer: Exploring factors associated with poor accrual and significant disparities [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P2-11-15.