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Associations of Genetically Predicted Lp(a) (Lipoprotein [a]) Levels With Cardiovascular Traits in Individuals of European and African Ancestry
Satterfield, Benjamin A. , Dikilitas, Ozan , Safarova, Maya , Clarke, Shoa L. , Tcheandjieu, Catherine , Zhu, Xiang , Bastarache, Lisa , Larson, Eric B. , Justice, Anne E. , Shang, Ning , Rosenthal, Elisabeth A. , Namjou‐Khales, Bahram, Wei, Wei‐Qi, Feng, QiPing , Jarvik, Gail P. , Hebbring, Scott J. , Manolio, Teri A. , Assimes, Themistocles L. , Safarova, Maya S, Jarvik, Gail P , Dikilitas, Ozan , Wei, Wei-Qi , Clarke, Shoa L , Assimes, Themistocles L , Satterfield, Benjamin A , Feng, Qiping , Shah, Amy S. , Urbina, Elaine M. , Andrade, Mariza de , Kullo, Iftikhar J.

Circulation: Genomic and Precision Medicine | July 20, 2021 | Volume: 14 | Issue: 4 | Pages: No page available

10.1161/circgen.120.003354 | PMID 34282949 Get It

Background: Lp(a) (lipoprotein [a]) levels are higher in individuals of African ancestry (AA) than in individuals of European ancestry (EA). We examined associations of genetically predicted Lp(a) levels with (1) atherosclerotic cardiovascular disease subtypes: coronary heart disease, cerebrovascular disease, peripheral artery disease, and abdominal aortic aneurysm and (2) nonatherosclerotic cardiovascular disease phenotypes, stratified by ancestry. Methods: We performed (1) Mendelian randomization analyses for previously reported cardiovascular associations and (2) Mendelian randomization–phenome-wide association analyses for novel associations. Analyses were stratified by ancestry in electronic Medical Records and Genomics, United Kingdom Biobank, and Million Veteran Program cohorts separately and in a combined cohort of 804 507 EA and 103 580 AA participants. Results: In Mendelian randomization analyses using the combined cohort, a 1-SD genetic increase in Lp(a) level was associated with atherosclerotic cardiovascular disease subtypes in EA—odds ratio and 95% CI for coronary heart disease 1.28 (1.16–1.41); cerebrovascular disease 1.14 (1.07–1.21); peripheral artery disease 1.22 (1.11–1.34); abdominal aortic aneurysm 1.28 (1.17–1.40); in AA, the effect estimate was lower than in EA and nonsignificant for coronary heart disease 1.11 (0.99–1.24) and cerebrovascular disease 1.06 (0.99–1.14) but similar for peripheral artery disease 1.16 (1.01–1.33) and abdominal aortic aneurysm 1.34 (1.11–1.62). In EA, a 1-SD genetic increase in Lp(a) level was associated with aortic valve disorders 1.34 (1.10–1.62), mitral valve disorders 1.18 (1.09–1.27), congestive heart failure 1.12 (1.05–1.19), and chronic kidney disease 1.07 (1.01–1.14). In AA, no significant associations were noted for aortic valve disorders 1.08 (0.94–1.25), mitral valve disorders 1.02 (0.89–1.16), congestive heart failure 1.02 (0.95–1.10), or chronic kidney disease 1.05 (0.99–1.12). Mendelian randomization–phenome-wide association analyses identified novel associations in EA with arterial thromboembolic disease, nonaortic aneurysmal disease, atrial fibrillation, cardiac conduction disorders, and hypertension. Conclusions: Many cardiovascular associations of genetically increased Lp(a) that were significant in EA were not significant in AA. Lp(a) was associated with atherosclerotic cardiovascular disease in four major arterial beds in EA but only with peripheral artery disease and abdominal aortic aneurysm in AA. Additionally, novel cardiovascular associations were detected in EA.
Risk of pulmonary emboli after removal of an upper extremity central catheter associated with a deep vein thrombosis
Houghton, Damon E. , Billett, Henny H., Gaddh, Manila , Onadeko, Oluwatomiloba , George, Gemlyn , Wang, Tzu‐Fei , Oo, Thein Hlaing , Feng, Mingen, Dasgupta, Mahua , Streiff, Michael B. , Simpson, Pippa , Gali, Radhika, Billett, Henny Heisler , Oo, Thein H , Streiff, Michael B , Baumann Kreuziger, Lisa , Houghton, Damon E , Jaglal, Michael Vishal , Kreuziger, Lisa Baumann

Blood Advances | July 15, 2021 | Volume: 5 | Issue: 14 | Pages: 2807-2812

10.1182/bloodadvances.2021004698 | PMID 34264267 Get It

Abstract Standard treatment of catheter-associated upper extremity deep vein thrombosis (UE-DVT) is anticoagulation, although catheters are often removed for this indication. The optimal time for catheter removal and whether the act and/or timing of catheter removal is associated with pulmonary embolism (PE) remain unknown. A retrospective cohort study was performed at 8 participating institutions through the Venous thromboEmbolism Network US. Patients with hematologic malignancies and central venous catheter (CVC)–associated UE-DVT were included from 1 January 2010 through 31 December 2016. The primary outcome was objectively confirmed PE within 7 days of UE-DVT diagnosis in anticoagulated patients comparing early (≤48 hours) vs delayed (>48 hours) catheter removal. A total of 626 patients were included, among whom 480 were treated with anticoagulation. Among anticoagulated patients, 255 underwent early CVC removal, while 225 had delayed or no CVC removal; 146 patients received no anticoagulation, among whom 116 underwent CVC removal alone. PE within 7 days occurred in 2 patients (0.78%) with early removal compared with 1 patient (0.44%) with delayed or no CVC removal (P > .9). PE or any cause of death within 7 days occurred in 3 patients in both the early removal (1.18%) and delayed/no removal (1.33%) groups (P > .9). In patients treated with CVC removal only (no anticoagulation), there were no PEs but 3 deaths within 7 days. In patients with hematological malignancy and CVC-associated UE-DVT, early removal of CVCs was not associated with an increased risk of PE compared with delayed or no removal.
Metabolic Enzyme DLST Promotes Tumor Aggression and Reveals a Vulnerability to OXPHOS Inhibition in High-Risk Neuroblastoma
Anderson, Nicole , Qin, Xiaodan , Finan, Jennifer M. , Lam, Andrew , Athoe, Jacob, Missiaen, Rindert , Skuli, Nicolas , Kennedy, Annie, Saini, Amandeep S. , Tao, Ting , Zhu, Shizhen , Nissim, Itzhak , Look, A. Thomas , Qing, Guoliang , Simon, M. Celeste , Feng, Hui , Tao, Ting , Anderson, Nicole M., Kennedy, Annie

Cancer Research | July 7, 2021 | Volume: 81 | Issue: 17 | Pages: 4417-4430

10.1158/0008-5472.can-20-2153 | PMID 34233924 Get It

Abstract High-risk neuroblastoma remains therapeutically challenging to treat, and the mechanisms promoting disease aggression are poorly understood. Here, we show that elevated expression of dihydrolipoamide S-succinyltransferase (DLST) predicts poor treatment outcome and aggressive disease in patients with neuroblastoma. DLST is an E2 component of the α-ketoglutarate (αKG) dehydrogenase complex, which governs the entry of glutamine into the tricarboxylic acid cycle (TCA) for oxidative decarboxylation. During this irreversible step, αKG is converted into succinyl-CoA, producing NADH for oxidative phosphorylation (OXPHOS). Utilizing a zebrafish model of MYCN-driven neuroblastoma, we demonstrate that even modest increases in DLST expression promote tumor aggression, while monoallelic dlst loss impedes disease initiation and progression. DLST depletion in human MYCN-amplified neuroblastoma cells minimally affected glutamine anaplerosis and did not alter TCA cycle metabolites other than αKG. However, DLST loss significantly suppressed NADH production and impaired OXPHOS, leading to growth arrest and apoptosis of neuroblastoma cells. In addition, multiple inhibitors targeting the electron transport chain, including the potent IACS-010759 that is currently in clinical testing for other cancers, efficiently reduced neuroblastoma proliferation in vitro. IACS-010759 also suppressed tumor growth in zebrafish and mouse xenograft models of high-risk neuroblastoma. Together, these results demonstrate that DLST promotes neuroblastoma aggression and unveils OXPHOS as an essential contributor to high-risk neuroblastoma. Significance: These findings demonstrate a novel role for DLST in neuroblastoma aggression and identify the OXPHOS inhibitor IACS-010759 as a potential therapeutic strategy for this deadly disease.
Critically Ill Patients Treated for Chimeric Antigen Receptor-Related Toxicity: A Multicenter Study*
Gutierrez, Cristina, Brown, Anne Rain T., May, Heather P., Beitinjaneh, Amer, Stephens, R. Scott, Rajendram, Prabalini, Nates, Joseph L., Pastores, Stephen M., Dharshan, Ananda, Moraes, Alice Gallo de, Hensley, Matthew K., Feng, Lei, Brudno, Jennifer N., Athale, Janhavi, Ghosh, Monalisa, Kochenderfer, James N., Arias, Alejandro S., Lin, Yi, McEvoy, Colleen, Mead, Elena, Westin, Jason, Kostelecky, Natalie, Mian, Agrima, Herr, Megan M., Lin, Yi , Beitinjaneh, Amer , Kochenderfer, James N. , Brown, Anne Rain , De Moraes, Alice Gallo, Lin, Yi , Gutierrez, Cristina, Brown, Anne Rain T., May, Heather P., Stephens, R. Scott, Rajendram, Prabalini, Nates, Joseph L., Pastores, Stephen M., Dharshan, Ananda, Moraes, Alice Gallo de, Hensley, Matthew K., Feng, Lei, Brudno, Jennifer N., Athale, Janhavi, Ghosh, Monalisa, Arias, Alejandro S., Lin, Yi, McEvoy, Colleen, Mead, Elena, Westin, Jason, Kostelecky, Natalie, Mian, Agrima, Herr, Megan M.

Critical Care Medicine | July 5, 2021 | Volume: 50 | Issue: 1 | Pages: 81-92

10.1097/ccm.0000000000005149 | PMID 34259446 Get It

OBJECTIVES: To report the epidemiology, treatments, and outcomes of adult patients admitted to the ICU after cytokine release syndrome or immune effector cell-associated neurotoxicity syndrome. DESIGN: Retrospective cohort study SETTING: Nine centers across the U.S. part of the chimeric antigen receptor-ICU initiative. PATIENTS: Adult patients treated with chimeric antigen receptor T-cell therapy who required ICU admission between November 2017 and May 2019. INTERVENTIONS: Demographics, toxicities, specific interventions, and outcomes were collected. RESULTS: One-hundred five patients treated with axicabtagene ciloleucel required ICU admission for cytokine release syndrome or immune effector cell-associated neurotoxicity syndrome during the study period. At the time of ICU admission, the majority of patients had grade 3–4 toxicities (66.7%); 15.2% had grade 3–4 cytokine release syndrome and 64% grade 3–4 immune effector cell-associated neurotoxicity syndrome. During ICU stay, cytokine release syndrome was observed in 77.1% patients and immune effector cell-associated neurotoxicity syndrome in 84.8% of patients; 61.9% patients experienced both toxicities. Seventy-nine percent of patients developed greater than or equal to grade 3 toxicities during ICU stay, however, need for vasopressors (18.1%), mechanical ventilation (10.5%), and dialysis (2.9%) was uncommon. Immune Effector Cell-Associated Encephalopathy score less than 3 (69.7%), seizures (20.2%), status epilepticus (5.7%), motor deficits (12.4%), and cerebral edema (7.9%) were more prevalent. ICU mortality was 8.6%, with only three deaths related to cytokine release syndrome or immune effector cell-associated neurotoxicity syndrome. Median overall survival time was 10.4 months (95% CI, 6.64–not available mo). Toxicity grade or organ support had no impact on overall survival; higher cumulative corticosteroid doses were associated to decreased overall and progression-free survival. CONCLUSIONS: This is the first study to describe a multicenter cohort of patients requiring ICU admission with cytokine release syndrome or immune effector cell-associated neurotoxicity syndrome after chimeric antigen receptor T-cell therapy. Despite severe toxicities, organ support and in-hospital mortality were low in this patient population.
Abstract 2750: Multi-detector Computed Tomography Is An Accurate Screening Imaging Modality For Detection Of Thrombus In Patients Undergoing Catheter Ablation Of Atrial Fibrillation
Martinez, Matthew W. , Kirsch, Jacobo , Williamson, Eric E. , Cha, Yong‐Mei , Friedman, Paul A. , Ommen, Steve R. , Callahan, Mark J., Syed, Imran S., Feng, DaLi, Beinborn, Douglas S., Packer, Douglas L. , Brady, Peter A. , Asirvatham, Samuel J.

Circulation | July 3, 2021 | Volume: 116 | Issue: suppl_16 | Pages: No page available

10.1161/circ.116.suppl_16.ii_610-b Get It

Introduction Multi-detector computed tomography (MDCT) is commonly used to identify pulmonary vein and left atrial anatomy prior to catheter ablation for atrial fibrillation (CAAF). Additionally, transesophageal echocardiography (TEE) is utilized to exclude left atrial/left atrial appendage thrombus (ICT). Whether MDCT alone can be used to exclude thrombus obviating the need for TEE is unknown. Methods All Pts referred for CAAF at Mayo Clinic between March 2004 and October 2006 were included. Clinical data (including CHADS score), 64 slice MDCT (non-ECG gated), TEE and intra-cardiac echocardiograph (ICE) were all performed and recorded. Image data was reviewed independently and blinded. The left atrial appendage (LAA) was defined as fully opacified or underfilled. An underfilled LAA was further interrogated using a region of interest over the filling defect and mean attenuation in Hounsfield Units (HU) were recorded. Results In total 400 Pts (mean age 56 ± 10 yrs; 76% male; EF 56 ± 10 % ) were included. 362 had no ICT by TEE nor filling defect by MDCT. 38 patients had an underfilled LAA in whom ICT was confirmed by TEE in 7. Sensitivity and specificity of MDCT for ICT was 100% and 92% respectively with a NPV of 100%. In 19 Pts with underfilled LAA’s, a mean LAA emptying velocity was found to be significantly reduced at 26 cm/s (6 – 61 cm/s). Those with a thrombus had a mean attenuation value below 70 HU. CHADS2 score was higher (2.0 versus 1.0) in Pts with LAA filling defect versus those without LAA filling defect. All Pts with confirmed thrombus were taking Warfarin. ICT was not seen in any Pts aged <52 yrs with CHADS score ≤1. Conclusions Sensitivity and specificity of MDCT for detection of LAA thrombus is high. LAA filling defects on MDCT correlate with low emptying velocities by TEE and low attenuation value in HU. These data would suggest that in the absence of MDCT filling defect, no further imaging is required. TEE should be utilized prior to CAAF to investigate MDCT filling defects. Multidetector Computed Tomography for the Detection of LAA Thrombus
Abstract 5932: The Differences of Echocardiography and MRI Findings in Patients with Constrictive Pericarditis According to the History of Chest Radiation
Feng, DaLi, Glockner, James F., Martinez, Matthew W. , Edwards, William D. , Syed, Imran S., Araoz, Philip A. , Julsrud, Paul R., Bree, Jerome F, Williamson, Eric E. , Oh, Jae K. , Kim, Kye Hun

Circulation | July 3, 2021 | Volume: 118 | Issue: suppl_18 | Pages: No page available

10.1161/circ.118.suppl_18.s_1032-c Get It

Background: Radiation therapy (RT) to the chest may induce various combined cardiac problems such as constrictive pericarditis (CP), restrictive myocardial disease, and coronary artery disease. Therefore, it was hypothesized that the MRI and transthoracic echocardiographic (TTE) findings in patients with CP may differ according to the history of RT. Methods: A total of 68 patients with CP who performed both TTE and MRI study at Mayo Clinic from 2002 to 2008 were reviewed and divided into two groups according to the history of RT; RT group (group I, n=13, 53.6±9.8 years, 8 males) versus no RT group (group II, n=55, 59.0±14.8, 45 males). Results: The results of TTE study were summarized in table . Early diastolic velocity of septal mitral annulus (E′) and deceleration time (DT) of mitral inflow was significantly lower, and the ratio of early diastolic mitral inflow velocity (E) to E′ is significantly higher in group I than in group II. Left atrial volume index (LAVI) was significantly lower and LA area and left ventricular end-diastolic dimension (LVEDD) was significantly smaller in group I than in group II. Delayed enhancement of pericardium was the only significant finding in MRI and significantly prevalent in group I than in group II (100.0% in group I vs 63.6% in group II, p=0.012). The other MRI findings including pericardial thickness, left ventricular and right ventricular ejection fraction, and the presence of pericardial and pleural effusion were not different between the groups. Conclusion: In CP patients with the history of RT compared to patients without history of RT, E′ and DT was significantly lower, LAVI and LVEDD were smaller, pericardial DE in MRI was invariably found. The lower E′ velocity and decreased chamber size and volumes may be explained by RT induced coexisting myocardial disease. TTE findings of the patients
Abstract 5931: The Presence and Pattern of Late Gadolinium Enhancement on cardiac MRI in Amyloidosis is Associated with Other Markers of Prognosis
Syed, Imran , Glockner, James F., Araoz, Philip A. , Feng, DaLi, Martinez, Matthew W. , Oh, Jae K. , Grogan, Martha , Gertz, Morie A. , Dispenzieri, Angela

Circulation | July 3, 2021 | Volume: 118 | Issue: suppl_18 | Pages: No page available

10.1161/circ.118.suppl_18.s_1032-b Get It

Objective: Recent MRI studies have demonstrated the common occurrence of late gadolinium enhancement (LGE) in cardiac amyloidosis (CA). However, the association of LGE presence and pattern with other clinical, morphological, functional, and biochemical parameters has not yet been demonstrated. It is important to define this association, since many of these parameters (NYHA class, ventricular thickness, cardiac biomarkers) have prognostic implications. Methods: Of 151 patients with confirmed systemic amyloidosis who underwent LGE cardiac MRI between January 2006 and December 2007 to evaluate for possible CA, 120 (AL 100, senile 9, and familial 11) were included after meeting of inclusion and exclusion criteria. Cine MRI images were analyzed for morphologic and functional data. LGE images were analyzed for presence and pattern of LGE. Clinical data including ECG’s and cardiac biomarkers was obtained. Results: LGE evidence of CA was present in 95 patients and absent in 25 patients. Three main patterns of LGE were observed. These were global diffuse transmural (homogenous or heterogenous) or subendocardial, suboptimally nulled myocardium without clear hyperenhancement, and focal patchy LGE. Symptoms, morphologic/functional variables, ECG voltages, and cardiac biomarker levels were worst in patients with global diffuse LGE, followed by suboptimally nulled myocardium, focal patchy LGE, and absent LGE groups (Table 1 ). Conclusions: The presence of LGE in amyloidosis patients is associated with worse clinical, morphologic, functional, and biochemical parameters. Amongst patients with abnormal LGE, global diffuse (transmural or subendocardial) LGE is associated with the worst profile. This provides initial evidence that the presence and pattern of LGE in CA is associated with other markers of prognosis.
Abstract 5929: Evaluation of Myocardial Substrate with MRI Late Gadolinium Enhancement Allows for Earlier Detection of Cardiac Involvement Compared with Morphological Assessment in Primary AL Amyloidosis
Syed, Imran , Glockner, James F., Feng, DaLi, Araoz, Philip A. , Martinez, Matthew W. , Oh, Jae K. , Grogan, Martha , Gertz, Morie A. , Dispenzieri, Angela

Circulation | July 3, 2021 | Volume: 118 | Issue: suppl_18 | Pages: No page available

10.1161/circ.118.suppl_18.s_1032 Get It

Objective: In AL amyloidosis, early detection of cardiac involvement is desirable because of prognostic and therapeutic implications. Recent pilot MRI studies have demonstrated that late gadolinium enhancement (LGE) is a common finding in cardiac amyloidosis (CA) and reflects interstitial expansion due to amyloid infiltration. However it is not known whether evaluation of the myocardial substrate via LGE MRI may allow for earlier detection of CA compared with morphological assessment on the basis of increased left ventricular thickness (LVT). Methods: Between January 2006 and December 2007, 100 patients with confirmed AL amyloidosis underwent LGE MRI at our institution to evaluate for CA. Morphological evidence of CA was considered to be present when LVT was increased (mean of septum and inferolateral wall > 12 mm). LGE images were analyzed for presence and pattern of LGE. Clinical data was also reviewed. Results: Increased LVT was present in 69 patients. Abnormal LGE images were present in 76 patients (global diffuse transmural or subendocardial LGE in 43, suboptimally nulled myocardium in 18, and focal patchy LGE in 15 patients). LGE was present in 21 of 22 patients with a diagnosis of CA on cardiac biopsy. Seven patients (10%) with increased LVT did not have LGE. Conversely of 31 pts with normal LVT, 14 (45%) had abnormal LGE on MRI (usually suboptimally nulled myocardium or focal patchy LGE) and also had significantly higher incidence of low voltage ECG (50% vs. 0%), lower absolute limb lead voltage (6.5±3 vs. 9.7±2.6 mm), increased RV thickness (4.9±1.1 vs. 4.1±1) and higher BNP (316±376 vs. 107±103) compared to 17 patients without LGE (Table 1 ). Conclusions: MRI LGE is common in patients with CA and evaluation of the myocardial substrate using this technique may allow for earlier detection of cardiac involvement in AL amyloidosis compared with morphological assessment on the basis of increased LVT.
Abstract CT026: A phase II trial of neratinib (NER) or NER plus fulvestrant (FUL) (N+F) in HER2 mutant, non-amplified (HER2mut) metastatic breast cancer (MBC): Part II of MutHER
Cynthia, X. , Nangia, Julie R. , Lu, Janice , Valdez-Albini, Frances, Jones, Jason M. , Thomas, Shana , Anderson, J. L. , Haas, Brittney , Hamann, Kimberly M., Bryce, Richard , Lalani, Alshad S. , Kimmick, Gretchen , Pegram, Mark D. , Bose, Ron , Luo, Jingqin , Freedman, Rachel A. , Pluard, Timothy , Cobleigh, Melody , Lin, Nancy U. , Winer, Eric P. , Marcom, Paul Kelly , Anderson, Jill, Carey, Lisa A. , Goetz, Matthew P. , Gao, Feng , Ellis, Matthew J.

Cancer Research | July 1, 2021 | Volume: 81 | Issue: 13_Supplement | Pages: CT026-CT026

10.1158/1538-7445.am2021-ct026 Get It

Abstract Introduction: The irreversible pan-HER inhibitor NER showed modest single agent activity for HER2mut MBC in Part I of MutHER trial. In Part II, we hypothesized that (1) N+F would improve activity in estrogen receptor positive (ER+) HER2mut MBC due to ER-HER2 crosstalk and (2) dual HER2 blockade by adding trastuzumab at disease progression (PD) could overcome resistance. Methods: Pts with ER+HER2mut MBC were enrolled to 2 cohorts (FUL treated or naive) to receive N+F with diarrhea prophylaxis. ER- pts received NER in an exploratory ER- cohort. Trastuzumab was added at PD if approved by insurance. Simon's Minimax 2-stage phase II design with the primary endpoint of clinical benefit rate (CBR: rates of complete/partial response [CR/PR] plus stable disease [SD] &gt;24 weeks [wks]), with anticipated vs null hypothesis being CBR of 55% vs 35% (FUL treated) or 65% vs 40% (FUL naïve) with 80% power, 1 sided 0.05 alpha, was used. Secondary endpoints included progression free survival (PFS) and adverse events (AEs). Serial blood samples were analyzed for circulating tumor DNA (ctDNA) by Guardant360 for concomitant mutations, HER2mut variant allele frequency (VAF) dynamics, and resistance mechanisms. Results: Between Sep. 2015 and Oct. 2020, 40 pts with HER2mut MBC were enrolled, completing the 1st stage of each ER+ cohort. 35 pts (21 FUL treated, 10 FUL naïve, 4 ER-) were evaluable for response, with median age 63 (35-82) years, 3 (0-12) prior MBC regimen, lobular BC in 13 (37%) and visceral mets in 32 (91%) pts. 21 (68%) ER+ pts had prior CDK4/6 inhibitor. All but 1 pt has come off study due to PD. Table 1 shows the efficacy by cohort. Further enrollment is closed per protocol. Adding trastuzumab at PD induced CB in 4 (3 PR, 1 SD≥24 wks) of 5 pts (1 ER-, 4 ER+), with PFS 28 (95% CI 18~NA) wks. Common AEs across cohorts were diarrhea (G3 21%) and fatigue (G3 5%). No G4 AEs. ctDNA HER2mut was detected in 72% (23/32) baseline (BL) samples tested. In pts with paired samples, HER2mut VAF decreased at C1D15/C2D1 from BL in 75% (15/20) and rose in 89% (16/18) at PD. Acquired HER2mut, including the T798I gatekeeper mutation, were detected in 2 pts at PD. Mutations in TP53 (53%), PIK3CA (43%), and CDH1 (35%) were common, but none significantly associated with PFS in all or ER+ pts. Conclusions: NER, or N+F, is active for HER2mut MBC with good tolerability. Adding trastuzumab at PD induced further response, supporting dual HER2 blockade for HER2mut MBC. Table 1.EfficacyCohortFUL treatedFUL naïveER-Best Response, n evaluablen = 21n = 10n = 4CR, n100PR, n431SD (≥ 24 wks), n300SD (&lt; 24 wks), n1030PD, n343CBR, n with CB/total n evaluable, % (95% CI)8 of 20*, 40% (19~64%)3 of 10, 30% (7~65%)1 of 4, 25% (0.6~81%)mPFS (95% CI), wks, ITT (n)24 (16~31) wks, (n = 24)20 (8~NA) wks, (n = 11)8.5 (8~NA) wks, (n = 5)*20 of 21 pts are evaluable for CBR in the FUL treated Cohort as 1 pt had SD as best response and treatment is still ongoing. ITT (intent to treat) population is used for mPFS estimate. Citation Format: Cynthia X. Ma, Jingqin Luo, Rachel A. Freedman, Timothy Pluard, Julie Nangia, Janice Lu, Frances Valdez-Albini, Melody Cobleigh, Jason Jones, Nancy U. Lin, Eric Winer, P. Kelly Marcom, Shana Thomas, Jill Anderson, Brittney Haas, Kimberly M. Hamann, Richard Bryce, Alshad S. Lalani, Lisa Carey, Matthew Goetz, Feng Gao, Gretchen Kimmick, Mark Pegram, Matthew J. Ellis, Ron Bose. A phase II trial of neratinib (NER) or NER plus fulvestrant (FUL) (N+F) in HER2 mutant, non-amplified (HER2mut) metastatic breast cancer (MBC): Part II of MutHER [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr CT026.