Citations

Abstract Background: The COVID-19 pandemic rapidly altered health care worldwide. To save protective equipment and minimize exposures, many hospitals stopped some or all cancer surgery, leading oncologic providers to quickly adjust patient management. The goal of this study is to describe the breast cancer patient level changes which occurred during the initial months of COVID-19 in the United States. Methods: The American Society of Breast Surgeons developed a COVID-19 specific registry, within the established HIPPA compliant Mastery of Breast Surgery Program. Surgeons entered patient demographic data as well as their surgical and medical care (Neoadjuvant endocrine (NET) vs Neoadjuvant chemotherapy (NCT)). Data fields tracked whether decisions were usual for that practice, or modified due to COVID-19. Results: Between 3/1 and 6/17/2020, data from 1781 patients was entered by 154 surgeons. Mean age was 63, 78% Caucasian, 10% African American, 6% Hispanic; with geographic distribution ranging from 10.8% Northwest to 29.5% Northeast. Initial consultation took place in-person for 94.8% and only 5.2% (89) occurred via video/telephone. To date, just over 1% (14) of patients tested positive for COVID-19. Mean invasive tumor size was 21.2mm and 15.7% were node positive. Of 1445 invasive breast cancers 75% (1081) were ER +/HER2-, 13.5% (195) HER2+, 11.1% (160) triple negative (TNBC) (9/missing data). DCIS comprised 18.2% (325) of the cohort. Of 267 cases of ER+ DCIS, 49% (131) had primary surgery and 49% (130) received NET. The majority of NET use was due to COVID-19, 95% (124). Almost all (50/52) ER- DCIS underwent primary surgery (6/missing ER). Table 1 describes the management for the 1436 patients with invasive cancer with known biomarkers. NET due to COVID-19 was utilized in 45% (482), with only 5% (54) as part of usual practice. Increasing age was not a statistically significant factor in the use of NET (OR 0.99, 95% CI 0.97-1.01). In comparison to patients from the Northwest, patients from the Southwest and Northeast had the greatest use of NET(COVID-19) vs NET(usual) (ORs 14.4 and 4.6) Genomic assay testing was performed on the core biopsy in 216 patients, with 65% (141) due to COVID-19. Among the patients who had genomic testing due to COVID-19, 116 (82%) had NET, 18 (13%) had NCT, with the remaining having primary surgery. Of 472 patients treated with primary surgery for which the impact of COVID-19 was provided, surgery was delayed in 20% (96). Patients from the Northeast had a 2.1 x greater odds of having surgery delayed in comparison to those from the Midwest. Patients also experienced changes to their surgical plan with the most common changes being 6% (27) converting from mastectomy to breast conservation and 7% (34) from mastectomy with reconstruction to mastectomy without reconstruction. Conclusion: COVID-19 led to significant modifications in breast cancer treatment, including high rates of NET, genomic assay testing on core biopsies as well as delays in surgery; each of which were consistent with the prioritization and treatment recommendations from the COVID-19 Pandemic Breast Cancer Consortium. The majority of patients with TNBC and HER2+ disease received guideline concordant NCT. The ASBrS Mastery COVID-19 registry provides a snapshot into the rapid care changes caused by the pandemic, has ongoing data entry and analysis and will enable understanding of the impact on long term breast cancer outcomes. Table 1: Biomarker specific treatmentsER+/HER2- (1081)TNBC (160)HER2+/any ER (195)Mean Age656159African American (%)97(9%)21(13%)27(14%)Primary Surgery (usual)386 (36%)50 (31%)37 (19%)Primary Surgery (COVID-19)28 (2.6%)6 (3.7%)6 (3.1%)NET (usual)54 (5%)NA1(0.5%)NET (COVID-19)482 (45%)NA6 (3.6%)NCT (usual)90 (8.3%)98 (61%)137 (70%)NCT (COVID-19)39 (3.6%)6 (3.7%)8 (4.1%) Citation Format: Lee Gravatt Wilke, Toan T Nguyen, Qiuyu Yang, Bret M Hanlon, Kathryn A Wagner, Pamela Strickland, Eric A Brown, Jill Dietz, Judy C Boughey. Impact of the COVID-19 pandemic on the multidisciplinary management of breast cancer: Initial analysis of the american society of breast surgeons mastery COVID-19 registry [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr SS2-01.

Abstract Background: Androgen receptor (AR) is expressed in 60%-90% of breast cancers. The role of AR in breast cancer largely depends on estrogen receptor (ER) status and remains controversial. In ER+ cancers, AR expression is associated with improved prognosis. Enzalutamide (ENZ), an AR antagonist, impairs AR signaling, inhibits ER+/AR+ breast cancer cell proliferation and has been shown to mitigate resistance to anti-estrogen therapies. A recent study identified that RAD140, an AR agonist, suppressed the growth of ER+/AR+ breast cancer via stimulating AR signaling, resulting in down regulation of ERα. Both AR agonists and antagonists are effective in treating ER+ breast cancers. Identifying the subgroup of patients who most likely will benefit from an individual drug is important in clinical practice. Here, we sought to characterize the relative AR to ER levels and their relationships to drug response in ER+ breast cancers.Methods: We evaluated AR and ER expression levels among 68 samples with ER+ breast cancers. On each tumor, IHC staining for AR and ER were performed and results were scored by multiplying the percentage of positive cells by the intensity. TCGA-RPPA (reverse phase protein array) dataset was used to verify AR protein distribution in ER+ cancers. We created MCF7 and T47D cells with doxycycline-inducible AR and ER expression system to manipulate the relative AR to ER ratios and determined the antitumor activity of ENZ and RAD140 by cell proliferation assays. The levels of AR and ER in cells were measured by western blot. Linear regression was used to test the association between dose-response area under curve (AUC) and AR, ER levels. Drug preference was modeled against AR/ER expression levels (AR/ER ratios) using logistic regression.Results: Among 68 ER+ breast cancers, 69.12% were AR-positive. More than 2/3 cases (48 of 68) had more ER than AR expressed. The AR to ER ratios varied from 0 to 6. In the TCGA cohort, 84.15% of 347 ER+ patients had AR/ER ratios less than 1.The range of AR to ER ratios in TCGA dataset were comparable with our data (0.004 to 4.210). In our cell line models, the AR/ER ratios were controlled between 0.19 to 4.05. We found that the AUC of RAD140 was negatively associated with AR protein levels (P=0.008) and AR/ER ratios (P=0.013), and not significantly associated with ER expression levels. On the other hand, the AUC of ENZ was significantly negatively associated with ER protein (P=0.0016) but postiviely associated with AR/ER ratio (p=0.037). Preferred treatment comparing efficacy of the two drug can be best determined at extremes of AR/ER ratios. Using clinically relevant dosages, our model predicted that ENZ (10µM) would be a preferred treatment choice and have a better treatment efficacy compared with RAD140 when the AR/ER ratio was ≤ 0.42, whereas RAD140 (1µM) would be the preferred choice with a better treatment efficacy compared with ENZ when AR/ER ratios were ≥ 3.1 The efficacy preference of the two drugs are equivocal for AR/ER ratios between 0.42 and 3.10. Conclusion: We developed preclinical models using AR and ER expression levels to predict AR-targeting drug response. The results support the use of RAD140 in AR high patients and those with an AR/ER ratio >3.10, and enzalutamide in AR low patients and those with an AR/ER ratio <0.42. Equipoise on choice of drug was found for AR/ER ratios of 0.42-3.10. RAD140 and enzalutamide are compelling candidates for monotherapy or combination with anti-estrogen therapies in ER+/AR+ breast cancer. Future clinical validation of the models and therapeutic effect is warranted. Citation Format: Lixuan Wei, Huanyao Gao, Jia Yu, Duan Liu, Huan Zhang, Thanh Nguyen, Marie R Passow, Jodi M Carter, Richard M Weinshilboum, James N Ingle, Liewei Wang. Computational modeling of androgen receptor (AR) and estrogen receptor as predictive biomarkers of response to AR agonists and antagonists [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS5-36.

More and more breast cancer patients are turning to autologous options for reconstruction. Deep Inferior Epigastric Perforator (DIEP) flap reconstruction is considered the gold standard flap breast reconstruction procedure; however, it requires a significant number of resources, including two surgeons and microsurgical equipment. A multidisciplinary group was tasked with reducing operative time of DIEP flap procedures by 25% so that complex surgeries can become more routine and accessible to patients. Using participatory ergonomics, members of the operative team were engaged to identify interventions. Following implementation, 22 DIEP flap cases were evaluated using workload surveys and patient outcomes to determine the success of the interventions. DIEP flap surgical durations were reduced by 25% on average (M=12.9 hours, SD=5.7 to M=9.7 hours, SD=1.4). When cases lasted longer than 9 hours, surgeons reported 31% more physical demand and 78% more fatigue than cases that were 9 hours or less. Survey results linked positive team characteristics to reduced frustrations and distractions.

Deep inferior epigastric perforator (DIEP) flap is a surgical procedure using tissue harvested from the abdominal area to reconstruct the breast after a mastectomy. Primary surgical phases include the abdominal flap harvest, chest dissection, and anastomosis. In this study, inertial measurement units (IMUs) were used to measure surgeon upper body postures while performing DIEP flap procedures. Ergonomic risks of musculoskeletal disorders were evaluated using the Rapid Upper Limb Assessment (RULA) based on the postures obtained from the IMUs. Joint angles were analyzed using a one-way ANOVA. The neck and back had higher joint angles during the abdominal flap (M=32°, 17°, respectively) and chest dissection (M=31°, 18°, respectively) phases than the anastomosis phase. These high-risk postures may lead to musculoskeletal disorders. Future interventions should focus on improving the postures of the neck and back during the abdominal flap and chest dissection phases of the procedure.

Background: Clonal cytopenias of Undetermined Significance (CCUS) have a higher risk of progression to myeloid neoplasm (MN) compared to idiopathic cytopenias of undetermined significance (ICUS) (Malcovati et al., Blood, 2017). The implementation of flow cytometric (FC) immune-phenotyping and next generation sequencing (NGS) in clinical practice has improved the diagnosis of these entities but the clinical significance and interaction of these abnormal results are still unknown. In this study we investigated predictive factors that play role in survival and progression to MN in patients with ICUS/CCUS. Methods: Patients (Pts) who had undergone evaluation for unexplained cytopenia and had undergone FC and bone marrow morphological assessment between 3/2015-3/2020 at Mayo Clinic Rochester were included. Pts were excluded if a malignant hematological disorder was diagnosed prior to the time of FC. FC included evaluation of the following parameters: Abnormal expression of HLA-DR/CD13, CD2, CD7, CD45, and CD56 on blasts; and abnormal CD13/CD16 expression and side scatter on granulocytic cells. NGS panel up to 2018 included 34 genes, ASXL1, BCOR, BRAF, CALR, CBL, CEBPA, CSF3R, DNMT3A, ETV6, EZH2, FLT3, GATA1, GATA2, IDH1, IDH2, JAK2, KIT, KRAS, MPL, MYD88, NOTCH1, NPM1, NRAS, PHF6, PTPN11, RUNX1, SETBP1, SF3B1, TERT, TET2, TP53, U2AF1, WT1, and ZRSR2; in 2018, BRAF was omitted and 12 genes were added, ANRD26, DDX41, ELANE, ETNK1, KDM6A, MYD88, NOTCH1, RAD21, SH2B3, SRP72, SMC3, and STAG2. Results: Characteristics: Of 490 consecutive pts, 238 (median age 69 years (range 19-92), 66% males) met our inclusion criteria as ICUS. 86 (36%) pts had CCUS (abnormal cytogenetics and/or tested positive for pathogenic mutations on NGS). After a median follow-up of 28 months (95% CI: 20 to 31 months), 21 (25%) patients developed MN and 23 (27%) died during follow-up. Comparing ICUS vs CCUS: upon comparing CCUS pts to ICUS, several factors were found to be significantly different: CCUS pts were older (p= .02); majority male (p= .04), had more abnormal HLA-DR/CD13 (p <.0001), more side-scattered light by FC (p <.0001), more pancytopenia on follow up (p= .02) and more morphologic atypia (<.0001). Overall survival (OS) outcomes in CCUS: Several covariates were significant in univariate models, and model selection was used to generate a risk score based on abnormal CD7, abnormal CD13/CD16, abnormal HLA-DR/CD13, splenomegaly and history of prior chemotherapy or radiotherapy (range: 0 - 4; HR=2.58, [95 CI: 1.69 - 3.94], p<.0001). Risk scores were grouped as low risk (score=0), intermediate risk (score=1), and high risk (score=2+), with estimated 2-yr-OS of 95%, 84%, 40%, respectively (Figure 1). An extended risk score model including NGS factors added ASXL1 and IDH1 mutation status to the previous model (range: 0 - 6; HR=2.72, [95 CI 1.82 - 4.06], p<0.0001). MN-free survival (MNFS) in CCUS: 37 pts either progressed to MN and/or died with a median follow up time for MNFS of 22.4 months. Similar for OS, model selection approaches yielded a composite risk score: splenomegaly, BCOR mutation status, mutation in RAS signaling pathway, abnormal expression of flow markers CD13/CD16, HLA-DR/CD13 or CD7 (HR=3.23, [95 CI: 1.90 - 5.49], p=<0.0001). Risk scores were grouped as low risk (score=0), intermediate risk (score=1), and high risk (score ≥ 2), with estimated 1-yr MNFS of 84%, 74%, and 31%, respectively (Figure 2). Conclusion: CCUS has unique features compared to ICUS. Several factors, including clinical characteristics, immune-phenotyping by FC, and somatic mutations have important impact on risk of progression to MN and on overall survival. Our findings serve as proof-of-concept that such integrated models could help identify CCUS patients at higher risks for progression to MN or death. They can guide treatment accordingly and should be evaluated further. Disclosures Shah: Dren Bio: Consultancy.

Introduction: IBER is an oral, potent novel cereblon E3 ligase modulator (CELMoD) agent with marked synergistic tumoricidal and immune-stimulatory effects in combination with BORT or DARA in preclinical models. CC-220-MM-001 is a phase 1/2 study evaluating dose escalations of IBER with different treatment combinations in independent cohorts, in patients (pts) with RRMM (NCT02773030); the IBER + DEX cohort showed a favorable safety profile with promising efficacy and a selected IBER RP2D of 1.6 mg 21/28 days (D). Here, we present results from the IBER + DARA + DEX (IberDd) and IBER + BORT + DEX (IberVd) cohorts. Methods: Eligible pts had received ≥ 2 prior regimens in the IberDd cohort, and ≥ 1 prior regimen in the IberVd cohort, containing at least lenalidomide or pomalidomide, and a proteasome inhibitor (PI), and had experienced disease progression on or within 60 days of last MM therapy. Escalating doses of IBER were given orally, in the IberDd cohort on D1-21, with DARA (16 mg/kg) on D1, D8, D15, and D22 (cycles [C]1-2), D1 and D15 (C3-6), and D1 (C ≥ 7), of each 28-day cycle; in the IberVd cohort, on D1-14, with BORT (1.3 mg/m2) on D1, D4, D8, and D11 (C1-8), and on D1 and D8 (C ≥ 9), of each 21-day cycle. In both cohorts DEX was given weekly. Primary objectives were to evaluate MTD, RP2D, and safety separately for each cohort; a key secondary objective was preliminary assessment of efficacy. Immune profiling was evaluated by flow cytometry from pt peripheral blood at C1D1, C2D15, C4D1, and C4D15. Results: As of June 18, 2020, 19 pts had received IberDd and 21 pts IberVd. Baseline characteristics for the 2 independent cohorts are shown in the table. All pts were refractory to their last prior regimen, and exposure to prior regimens was heterogeneous. IBER doses ranged from 1.0 to 1.6 mg; the MTD/RP2D has not been reached in either cohort. Median follow-up was 5 (0-14) and 3 (0-11) months, 10 (53%) and 13 (62%) pts continue on treatment, median cycles received was 5 (1-14) and 4.5 (1-17), with IberDd and IberVd, respectively. Grade (Gr) 3-4 treatment-emergent adverse events (TEAEs) were reported in 14 (78%) pts with IberDd, and in 13 (65%) pts with IberVd. Most frequent Gr 3-4 TEAEs of interest included neutropenia (50%), leukopenia (22%), and anemia (22%) with IberDd; and neutropenia (20%) and thrombocytopenia (20%) with IberVd. In both cohorts, neutropenia was managed with G-CSF. One pt (IberDd; 1.2 mg dose) had Gr 4 neutropenic sepsis. Occurrence of Gr 3-4 non-hematological TEAEs was low in both cohorts. One pt had Gr 2 infusion-related reaction with IberDd, and 3 pts had Gr 1-2 peripheral neuropathy with IberVd. Six (33%) and 4 (20%) pts had IBER dose reductions with IberDd and IberVd, respectively. In the IberDd cohort, with 12/19 (63%) DARA-refractory pts and 11 (58%) quad-class-refractory pts, the overall response rate (ORR) was 35% across all dosing groups (2 very good partial responses [VGPRs], 4 partial responses [PRs]); the clinical benefit rate (CBR) was 47% and disease control rate (DCR) was 88%. In the IberVd cohort, with 16/21 (76%) PI-refractory pts, 9 (43%) BORT-refractory pts, and 10 (48%) quad-class refractory pts, ORR was 50% (1 complete response, 3 VGPRs, 6 PRs); CBR was 65% and DCR was 85%. Responses with IberDd and IberVd were observed irrespective of DARA- and BORT-refractoriness, respectively. Median time to response was 4.1 (4.1-12.0) and 4.9 (3.0-13.1) weeks, in the IberDd and IberVd cohorts, respectively; median duration of response was not reached in both cohorts. Immune profiling showed dose-dependent decreases in B cells and increases in activated and differentiated T cells, in both cohorts. Except for reductions in CD38+ T cells in pts receiving IberDd, these observations were similar in pts treated with IBER + DEX. Conclusions: IberDd and IberVd showed a favorable tolerability profile in heavily pretreated RRMM pts, with promising clinical activity, even among pts refractory to the last prior regimen and previously exposed to IMiD agents, PIs, and CD38 antibodies. Immune-profiling data confirm that IBER + DEX was pharmacodynamically active in triplet combination and not augmented by the addition of DARA or BORT. The study is ongoing with continued enrollment at the 1.6 mg dose level for both cohorts. Updated results, including the MTD/RP2D, will be presented at the meeting. These results support the further development of IBER-based regimens in MM; phase 3 trials are planned to further evaluate these combinations. Disclosures van de Donk: Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding; Bayer: Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees; Ferrer: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees, Research Funding. Popat:Takeda: Consultancy, Honoraria, Other: Travel support, Research Funding; Bristol Myers Squibb: Consultancy, Honoraria; Celgene: Consultancy, Honoraria; Janssen: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company); AbbVie: Consultancy, Honoraria; GSK: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company). Larsen:Janssen Oncology: Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees. Minnema:Servier: Consultancy; Kite, a Gilead Company: Speakers Bureau; Celgene: Other: travel support, Research Funding; Amgen: Consultancy. Jagannath:BMS, Janssen, Karyopharm, Legend Biotech, Sanofi, Takeda: Consultancy. Oriol:Sanofi: Membership on an entity's Board of Directors or advisory committees; GlaxoSmithKline: Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy; Bristol-Myers Squibb: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Amgen: Consultancy, Speakers Bureau. Zonder:Prothena: Consultancy; Intellia: Membership on an entity's Board of Directors or advisory committees, Other: Personal fees; Celgene: Research Funding; BMS: Consultancy, Research Funding; Amgen: Membership on an entity's Board of Directors or advisory committees, Other: Personal fees; Oncopeptide: Membership on an entity's Board of Directors or advisory committees, Other: Personal fees; Alnylam: Membership on an entity's Board of Directors or advisory committees, Other: Personal fees; Janssen: Consultancy, Other: Personal fees; Caelum: Consultancy; Takeda: Membership on an entity's Board of Directors or advisory committees, Other: Personal fees. Richardson:Celgene/BMS, Oncopeptides, Takeda, Karyopharm: Research Funding. Rodriguez-Otero:Sanofi: Consultancy, Honoraria; Medscape: Membership on an entity's Board of Directors or advisory committees; Celgene/Bristol-Myers Squibb: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company); GlaxoSmithKline: Consultancy, Current Employment, Current equity holder in publicly-traded company, Honoraria; Abbvie: Consultancy, Honoraria; Kite: Consultancy, Honoraria; Janssen: Consultancy, Honoraria, Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company); Amgen: Consultancy, Honoraria; Oncopeptides: Consultancy, Honoraria. Badros:Amgen: Consultancy; University of Maryland: Current Employment. Stadtmauer:Sanofi: Consultancy; AbbVie: Research Funding; Takeda: Consultancy; Bristol Myers Squibb: Consultancy, Research Funding. Bringhen:Bristol-Myers Squibb: Honoraria; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Karyopharm: Membership on an entity's Board of Directors or advisory committees; Takeda: Consultancy; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees. Siegel:Takeda: Consultancy, Honoraria, Speakers Bureau; BMS: Consultancy, Honoraria, Speakers Bureau; Amgen: Consultancy, Honoraria, Speakers Bureau; Merck: Consultancy, Honoraria, Speakers Bureau; Janssen: Consultancy, Honoraria, Speakers Bureau; Celulatiry: Consultancy; Karyopharma: Consultancy, Honoraria. Gamberi:Janssen: Consultancy, Honoraria; GSK: Consultancy; Amgen: Consultancy, Honoraria; Sanofi: Consultancy, Honoraria; Bristol Myers Squibb: Consultancy, Honoraria. Gironella Mesa:Janssen: Consultancy, Honoraria; Bristol Myers Squibb: Honoraria, Speakers Bureau. Sonneveld:Bristol-Myers Squibb: Consultancy, Honoraria, Research Funding; Amgen: Consultancy, Honoraria, Research Funding; Janssen: Consultancy, Honoraria, Research Funding; Karyopharm: Consultancy, Honoraria, Research Funding; Skyline Dx: Honoraria, Research Funding; Takeda: Consultancy, Honoraria, Research Funding; Sanofi: Consultancy. Nguyen:Bristol Myers Squibb: Current Employment, Current equity holder in publicly-traded company. Di Micco:Bristol Myers Squibb: Current Employment, Current equity holder in publicly-traded company. Sorrell:Children's Oncology Group: Other: Non-member; Previous Study Chair AAML08B1; Bristol Myers Squibb: Current Employment. Chen:Bristol Myers Squibb: Current Employment, Current equity holder in publicly-traded company. Amatangelo:Bristol Myers Squibb: Current Employment, Current equity holder in publicly-traded company. Kueenburg:Celgene International Sàrl, a Bristol Myers Squibb Company, Boudry, Switzerland: Current Employment. Lonial:Onyx: Honoraria; Novartis: Consultancy, Honoraria, Other: Personal fees; Genentech: Consultancy; Amgen: Consultancy, Honoraria, Other: Personal fees; Merck: Consultancy, Honoraria, Other: Personal fees; Abbvie: Consultancy; Millennium: Consultancy, Honoraria; Karyopharm: Consultancy; Sanofi: Consultancy; JUNO Therapeutics: Consultancy; TG Therapeutics: Membership on an entity's Board of Directors or advisory committees; Takeda: Consultancy, Other: Personal fees, Research Funding; Janssen: Consultancy, Honoraria, Other: Personal fees, Research Funding; BMS: Consultancy, Honoraria, Other: Personal fees, Research Funding; GSK: Consultancy, Honoraria, Other: Personal fees.

Cancer is caused primarily by genomic alterations resulting in deregulation of gene regulatory circuits in key growth, apoptosis, or DNA repair pathways. Multiple genes associated with the initiation and development of tumors are also regulated at the level of mRNA decay, through the recruitment of RNA-binding proteins to AU-rich elements (AREs) located in their 3′-untranslated regions. One of these ARE-binding proteins, tristetraprolin (TTP; encoded by Zfp36 ), is consistently dysregulated in many human malignancies. Herein, using regulated overexpression or conditional ablation in the context of cutaneous chemical carcinogenesis, we show that TTP represents a critical regulator of skin tumorigenesis. We provide evidence that TTP controlled both tumor-associated inflammation and key oncogenic pathways in neoplastic epidermal cells. We identify Areg as a direct target of TTP in keratinocytes and show that EGFR signaling potentially contributed to exacerbated tumor formation. Finally, single-cell RNA-Seq analysis indicated that ZFP36 was downregulated in human malignant keratinocytes. We conclude that TTP expression by epidermal cells played a major role in the control of skin tumorigenesis.