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Lesser, Glenn J.

https://orcid.org/0009-0003-5471-8907

Mayo Clinic

University of Minnesota

Citations 21

Evaluation of Regorafenib in Newly Diagnosed and Recurrent Glioblastoma: GBM AGILE Phase II/III Bayesian Randomized Platform Trial
Wen, Patrick Y. , Berry, Donald A. , Buxton, Meredith , Colman, Howard , Groot, John de , Lim, Michael, Mellinghoff, Ingo K. , Perry, James, Weller, M, Blondin, Nicholas A., Butt, Omar H. , Damek, Denise M., Fuente, Macarena I. de la , Drappatz, Jan, Dunbar, Erin, Giglio, Pierre , Hyddmark, Emma Viktoria, Iwamoto, Fabio, Jaeckle, Kurt A. , Kim, Lyndon, Kling, Heather M., Lee, Eudocia Q., Mantica, Megan , Mikkelsen, Tom, Newton, Herbert B. , Walbert, Tobias , Weathers, Shiao‐Pei , Lassman, Andrew B. , Group, for the GBM AGILE Regorafenib Study, Alexander, Brian, Anker, Lars , Berry, Nicholas , Cloughesy, Tim, Connelly, Jennifer , Detry, Michelle A. , Fitzgerald, Mark, Gordon, Gary, Graves, Todd, Hu, Jethro , Hyddmark, Emma Maria Viktoria, Johnson, Adam, Kalabic, Marija, Lesser, Glenn J., Marion, Joe , Owen, Scott, Perry, James R, Peters, Katherine B., Powell, Ashley, Saunders, Christina T., Tanner, Kirk, Untch, Sarah, Wilcox, Emma, Yung, W. K. Alfred, Lim, Michael , Buxton, Meredith , de Groot, John , Mellinghoff, Ingo K , Weller, Michael , De La Fuente, Macarena , Lee, Eudocia Q , Mantica, Megan , Nabors, Louis Burt , Newton, Herbert B , Olson, Jeffrey J. , Schiff, David , Walbert, Tobias , Weathers, Shiao-Pei , Cloughesy, Timothy F , Lassman, Andrew B , Berry, Donald , Colman, Howard , Blondin, Nicolas, Drappatz, Jan , Iwamoto, Fabio M., Lee, Eudocia Q. , Mikkelsen, Tom , Nabors, Burt , Newton, Herbert B. , Cloughesy, Timothy F. , Anderson, Mark D., Cavenee, Webster K. , Connelly, Jennifer , Ellingson, Benjamin M. , Galanis, Evanthia , Gordon, Gary, Graber, Jerome J. , Khasraw, Mustafa , Lesser, Glenn J. , McGlothlin, Anna , Peters, Katherine B. , Saunders, Christina T. , Sulman, Erik P. , Tanner, Kirk, Yung, W.K. Alfred

Journal of Clinical Oncology | April 14, 2026 | Volume: 44 | Issue: 18 | Pages: 1676-1686

10.1200/jco-25-01137 Get It

PURPOSE GBM AGILE (ClinicalTrials.gov identifier: NCT03970447 ) is a phase II/III Bayesian adaptive platform registration trial testing multiple arms against a common control; the primary end point is overall survival (OS). Regorafenib, a multikinase inhibitor, showed OS benefit in recurrent (RD) glioblastoma in the phase II REGOMA trial and entered GBM AGILE as the first investigational arm. METHODS Patient subtypes included in the regorafenib arm of GBM AGILE were newly diagnosed unmethylated (NDU) and RD glioblastoma. Prospective defined sets of subtypes, or arm signatures, were NDU, RD, and all (NDU + RD). As the first investigational arm in GBM AGILE, regorafenib was equally randomized to the control arm. Treatment in the control arm is temozolomide + radiotherapy (in newly diagnosed) or lomustine (in RD). Efficacy was assessed by OS hazard ratio (HR), arm/control, and demonstrated when the Bayesian probability of benefit (HR <1.00) was ≥98%. Analysis was performed monthly for limited efficacy, which occurs when the Bayesian predictive power is <25% for all signatures, and determines stopping enrollment. Follow-up continued for 12 months after accrual stopped. RESULTS When the predictive power was <25% in all predefined signatures for regorafenib, accrual stopped for limited efficacy. The final analysis did not demonstrate OS improvement in the regorafenib arm in RD nor NDU glioblastoma. Median HRs were 1.05 (NDU), 1.07 (RD), and 1.07 (all) with final probabilities of benefit (HR <1.00) of 0.421 (NDU), 0.312 (RD), and 0.296 (all). Regorafenib was associated with increased toxicity relative to control. CONCLUSION GBM AGILE did not show superiority of regorafenib over control in RD (lomustine) or NDU (temozolomide + radiotherapy) glioblastoma, yet caused increased toxicities. Regorafenib has been removed from National Comprehensive Cancer Network guidelines as a treatment option for RD.
Evaluating “brain permeability”: A critical issue for the development of therapeutic agents for primary and metastatic brain tumors
Grossman, Stuart A. , Barone, Amy , Strowd, Roy E, Rais, Rana , Duke, Elizabeth , Wearne, Emily , Price, Lauren , Hendrix, C. W., Schreck, Karisa C. , Lesser, Glenn J. , Sanai, Nader , Blakeley, Jaishri O, Nabors, Burt L., Sarkaria, Jann N, Peereboom, David, Schiff, D., Prowell, Tatiana M. , Elmquist, William F. , Hendrix, Craig W. , Strowd, Roy E. , Strowd, Roy E , Price, Lauren S L , Hendrix, Craig , Lesser, Glenn , Romo, Carlos , Portnow, Jana , Blakeley, Jaishri O , Kamson, David O , Nabors, Louis Burt , Searson, Peter C , Sarkaria, Jann N , Peereboom, David M , Schiff, David , Prowell, Tatiana M , Grossman, Stuart A , Romo, Carlos G. , Blakeley, Jaishri O. , Kamson, David , Nabors, Burt , Sarkaria, Jann N. , Peereboom, David M.

Neuro-Oncology | March 7, 2026 | Volume: 28 | Issue: 7 | Pages: 1599-1611

10.1093/neuonc/noag051 Get It

Abstract Current assessments of brain permeability rely predominantly on drug delivery to contrast-enhancing tumor regions. However, substantial portions of central nervous system (CNS) tumors reside within non-enhancing brain (NEB), where drug concentrations frequently remain subtherapeutic. This collaborative Adult Brain Tumor Consortium and Food and Drug Administration workshop aimed to identify criteria for defining NEB permeability to accomplish 2 critical objectives: (1) allocate clinical trial resources toward agents achieving therapeutic NEB concentrations and (2) minimize systemic toxicity when CNS benefit is improbable. The workshop systematically evaluated permeability assessment modalities, including drug physicochemical properties, in vitro blood-brain barrier models, and penetration into cerebrospinal fluid and normal rodent brain. Methodological approaches to determine requisite NEB drug concentrations and approaches to measuring NEB pharmacokinetics and pharmacodynamics were examined. This culminated in developing the Non-Enhancing Brain Permeability Index (NEBPI), which assigns therapeutic agents to 3 categories: sufficiently permeable, insufficiently permeable, or impermeable. The NEBPI provides a standardized framework to assist investigators and regulatory agencies to evaluate NEB penetration before human efficacy studies are initiated for agents that require direct tumor contact. Assessing NEB drug penetration is critical to improving outcomes in CNS tumors and reducing the incidence of brain metastases in systemic malignancies.
CTNI-30. ALLIANCE A071601: PHASE II TRIAL OF BRAF/MEK INHIBITION IN RECURRENT PAPILLARY CRANIOPHARYNGIOMAS
Geyer, Susan, Kabat, Brian, Gerstner, Elizabeth R. , Choi, Yoon Jae, Fuente, Macarena I. de la , Lesser, Glenn J. , Kumthekar, Priya , Vora, Shivangi, Knopp, Michael V. , Iafrate, A. John , Brown, Paul D. , Barker, Frederick G., Brastianos, Priscilla K. , Reed, Sarah, Kaufmann, Timothy J. , Barbaro, Marissa , Cahill, Daniel P. , Shih, Helen A. , Santagata, Sandro , Galanis, Evanthia

Neuro-Oncology | November 11, 2025 | Volume: 27 | Issue: Supplement_5 | Pages: v132-v133

10.1093/neuonc/noaf201.0527 Get It

Abstract BACKGROUND Craniopharyngiomas are a rare tumor along the pituitary-hypothalamic axis. Genetic analysis revealed that 95% of papillary craniopharyngiomas (PCP) have BRAF V600E mutations (Brastianos et al. Nature Genetics 2014). We previously reported that BRAF/MEK inhibition was associated with significant anti-tumor activity in newly-diagnosed PCP patients (Brastianos et al. NEJM 2023). We have now evaluated the efficacy of vemurafenib/cobimetinib in a separate cohort of patients with recurrent PCP whose tumors progressed after prior radiation. METHODS In this multicenter, NCI-sponsored cooperative group trial, patients with histologically confirmed BRAF-positive PCP who progressed after radiation were treated with vemurafenib/cobimetinib. The primary endpoint of response rate (RR) based on centrally determined imaging data was to be evaluated in 16 patients, where a partial response was defined as ≥20% decrease in volume. This single arm, Simon two-stage phase 2 trial had 89% power to detect a true RR ≥ 30% (vs. null 5%; α=0.04). In this design, 3 or more observed responses in 16 evaluable patients would be considered evidence of promising activity. RESULTS Of the planned 16 patients, a total of 5 patients enrolled before the study was closed due to slow accrual. Median follow-up was 50 months (95% CI: 32 to not yet reached). Based on volumetric response criteria, all 5 patients had a response to treatment (100%; 95% CI: 47.8% to 100%). To date, 2 patients progressed, one of whom died 22 months after study entry. This cohort met the criteria for efficacy under the original design with &gt;3 responders. No grade 4 or 5 toxicities were observed. CONCLUSIONS Vemurafenib/cobimetinib resulted in an objective response in all patients with previously treated PCP. The study met primary endpoint, similar to that reported for previously untreated PCP. Thus, BRAF/MEK inhibitors could be an effective tool for previously treated PCP and warrants further evaluation. SUPPORT U10CA180821; U10CA180882; Genentech, https://acknowledgments.alliancefound.org;ClinicalTrials.gov: NCT03224767
Defining the Role of the Advanced Practice Provider Within the National Cancer Institute Community Oncology Research Program
Braun‐Inglis, Christa , Dressler, Emily V. , Myers, Jamie , Benson, Al B. , Flannery, Marie , Good, Marjorie J. , Denicoff, Andrea , Berenberg, Jeffrey L. , DeTroye, Alisha , O'Brien, Bridget, Kottschade, Lisa A. , Omatsu, Dee Ann, Foust, Melyssa , Lesser, Glenn J. , Braun-Inglis, Christa M , Myers, Jamie S , Good, Marjorie , Kottschade, Lisa A , Nightingale, Chandylen L , Dressler, Emily V , Kittel, Carol , Nightingale, Chandylen L.

JCO Oncology Practice | January 4, 2024 | Volume: 20 | Issue: 2 | Pages: 239-246

10.1200/op.23.00501 Get It

PURPOSE Oncology advanced practice providers (APPs), including nurse practitioners, clinical nurse specialists, physician assistants, and clinical pharmacists, contribute significantly to quality cancer care. Understanding the research-related roles of APPs in the National Cancer Institute's (NCI) Community Oncology Research Program (NCORP) could lead to enhanced protocol development, trial conduct, and accrual. METHODS The 2022 NCORP Landscape Assessment Survey asked two questions about the utilization and roles of APPs in the NCORP. RESULTS A total of 271 practice groups completed the 2022 survey, with a response rate of 90%. Of the 259 nonpediatric exclusive practice groups analyzed in this study, 92% used APPs for clinical care activities and 73% used APPs for research activities. APPs most often provided clinical care for patients enrolled in trials (97%), followed by assistance with coordination (65%), presenting/explaining clinical trials (59%), screening patients (49%), ordering investigational drugs (37%), and consenting participants (24%). Some groups reported APPs as an enrolling investigator (18%) and/or participating in institutional oversight/selection of trials (15%). Only 5% of NCORP sites reported APPs as a site primary investigator for trials, and very few (3%) reported APPs participating in protocol development. CONCLUSION Practice groups report involving APPs in clinical research within the NCORP network; however, opportunities for growth exists. As team-based care has enhanced clinical practice in oncology, this same approach can be used to enhance successful research. Suggested strategies include supporting APP research-related time, recognition, and education. The findings of this survey and subsequent recommendations may be applied to all adult oncology practices that participate in clinical research.
INNV-32. RELIABILITY OF SERIAL NEUROPATHOLOGICAL ASSESSMENT TO DIFFERENTIATE TUMOR PROGRESSION FROM PSEUDO-PROGRESSION IN GLIOMA
Khoury, Lara, Harrison, W.T.A. , Ramkissoon, Shakti, Stogner‐Underwood, Kimberly, Mott, Ryan T., Miller, James, Lesser, Glenn J. , Cramer, Christina K. , Laxton, Adrian W. , White, Jaclyn, Harrison, William, Chan, Michael David , Tatter, Stephen B. , Tavolara, Thomas Erol , Hsu, Fang‐Chi , Strowd, Roy E.

Neuro-Oncology | November 11, 2023 | Volume: 25 | Issue: Supplement_5 | Pages: v163-v164

10.1093/neuonc/noad179.0621 Get It

Abstract Histopathology is the gold standard for distinguishing tumor recurrence from treatment-induced necrosis but differentiating pseudoprogression from true recurrence is challenging in tumors with ambiguous morphological features. Prior research reported a 36% inter-rater agreement during suspected recurrence (Holdhoff et al., 2019). While serial radiographic and laboratory assessments are common, serial histopathological assessments are not. This study evaluated agreement and factors influencing assessment of active and inactive tumors through single and multiple time-point histopathological assessments. Patients who underwent initial and subsequent reoperation were identified, and their available histology slides were examined retrospectively. Four independent neuropathologists conducted two types of reviews: single time-point reviews using most recent biopsy/surgery slides, and multiple time-point reviews comparing images from initial and repeat biopsies taken 1-3 months apart. Neuropathologists completed a questionnaire assessing various tumor characteristics. Assignments were categorized as "active tumor," "treatment effect," or "unable to classify." 324 assessments were conducted (108 single time-point, 216 multiple time-point). Intraclass correlation coefficients for single vs. multiple time-point assessments were 0.72-0.93 for active tumors and 0.57-0.86 for inactive tumors. Pathologists' assessment of % inactive tumor was influenced by mitotic activity (p= 0.0028), cellularity (p&lt; 0.0001), hyalinized vessels (p= 0.0019), and necrosis (p= 0.0046). Evaluation of % active tumor was influenced by hyalinized vessels (p= 0.0006), mitotic activity (p&lt; 0.0001), cellularity (p&lt; 0.0001), and microvascular proliferation (p= 0.0093), with the latter three factors specifically affecting final sign-out pathology. Serial histopathological assessment didn’t affect determination of % active or inactive tumor. No association between % inactive tumor and fibrinoid necrosis for single time-point (p= 0.34) but a strong negative association was seen for serial assessment (p= 0.0006). Inter-rater agreement was higher for identifying active tumors than inactive tumors in both case reviews. Changes in necrosis between tissue samples in single vs. multiple timepoint assessments influenced pathologists' assessment of % inactive tumor.
CTNI-73. ALLIANCE A071601: PHASE II TRIAL OF BRAF/MEK INHIBITION IN NEWLY DIAGNOSED PAPILLARY CRANIOPHARYNGIOMAS
Twohy, Erin , Geyer, Susan, Gerstner, Elizabeth R. , Kabat, Brian, Thierauf, Julia , Ruff, Michael W. , Reardon, David A. , Cohen, Adam L. , Fuente, Macarena de la, Lesser, Glenn J. , Campian, Jian , Agarwalla, Pankaj K., Kumthekar, Priya , Mann, Bhupinder, Vora, Shivangi, Knopp, Michael, Iafrate, A. John , Brown, Paul D. , Barker, Frederick G., Brastianos, Priscilla K. , Kaufmann, Timothy J. , Tabrizi, Shervin , Bota, Daniela A. , Knopp, Michael V. , Curry, William T. , Cahill, Daniel P. , Shih, Helen A. , Santagata, Sandro , Galanis, Evanthia

Neuro-Oncology | November 11, 2023 | Volume: 25 | Issue: Supplement_5 | Pages: v94-v94

10.1093/neuonc/noad179.0355 Get It

Abstract BACKGROUND Craniopharyngiomas, primary brain tumors of the pituitary-hypothalamic axis, can cause significant clinical sequelae. Treatment using surgery, radiation, or both often entails significant morbidity. In prior work, we demonstrated that ninety-five percent of papillary craniopharyngiomas (PCP) harbor BRAF V600E mutations (Brastianos et al. Nature Genetics 2014). In this multicenter National Cancer Institute cooperative group trial (Alliance A071601), we evaluated the safety and efficacy of BRAF/MEK inhibition in patients with PCP without prior irradiation. METHODS Eligible patients, with measurable disease and whose PCP screened positively for BRAF mutations, without prior radiation, received the BRAF/MEK inhibitor combination vemurafenib/cobimetinib in 28-day cycles. The primary endpoint of objective response rate at 4 months based on centrally determined volumetric data was evaluated in 16 patients on this single arm phase 2 trial. RESULTS Based on volumetric response criteria by central radiology review, 15 of 16 patients (94%; 95% CI: 70% to 100%) had a durable objective partial response to therapy. Thus, this study met primary endpoint for overall response rate. The median tumor reduction was 91% (range of 68% to 99%). Median follow-up was 22 months (95% CI: 19 to 30 months) and median number of treatment cycles was 8. Median progression-free survival and duration of response were not yet reached. Three patients progressed during follow-up after therapy was discontinued; none have died. The sole non-responder stopped treatment after eight days due to toxicity. Grade 3 toxicities at least possibly related to treatment occurred in 12 patients (rash in 6 patients). Grade 4 toxicities were observed in two patients: hyperglycemia (n=1) and increased creatine phosphokinase (n=1). Three patients discontinued treatment for adverse events. CONCLUSIONS Our study indicates that BRAF/MEK inhibitors are a safe and effective treatment for PCP without prior irradiation. Support: U10CA180821, U10CA180882; U24CA196171, U10CA180868 (NRG); Genentech; . ClinicalTrials.gov Identifier: NCT03224767.
Long-Term Report of a Comprehensive Molecular and Genomic Analysis in NRG Oncology/RTOG 0424: A Phase II Study of Radiation and Temozolomide in High-Risk Grade II Glioma
Fleming, Jessica L. , Pugh, Stephanie L. , Fisher, Barbara J., Lesser, Glenn J. , Macdonald, David R., Bell, Erica H. , McElroy, Joseph , Becker, Aline Paixão , Timmers, Cynthia , Aldape, Kenneth , Rogers, Leland , Doyle, Thomas J. , Werner‐Wasik, Maria, Bahary, Jean-Paul , Tsai, Ya-Yu , D’Souza, David , Sneed, Penny K. , Kwok, Young , Won, Minhee , Chakravarti, Arnab , Chakravarti, Arnab , Chakravarti, Arnab , Laack, Nadia N. , Mehta, Minesh P.

JCO Precision Oncology | September 1, 2021 | Volume: No volume available | Issue: 5 | Pages: 1397-1407

10.1200/po.21.00112 Get It

PURPOSE This study sought to determine the prognostic significance of the WHO-defined glioma molecular subgroups along with additional alterations, including MGMT promoter methylation and mutations in ATRX, CIC, FUBP1, TERT, and TP53, in NRG/RTOG 0424 using long-term follow-up data. METHODS Mutations were determined using an Ion Torrent sequencing panel. 1p/19q co-deletion and MGMT promoter methylation were determined by Affymetrix OncoScan and Illumina 450K arrays. Progression-free survival (PFS) and overall survival (OS) were estimated using the Kaplan-Meier method and tested using the log-rank test. Hazard ratios were calculated using the Cox proportional hazard model. Multivariable analyses (MVAs) included patient pretreatment characteristics. RESULTS We obtained complete molecular data to categorize 80/129 eligible patients within the WHO subgroups. Of these, 26 (32.5%) were IDHmutant/co-deleted, 28 (35%) were IDHmutant/non-co-deleted, and 26 (32.5%) were IDHwild-type. Upon single-marker MVA, both IDHmutant subgroups were associated with significantly better OS and PFS ( P values < .001), compared with the IDHwild-type subgroup. MGMT promoter methylation was obtained on 76 patients, where 58 (76%) were methylated and 18 (24%) were unmethylated. Single-marker MVAs demonstrated that MGMT promoter methylation was statistically significant for OS ( P value < .001) and PFS ( P value = .003). In a multimarker MVA, one WHO subgroup comparison ( IDHmutant/co-deleted v IDHwild-type) was significant for OS ( P value = .045), whereas MGMT methylation did not retain significance. CONCLUSION This study reports the long-term prognostic effect of the WHO molecular subgroups, MGMT promoter methylation, and other mutations in NRG/RTOG 0424. These results demonstrate that the WHO molecular classification and MGMT both serve as strong prognostic indicators, but that MGMT does not appear to add statistically significant prognostic value to the WHO subgrouping, above and beyond IDH and 1p/19q status.
Lactoferrin Supplementation For Taste And Smell Abnormalities Among Patients Receiving Cancer Chemotherapy
Lesser, Glenn J. , Irby, Megan B. , Taylor, Richard J. , Case, Douglas, Wang, Aili , Dietrich, Andrea, Duncan, Susan E. , Taylor, Richard, Snavely, Anna C.

No container title available | July 7, 2021 | Volume: No volume available | Issue: No issue available | Pages: No page available

10.21203/rs.3.rs-603866/v1 Get It

Abstract Purpose: Taste and smell abnormalities (TSA) are common in patients receiving chemotherapy and may lead to altered nutritional intake, treatment withdrawal, and impaired quality of life. Lipid peroxidation in the oral cavity is one cause of TSA. Lactoferrin (LFN), an iron-binding salivary protein, reduces production of lipid oxidation byproducts and has been shown to reduce perception of unpleasant flavors. To assess the feasibility of LFN as a treatment for TSA, we conducted pilot investigations among patients with cancer who self-reported TSA following onset of chemotherapy. The primary objective was to assess change in subjective taste and smell perception from baseline to completion of 30-days of LFN supplementation.Methods: Patients were treated with 750mg LFN daily for 30 days and followed for an additional 30 days without LFN. TSA was measured via the taste and smell questionnaire (TSQ) including taste (score 0-10), smell (score 0-6), and composite scores (0-16, 0=no TSA) at baseline, day 30, and day 60.Results: 26 patients enrolled; 19 remained on study at day 30 and 17 at day 60. Baseline mean TSQ scores were 6.5 (taste), 3.1 (smell) and 9.6 (composite). By day 30, mean composite TSQ score improved by 1.7 (p=0.018); taste and smell improved by 0.6 (p=.062) and 1.1 (p=.042) respectively. From baseline to day 60, mean composite TSQ score improved by 3.8 (p<.0001); taste and smell improved by 1.9 (p=.001) and 1.8 (p=.003). Conclusions: Further evaluation of LFN is warranted to determine its value for improving self-reported TSA among patients receiving chemotherapy.
Alliance A071601: Phase II trial of BRAF/MEK inhibition in newly diagnosed papillary craniopharyngiomas.
Twohy, Erin , Geyer, Susan, Gerstner, Elizabeth R. , Ruff, Michael W. , Bota, Daniela A. , Reardon, David A. , Cohen, Adam L. , Fuente, Macarena I. de la, Lesser, Glenn J. , Campian, Jian , Agarwalla, Pankaj K., Kumthekar, Priya , Brown, Paul D. , Barker, Frederick G., Brastianos, Priscilla K. , Kaufmann, Timothy J. , Cahill, Daniel P. , Shih, Helen A. , Santagata, Sandro , Galanis, Evanthia

Journal of Clinical Oncology | June 2, 2021 | Volume: 39 | Issue: 15_suppl | Pages: 2000-2000

10.1200/jco.2021.39.15_suppl.2000 Get It

2000 Background: Craniopharyngiomas, a rare brain tumor along the pituitary-hypothalamic axis, can cause significant clinical sequelae. Surgery and radiation, the only effective treatments, can cause significant morbidity. Genetic analysis of craniopharyngiomas revealed that 95% of papillary craniopharyngiomas (PCP) have BRAF V600E mutations (Brastianos et al. Nature Genetics 2014). We evaluated the efficacy of BRAF/MEK inhibition in patients (pts) with previously untreated PCP. Methods: Eligible pts without prior radiation whose PCP screened positively for BRAF mutations were treated with oral vemurafenib/cobimetinib in 28-day cycles. The primary endpoint of response rate (RR) based on centrally determined volumetric data was evaluated in 16 pts, where a partial response was defined as >20% decrease in volume. This single arm, Simon two-stage phase 2 trial had 89% power to detect a true RR of at least 30% (vs. the null RR 5%; alpha=0.04). In this design, 3 or more observed volumetric responses in 16 evaluable pts would be considered promising activity. Results: In the 16 pts evaluated, 56% were female, and the median age was 49.5 years. Median follow-up was 22 months (95% CI: 16-26.5) and median number of treatment cycles was 8. Three patients progressed after therapy was discontinued and none have died. Based on volumetric response criteria, 14 of 15 pts with volumetric data available for central review had response to therapy (93%; 95% CI: 68% to 99.8%). Of 16 patients evaluable based on local review, 15 had response to therapy (93.75%; 95% CI: 70% to 99.8%). The median tumor reduction was -83% (range: -52% to -99%). The one nonresponder received 2 days of treatment before coming off therapy due to toxicity. Median progression-free survival was not reached. Grade 3 toxicities at least possibly related to treatment occurred in 12 pts (rash in 6 pts). Grade 4 toxicities were observed in two pts: hyperglycemia (n=1) and increased CPK (n=1). Three pts discontinued treatment for adverse events. Conclusions: Vemurafenib/cobimetinib resulted in an objective response in all pts who received 1 or more cycles of therapy. Our study indicates that BRAF/MEK inhibitors could be a powerful tool in the treatment of previously untreated PCP and warrants further evaluation in larger studies. A second arm of this study is enrolling pts with progressive PCP after prior radiotherapy. Support: U10CA180821, U10CA180882; U24CA196171, U10CA180868 (NRG); Genentech; https://acknowledgments.alliancefound.org. Clinical trial information: NCT03224767.