Management of testicular germ cell tumors.

Over the past half century, advancements in treatment have led to cures in an overwhelming majority of patients with testicular germ cell tumors. Astute clinical decision-making, informed by the abundant data from published clinical trials, is essential for achieving a cure whenever possible and minimizing the toxicity of treatment. Important remaining challenges include reducing the risk of secondary malignancies and other late effects of chemotherapy and radiation therapy, and developing curative treatments for patients with cancer that is refractory to current therapies. This article reviews the current treatment landscape and highlights recent discoveries in diagnosis and staging, emerging biomarkers for disease, and treatment for relapsed/refractory disease. Treatment algorithms for testis cancer are complex and clinicians should apply them carefully, not only to optimize shortterm, disease-related outcomes, but also to maximize long-term survival and quality of life.

Chemotherapy with atezolizumab for small cell or neuroendocrine carcinoma of the prostate: A single institution experience.

INTRODUCTION: Chemotherapy in combination with immunotherapy has a proven survival benefit compared to chemotherapy alone in extensive stage small cell lung cancer (SCLC) and is the new standard of care. Since extrapulmonary small cell carcinomas (SCCs) are less common, treatment paradigms are reasonably extrapolated from SCLC regimens. We examined our institution's experience utilizing the combination of chemotherapy and immunotherapy (as used in SCLC) for SCC and neuroendocrine carcinoma of the prostate. METHODS: Utilizing an institutional database search tool, we queried the electronic medical record to identify patients with SCC or neuroendocrine carcinoma of the prostate who had been treated with atezolizumab and chemotherapy. We recorded patient characteristics, including age, pathology, and disease extent. Treatment characteristics included number of prior treatments, use of concominant androgen deprivation, number of cycles of immunotherapy, and prior systemic therapies (including those for adenocarcinoma of the prostate). Progression free survival (PFS) and overall survival (OS) were the primary outcomes. RESULTS: We identified seven men who received atezolizumab for metastatic prostate cancer with a small cell or neuroendocrine component. In six of the seven patients, the combination of carboplatin, etoposide, and atezolizumab was the first-line of treatment after diagnosis of small cell or neuroendocrine carcinoma. Two of the seven patients had de novo small cell/neuroendocrine pathology, while the other five had transformation from a preexisting adenocarcinoma. In the patients who received chemotherapy plus immunotherapy in the first-line setting, at a median follow-up of 6.5 months (range: 1.5-15.1) the median PFS was 3.4 months and median OS was 8.4 months. CONCLUSION: Small cell or neuroendocrine carcinoma of the prostate was associated with poor survival outcomes despite adding immunotherapy (atezolizumab) to chemotherapy (carboplatin and etoposide). To our knowledge, there has been no demonstrable benefit of adding immunotherapy to chemotherapy in this setting.

Changes in Health and Well-Being during Residents' Training.

OBJECTIVES: Previous studies have characterized the negative effects of graduate medical education on physicians; however, there is limited longitudinal data on how physicians' well-being changes during their training. This study aimed to demonstrate and quantify changes to trainees' wellness and health habits during the course of their first 2 years of graduate medical education. METHODS: A longitudinal survey study of postgraduate year 1 trainees at the Cleveland Clinic was administered at 3 time points: the initial survey during orientation week, a second survey at 1 year, and a final survey at 2 years. RESULTS: Of the 170 trainees contacted, 59 (35%) completed the initial survey and 34 (58%) completed the first follow-up survey. Between the initial survey and the first follow-up survey, respondents reported that their health was worse than the prior year (P < 0.001). They also reported sleeping on average 1 hour less per night and exercising on average one fewer day per week. The number of individuals who reported not eating breakfast increased by 22%, whereas the number of individuals eating out at lunch more than doubled. Twenty-seven people completed the second follow-up survey. Between the first follow-up survey and the final survey, respondents gained on average 2.12 lb (P = 0.039). Breakfast, lunch, and sleeping habits persisted through the second follow-up survey. CONCLUSIONS: Residents' health and wellness habits deteriorated during internship and did not improve in the second year of residency. Efforts to promote healthy habits in this population should be a priority.

Platinum ineligibility and survival outcomes in patients with advanced urothelial carcinoma receiving first-line treatment.

BACKGROUND: This study examined real-world patients with locally advanced or metastatic urothelial carcinoma considered ineligible for platinum-containing chemotherapy in the first-line setting. METHODS: This retrospective observational study used data from a nationwide (United States) de-identified patient-level electronic health record-derived database. Eligible adults (aged 18 years and older) had a locally advanced or metastatic urothelial carcinoma diagnosis on or after January 1, 2016, and initiated first-line systemic treatment at least 90 days before December 31, 2021. Platinum ineligibility was defined as Eastern Cooperative Oncology Group performance status of at least 3, creatinine clearance less than 30 mL/min, or Eastern Cooperative Oncology Group performance status of 2 and creatinine clearance of less than 45 mL/min. Overall survival and real-world progression-free survival (PFS) were summarized using the Kaplan-Meier method. RESULTS: The overall population comprised 4270 patients; 477 (11%) were considered platinum ineligible, 262 (55%) received a first-line programmed cell death 1 or programmed cell death ligand 1 immune checkpoint inhibitor, and 118 (25%) received platinum-based chemotherapy. A total of 2335 (55%) patients were platinum eligible; 677 (29%) received a first-line programmed cell death 1 or programmed cell death ligand 1 inhibitor, and 1229 (53%) received platinum-based chemotherapy. Median overall survival was 13.3 months (95% confidence interval [CI] = 12.4 to 14.8 months) in platinum-eligible and 5.1 months (95% CI = 4.2 to 6.4 months) in platinum-ineligible patients. Median PFS was shorter in platinum-ineligible (3.4 months; 95% CI = 2.9 to 4.0 months) vs platinum-eligible patients (5.9 months; 95% CI = 5.5 to 6.2 months) overall and when stratified by first-line therapy type. CONCLUSION: This real-world study has shown for the first time the treatment patterns and outcomes in newly diagnosed patients with locally advanced or metastatic urothelial carcinoma ineligible for platinum-based chemotherapy. These findings provide quantitative benchmarks for platinum ineligibility in the first-line advanced or metastatic urothelial carcinoma setting and highlight the need for novel therapy options.

Clinical Outcomes for Metastatic Renal Cell Carcinoma (mRCC) Patients Ineligible for Front-line Clinical Trials.

Clinical trials for immunotherapy-based regimens in metastatic renal cell carcinoma (mRCC) have extensive inclusion and exclusion criteria. We investigated the clinical outcomes in a real-world cohort of patients who would not have met the criteria for inclusion in front-line mRCC trials. Patients treated with ipilimumab/nivolumab and axitinib/pembrolizumab for front-line mRCC were identified and divided into clinical trial eligible (CTE) and clinical trial ineligible (CTI) cohorts based on key inclusion or exclusion criteria from their respective Phase-3 registration trials. Clinical outcomes were compared in CTE and CTI cohorts. A total of 62 patients treated with axitinib/pembrolizumab and 103 treated with ipilimumab/nivolumab were identified. The International Metastatic RCC Database Consortium (IMDC) criteria were similar across CTE and CTI patients in axitinib/pembrolizumab and ipilimumab/nivolumab cohorts. In the axitinib/pembrolizumab cohort (n = 62), 24 (39%) patients were CTI. The major reasons for the ineligibility were lab abnormalities (n = 11), histology (n = 9), and brain metastases (n = 3). There was no significant difference in response rates (P = 0.08). The median progression-free survival (PFS) was numerically longer in CTE patients (28 vs 12 months; P = 0.09). The overall survival (OS) was higher in the CTE patients (P = 0.02). In the ipilimumab/nivolumab cohort (n = 103), 59 (57%) were CTI. The most common reasons for ineligibility were brain metastases (n = 18), lab abnormalities (n = 16), and histology (n = 16). There was no significant difference in response rates (P = 0.22). However, PFS (P = 0.003) and OS (P < 0.0001) were higher in the CTE patients. In conclusion, many real-world patients are ineligible for RCC clinical trials and had worse outcomes when compared to trial-eligible patients. Additional treatment options are needed for these patients, as well as strategies to include them in prospective trials.

Risk of Thromboembolism in Patients Receiving Immunotherapy-Based Combinations as Front-Line Therapy for Metastatic Renal Cell Carcinoma.

BACKGROUND: Most patients with treatment-naïve metastatic renal cell carcinoma (mRCC) receive combination-based immunotherapy with either 2 immune-oncology checkpoint inhibitors (IO/IO) or an IO agent in combination with a vascular endothelial growth factor receptor (VEGF-R) tyrosine kinase inhibitor (IO/TKI). The rates of thromboembolism (TE) in these cohorts are not clearly described and can potentially impact decision-making between IO/IO and IO/TKI. METHODS: We conducted a retrospective investigation of patients with treatment-naïve mRCC treated with IO-based combinations between January 2015 and April 2021 at the Cleveland Clinic. TE events, including venous and arterial, were identified in each group. Competing risk regression was done to identify factors associated with the development of TE following therapy, with all-cause mortality treated as a competing event. RESULTS: Of 180 patients identified, 77 (43%) received IO/TKI and 103 (57%) received IO/IO. Median age was 65 years, 75% were male, and 80% had clear cell histology. Baseline characteristics were similar between the 2 groups. At a median follow-up of 22.0 months, 10.0% of all patients had a TE. The one-year incidence of TE was 8.1% (95% CI: 3.3%-15.8%) with IO/TKI and 9.8% (95% CI: 5.0%-16.5%) with IO/IO and was not significantly different between the 2 groups (HR 0.89, 95% CI: 0.35%-2.28%). Occurrence of TE was associated with decreased overall survival regardless of IO/IO or IO/TKI therapy (HR 2.80, 95% CI: 1.57-5.02). There was no difference in incidence of TE based on patient age, gender, prior history of TE, International Metastatic Renal Cell Carcinoma (IMDC) risk group, or Khorana score. CONCLUSIONS: Incidence of TE is similar between IO/IO and IO/TKI regimens in treatment-naïve mRCC and is also associated with decreased overall survival. While risk of TE may not guide decision-making in choice of front-line mRCC therapy, careful attention should be given to the high risk of TE in this population.

Safety and Efficacy Outcomes in Immune Checkpoint Inhibitor-Treated Patients With Metastatic Urothelial Carcinoma Requiring Treatment Interruption or Discontinuation Due to Immune-Related Adverse Events.

INTRODUCTION: As most patients with metastatic urothelial carcinoma (mUC) will be treated with immune checkpoint inhibitors (ICI), familiarity with their associated immune-related adverse events (irAEs) is critical. We describe the characteristics and outcomes of ICI-treated mUC patients who experienced irAEs requiring treatment interruption (TI) or permanent discontinuation. MATERIALS AND METHODS: ICI-treated mUC patients who developed grade ≥2 irAEs were reviewed. Clinical-, treatment-, and toxicity-related data were evaluated. Toxicity was graded per common terminology for categorization of adverse events v5.0. Cohorts were divided into patients who underwent ICI rechallenge and those who required permanent ICI discontinuation. Time to treatment interruption (TTI), time to next treatment, and duration of clinical benefit were assessed descriptively. Progression-free survival and overall survival (OS) were estimated using Kaplan-Meier methodology. RESULTS: Of 200 ICI-treated mUC patients at Cleveland Clinic between October 2015 and October 2020, 16 (8%) experienced ≥ grade 2 irAEs necessitating TI. Median TTI among all patients was 6.5 months (range, 1-19). Eleven patients (69%) required corticosteroids. ICI were held and rechallenged in 10 patients (62%) and permanently discontinued in 6 patients (38%). Of the 10 ICI-rechallenged patients, 7 (70%) experienced another irAE upon rechallenge with median time to irAE recurrence of 2.9 months (range, 0.1-10.9); 3 (30%) eventually discontinued ICI due to recrudescent irAEs. Four (40%) of the 10 ICI-rechallenged patients received subsequent therapy. Five (83%) of the 6 patients who permanently discontinued ICI demonstrated durable clinical benefit off therapy with median duration of clinical benefit 17.7 months (range, 14.2-55.2). Two-year OS was 40% (95% CI: 19%-86%) in the ICI rechallenge cohort and 67% (95% CI: 38%-100%) in the permanent discontinuation cohort. CONCLUSION: ICI-treated mUC patients who developed irAEs requiring TI had a high rate of subsequent irAEs upon ICI rechallenge. Importantly, patients who permanently discontinued ICI due to irAE demonstrated durable clinical benefit off treatment.

Phase II Trial of Intermittent Therapy in Patients with Metastatic Renal Cell Carcinoma Treated with Front-line Ipilimumab and Nivolumab.

INTRODUCTION: The combination of ipilimumab/nivolumab is approved for patients with treatment-naïve, intermediate-, and poor-risk metastatic renal cell carcinoma (mRCC), but duration of therapy and safety/efficacy of reinduction at progression is unknown. A phase II trial of intermittent ipilimumab/nivolumab with reinduction at progression was conducted (NCT03126331). PATIENTS AND METHODS: Patients with treatment-naïve mRCC were treated with induction ipilimumab/nivolumab followed by up to 24 weeks of maintenance nivolumab. Patients who achieved a complete response (CR) or partial response (PR) were eligible for inclusion and entered a treatment-free observation period. Patients were restaged every 12 weeks. Patients with no disease progression (PD) remained off therapy. Upon PD, patients were re-challenged with 2 doses of ipilimumab/nivolumab every 3 weeks. Study objectives were to estimate success rate of observation in patients who achieve a CR/PR, and to assess toxicity in patients undergoing reinduction. The study accrued slower than expected and was closed prior to the anticipated accrual goal of 20 patients. RESULTS: Nine patients were included; 89% male, median age 57, 67% clear-cell histology, and 78% intermediate-risk by IMDC criteria. Response to ipilimumab/nivolumab followed by nivolumab maintenance prior to enrollment was 33% CR and 67% PR. Most (78%) patients have remained off therapy, with a median treatment-free interval (TFI) of 34.3 months (range, 8.7-41.8). Two patients had PD off therapy and received 2 cycles of reinduction ipilimumab and nivolumab. No grade 3 or greater toxicities occurred with reinduction. Both patients developed PD at their first scans after reinduction. CONCLUSION: This prospective study demonstrates that patients with a radiographic response to ipilimumab/nivolumab can have prolonged treatment-free intervals. Further studies of de-escalation strategies are warranted. TRIAL REGISTRATION: NCT03126331 [Date of registration 4/27/2017; https://clinicaltrials.gov/ct2/show/NCT03126331].

Lineage plasticity and treatment resistance in prostate cancer: the intersection of genetics, epigenetics, and evolution.

Androgen deprivation therapy is a cornerstone of treatment for advanced prostate cancer, and the development of castrate-resistant prostate cancer (CRPC) is the primary cause of prostate cancer-related mortality. While CRPC typically develops through a gain in androgen receptor (AR) signaling, a subset of CRPC will lose reliance on the AR. This process involves genetic, epigenetic, and hormonal changes that promote cellular plasticity, leading to AR-indifferent disease, with neuroendocrine prostate cancer (NEPC) being the quintessential example. NEPC is enriched following treatment with second-generation anti-androgens and exhibits resistance to endocrine therapy. Loss of RB1, TP53, and PTEN expression and MYCN and AURKA amplification appear to be key drivers for NEPC differentiation. Epigenetic modifications also play an important role in the transition to a neuroendocrine phenotype. DNA methylation of specific gene promoters can regulate lineage commitment and differentiation. Histone methylation can suppress AR expression and promote neuroendocrine-specific gene expression. Emerging data suggest that EZH2 is a key regulator of this epigenetic rewiring. Several mechanisms drive AR-dependent castration resistance, notably AR splice variant expression, expression of the adrenal-permissive 3ßHSD1 allele, and glucocorticoid receptor expression. Aberrant epigenetic regulation also promotes radioresistance by altering the expression of DNA repair- and cell cycle-related genes. Novel therapies are currently being developed to target these diverse genetic, epigenetic, and hormonal mechanisms promoting lineage plasticity-driven NEPC.

The Potential and Limitations of Precision Oncology: Lessons Learned from Whole-Exome Sequencing in an Exceptional Response to Everolimus in Advanced Renal Cell Carcinoma.

Through elucidating the genetic mechanisms of drug sensitivity, precision medicine aims to improve patient selection and response to therapy. Exceptional responders are patients that exhibit exquisite and durable responses to targeted therapy, providing a rare opportunity to identify the molecular basis of drug sensitivity. We identified an exceptional responder to everolimus, an oral inhibitor of the mammalian target of rapamycin (mTOR) pathway, in a patient with advanced renal cell carcinoma. Through whole-exome sequencing on pretreatment and metastatic tumor DNA, we identified alterations in several mTOR pathway genes, with several mutations implicated in mTOR activation. Importantly, these alterations are currently not included in commercially available next-generation sequencing panels, suggesting that precision medicine is still limited in its ability to predict responses to mTOR-targeted therapies. Further research to discover and validate predictive biomarkers of response to everolimus and other targeted therapies is urgently needed. Given the rarity of patients with exceptional responses to targeted agents, cooperative efforts to understand the molecular basis for these phenotypes are essential.

Outcomes of COVID-19 in Patients With Cancer: A Closer Look at Pre-Emptive Routine Screening Strategies.

PURPOSE: The benefit of routine pre-emptive screening for severe acute respiratory syndrome coronavirus 2 infections in patients with cancer before cancer-directed therapies is unclear. Herein, we characterize the outcomes of a cohort of patients with cancer who were diagnosed with COVID-19 by routine screening (RS) in comparison with those diagnosed on the basis of clinical suspicion or exposure history (nonroutine screening [NRS]). METHODS: A multisite prospective observational study was conducted at three major and five satellite campuses of the Mayo Clinic Cancer Center between March 18 and July 31, 2020. The primary outcome was COVID-19-related hospital admission. Secondary outcomes included intensive care unit admissions and all-cause mortality. RESULTS: Five thousand four hundred fifty-two patients underwent RS in the outpatient setting only, and 44 (0.81%) were diagnosed with COVID-19. RS detected 19 additional patients from the scheduled inpatient admissions for surgical or interventional procedures or inpatient chemotherapy. One hundred sixty-one patients were diagnosed with COVID-19 on the basis of NRS. COVID-19-related hospitalization rate (17.5% v 26.7%; P = .14), intensive care unit admission (1.6% v 5.6%; P = .19), and mortality (4.8% v 3.7%; P = .72) were not significantly different between the RS and NRS groups. In the multivariable analysis, age ≥ 60 years (odds ratio, 4.4; P = .023) and an absolute lymphocyte count ≤ 1.4 × 109/L (odds ratio, 9.2; P = .002) were independent predictors of COVID-19-related hospital admission. CONCLUSION: The COVID-19 positivity rate was low on the basis of RS. Comparing the hospital admission and mortality outcomes with the NRS cohort, there were no significant differences. The value of routine pre-emptive screening of asymptomatic patients with cancer for COVID-19 remains low.

Evaluating Unconscious Bias: Speaker Introductions at an International Oncology Conference.

PURPOSE: In a professional setting, the introduction of female speakers without their professional title may have an impact on the public's perception of the female speaker. We examined how professional titles were used during speakers' introductions at the ASCO Annual Meeting. METHODS: We conducted a retrospective, observational study of video-archived speaker introductions at the 2017 and 2018 ASCO Annual Meetings. A "professional address" was defined as the professional title followed by the speaker's full name or last name. Multivariable logistic regressions were used to identify factors associated with the form of address. RESULTS: Of 2,511 videos reviewed, 781 met inclusion criteria. Female speakers were addressed less often by their professional title compared with male speakers (62% v 81%; P < .001). Males were less likely to use a professional address when introducing female speakers compared with females when introducing male speakers (53% v 80%; P < .01). When women performed speaker introductions, no gender differences in professional address were observed (75% v 82%; P = .13). Female speakers were more likely to be introduced by first name only (17% v 3%; P < .001). Male introducers were more likely to address female speakers by first name only compared with female introducers (24% v 7%; P < .01). In a multivariable regression including gender, degree, academic rank, and geographic location of the speaker's institution, male speakers were more likely to receive a professional address compared with female speakers (odds ratio, 2.43; 95% CI, 1.71 to 3.47; P < .01). CONCLUSION: When introduced by men, female speakers were less likely to receive a professional address and more likely to be introduced by first name only compared with their male peers.

Analysis of Origins of Admission for Solid Tumor Oncology Inpatients: Disease Severity and Outcomes.

PURPOSE: Hospital transfers may affect clinical outcomes. Evaluation of admission by source of transfer, time of admission, and provider type may identify opportunities to improve inpatient outcomes. METHODS: We reviewed charts of patients admitted to the solid tumor oncology service between July and December 2014 from the Cleveland Clinic Foundation (CCF) Main Campus emergency department (ED), CCF Regional EDs, outside hospital (OSH) ED, OSH inpatient services, and CCF outpatient clinics. Data collected included time of admission, mortality and severity risk scores, and provider type. Risk factors were assessed for clinical outcomes, including activations of the Adult Medical Emergency Team, intensive care unit transfers, in-hospital mortality, and length of stay (LOS). RESULTS: Five hundred admissions were included. OSH inpatient transfers had significantly higher disease severity compared with all other origins of admission. OSH inpatient transfers demonstrated significantly longer LOS compared with all other origins of admission, and higher mortality rates compared with the outpatient direct admits and CCF Main Campus ED admits. After adjusting for disease severity and risk of mortality, OSH ED patients remained at higher risk for Adult Medical Emergency Team activation, OSH inpatient transfers had the longest LOS, and CCF Main Campus ED patients had the lowest risk of mortality. Time of admission and provider type were not associated with any of the outcomes. CONCLUSION: Oncology inpatients transferred from an outside health care facility are at higher risk for adverse outcomes. The magnitude of difference is lessened, but still significant, after adjustment for disease severity and risk of mortality.

Canadian C-spine Rule and the National Emergency X-Radiography Utilization Low-Risk Criteria for C-spine radiography in young trauma patients.

PURPOSE: The Canadian C-spine (cervical spine) Rule (CCR) and the National Emergency X-Radiography Utilization Low-Risk Criteria (NLC) are criteria designed to guide C-spine radiography in trauma patients. It is unclear how these 2 rules compare with young children. METHODS: This study retrospectively examined case-matched trauma patients 10 years or younger. Two cohorts were identified-cohort A where C-spine imaging was performed and cohort B where no imaging was conducted. The CCR and NLC criteria were then applied retrospectively to each cohort. RESULTS: Cohort A contained 125 cases and cohort B with 250 cases. Seven patients (3%) had significant C-spine injuries. In cohort A, NLC criteria could be applied in 108 (86.4%) of 125 and CCR in 109 (87.2%) of 125. National Emergency X-Radiography Utilization Low-Risk Criteria suggested that 70 (58.3%) cases required C-spine imaging compared to 93 (76.2%) by CCR. National Emergency X-Radiography Utilization Low-Risk Criteria missed 3 C-spine injuries, and CCR missed one. In cohort B, NLC criteria could be applied in 132 (88%) of 150 and CCR in 131 (87.3%) of 150. The NLC criteria identified 8 cases and CCR identified 13 cases that would need C-spine radiographs. Fisher's 2-sided Exact test demonstrated that CCR and NLC predictions were significantly different (P = .002) in both cohorts. The sensitivity of CCR was 86% and specificity was 94%, and the NLC had a sensitivity of 43% and a specificity of 96%. CONCLUSIONS: Although CCR and NLC criteria may reduce the need for C-spine imaging in children 10 years and younger; they are not sensitive or specific enough to be used as currently designed.

GCP-mediated growth inhibition and apoptosis of prostate cancer cells via androgen receptor-dependent and -independent mechanisms.

BACKGROUND: Genistein combined polysaccharide (GCP) is a nutritional supplement that can inhibit prostate cancer growth experimentally and clinically. It is composed predominantly of the isoflavones genistein, daidzein, and glycitein, which have anti-cancer properties. Although genistein is well studied, the properties of GCP are not well defined. The goal of this work was to better characterize the signaling pathways impacted by GCP in an effort to optimize its efficacy. METHODS: Cell growth and apoptosis were evaluated by MTS proliferation, caspase-based assays, and flow cytometry. Modulation of androgen receptor (AR) levels and activation status of signaling molecules were monitored by immunoblot analysis. AR function was measured by evaluating prostate-specific antigen (PSA) message and protein levels and by reporter assays. RESULTS: GCP inhibited proliferation of androgen-dependent LNCaP and androgen-independent LNCaP-p53(GOF) and 22Rv1 cell lines in a dose-dependent manner and cells were more responsive in the presence of androgen. GCP markedly suppressed mTOR-p70S6K signaling while Akt and p53 were only modestly modulated. GCP significantly attenuated androgen signaling as evidenced by diminished AR protein levels and a consequent reduction in transcriptional activity and PSA expression. AR expression was enhanced by de-repression of translation with inhibitors of PI3K-Akt-mTOR signaling and by inhibition of proteasome-dependent degradation. Neither inhibitor could counteract GCP-mediated AR downregulation, suggesting the involvement of a mechanism(s) independent of these pathways. CONCLUSIONS: Our results suggest that GCP mediates growth inhibition and apoptosis through multiple mechanisms including (1) molecular mimicry of androgen ablation (via AR downregulation) and (2) by providing an AR-independent, pro-apoptotic signal (mTOR inhibition).