Real-World Toxicity of Conventional Versus Hypofractionated Definitive Prostate Radiotherapy across a Large, Diverse, Academic and Community-Based Enterprise

PURPOSE/OBJECTIVE(S)

Over the past 10-15 years there has been increasing adoption of moderate hypofractionation (HF) for definitive prostate radiotherapy as compared to conventional fractionation (CF). Based on several randomized trials hypofractionation results in equivalent treatment efficacy with similar rates of long-term toxicity. However, some studies suggest higher acute GI toxicity with moderate hypofractionation. We sought to compare the rates of toxicity between these two groups across our enterprise including 16 community-based practices and one academic NCI-designated comprehensive cancer center.

MATERIALS/METHODS

We retrospectively extracted radiation treatment intent from our network-wide clinical pathways for patients diagnosed with prostate cancer between 3/2019 and 10/2022. Patients treated after prostatectomy and those treated with brachytherapy or SBRT were excluded. For the remaining 1529 patients treated with either conventional fractionation or moderate hypofractionation, we identified and merged physician-graded toxicity data using CTCAE version 5.0 recorded in their electronic medical record at each weekly on-treatment visit and follow-up. A total of 1051 patients had toxicity data available. Rates of toxicities were then compared between the cohort of patients who received CF and those who HF using the Chi-square test.

RESULTS

Of the 1051 patients, 450 (43%) received CF and 601 (57%) received HF. These patients were treated by 40 different radiation oncologists (median patients per physician = 18, interquartile range = 7-35). Median age in the CF and HF cohorts was 71 (IQR: 66-76) and 71 (IQR: 66-77; p = 0.51), respectively. The CF cohort had more patients with Gleason 8+ disease (39% vs 19%; p<0.01), PSA >20 (26% vs 11%; p<0.01), or T3a+ (18% vs 8%; p<0.01). Rates of any grade 2+ toxicity were significantly higher in patients who received HF at 45.8% vs 39.6% for those treated with CF (p = 0.04). However, the respective rates of any grade 3+ toxicity were no different at 2.0% vs. 1.8% (p = 0.80). The difference in grade 2 toxicities appeared to be primarily driven by the rates of urinary frequency at 27.1% vs. 17.8% (p<0.01) and prostatic obstruction 14.8% vs. 10.2%, p = 0.03). Rates of grade 2 diarrhea were worse with MF at 5.3% vs. 2.8% for CF (p = 0.04). There were no significant differences between HF and CF in the rates of grade 2 dysuria (6% vs 5.2%), urinary urgency (6.5% vs. 4.2%), proctitis (3.0% vs. 3.6%), urinary incontinence (0.5% vs. 1.3%), rectal bleeding (0.3% vs. 0%), hematuria (0% vs. 0.4%), and fatigue (14.1% vs. 15.1%).

CONCLUSION

In this large network-wide analysis, toxicity was slightly increased among patients with prostate cancer treated with HF compared to CF, consistent with published randomized data. However, the increased toxicity appeared to be primarily GU rather than GI. This study demonstrates the feasibility of analyzing impacts of treatment decisions on a large scale using real-world data through an integrated network of practices.

Autologous Stem Cell Transplantation with Intensity Modulated Total Body Irradiation Conditioning for Systemic Sclerosis

PURPOSE/OBJECTIVE(S)

Based on the seminal SCOT trial, autologous stem cell transplantation (HSCT) using myeloablative total body irradiation (TBI) and anti-thymocyte globulin (ATG) as a conditioning regimen has become a standard treatment option for certain patients with systemic sclerosis (SSc). In patients with SSc, normal organs are more radiosensitive and prone to compromised function, and therefore lungs and kidneys require dose reduction. With traditional techniques, TBI requires heavy and thick physical blocks, which can be cumbersome and have poor reproducibility. We hypothesized that intensity modulated radiation therapy (IMRT) TBI compared to standard anteroposterior (AP)/posteroanterior (PA) TBI would facilitate improvements in dosimetry and reproducibility (due to not requiring physical blocks) without compromising outcomes. Herein, we report a single-institution retrospective analysis of patients with SSc treated with an IMRT TBI.

MATERIALS/METHODS

Patients with SSc who underwent HSCT with TBI between 2017 and 2022 were eligible. All patients underwent conditioning with equine ATG, cyclophosphamide 120 mg/kg, and IMRT TBI administered twice-daily to a total dose of 800 cGy in 200 cGy fractions. A minimum of 80% of the PTV was to receive prescription dose. Mean lung and kidney dose were to be less than 200 cGy. Patients were then replanned using an AP/PA technique for dosimetric comparison. The primary endpoint was planning target volume (PTV), lung, and kidney dosimetry. Secondary endpoints included event-free survival (EFS), overall survival (OS), disease-modifying antirheumatic drug-free survival (DMARD-FS), treatment related mortality (TRM), and toxicity.

RESULTS

A total of 14 patients were eligible for our analysis. On dosimetric analysis, the mean dose to the PTV was significantly higher on the IMRT compared to the AP/PA plans (809.4 cGy versus 728.5 cGy, p<0.001). The mean dose to the lungs (239.5 cGy versus 443.9 cGy, p<0.001) and kidneys (204.9 cGy versus 281.2 cGy, p<0.001) was significantly lower. Median follow-up was 34.6 months (1.0-51.7 months). There was one case of TRM secondary to respiratory failure. The 24-month OS, EFS, and DMARD-FS estimates were 92.9%, 74.3%, and 70.0%, respectively. Three patients experienced adverse events, which included respiratory failure (n = 1), renal failure (n = 1), and death (n = 1). No patients experienced clinically significant pneumonitis or nephritis that were deemed to be a likely consequence of TBI. Five patients subsequently initiated DMARDs, but three did so due to worsening skin symptoms without other major organ dysfunction.

CONCLUSION

Use of IMRT TBI as part of the conditioning regimen for HSCT for SSc yields improved dosimetry relative to a standard AP/PA technique, with efficacy and toxicity outcomes comparable with published data. This technique should be considered for patients undergoing HSCT for SSc and warrants inclusion in prospective trials for SSc that involve TBI.

Pilot Study of a Novel Ring Gantry-Based PET/CT Linear Accelerator in Patients with Prostate Cancer Receiving [18F]-DCFPyL for PSMA PET Imaging

PURPOSE/OBJECTIVE(S)

The RefleXion X1® system is a hybrid PET imaging-radiotherapy system that uses real-time positron emissions from a PET tracer to deliver biologically guided radiotherapy (BgRT). This study (NCT05470699) evaluated the hypothesis that the X1 PET imaging subsystem would be able to detect [18F]-DCFPyL PSMA PET signal sufficient to generate a deliverable BgRT plan in patients with prostate cancer.

MATERIALS/METHODS

Patients with prostate cancer scheduled for a diagnostic [18F]-DCFPyL PSMA PET scan as part of standard of care were eligible. Upon completion of the diagnostic PSMA PET scan, images were transferred to the radiotherapy planning system for target identification and contouring. If at least one PET avid tumor lesion was identified, the patient was then scanned on the X1 unit. BgRT planning was performed on each X1 scanned patient. The target lesion volume, activity concentration (AC) and normalized target signal (NTS) were acquired. Successful and deliverable BgRT plans required that the target AC was ≥ 5 kBq/ml and NTS ≥ 2.7.

RESULTS

Twenty-six patients underwent [18F]-DCFPyL PET scans (13 with rising PSA after surgery or radiotherapy, 6 with known metastases and 7 with newly diagnosed high-risk prostate cancer). Median (range) PSA was 3.40 (0.04-122). In 16 patients a PET avid tumor was identified and contoured for planning (4 lymph nodes, 5 bone, 6 prostate gland, and 1 prostate bed). In 13 patients the target lesion was visualized on the X1 PET scan, while in 3 patients the target lesion was too close to the bladder to be clearly visualized. BgRT planning was feasible and met standard of care published SBRT organ dose constraints in 8 patients (3 prostate gland, 3 bone, 2 lymph nodes). BgRT planning was not feasible in 8 patients due to insufficient AC, low NTS or proximity of the target lesion to the PET avid bladder. The accompanying table compares median (range) target volume, AC and NTS for feasible versus not feasible plans.

CONCLUSION

This is the first study to investigate the feasibility of using [18F]-DCFPyL PET imaging for BgRT plan generation on the X1 system in patients with prostate cancer. Lesions that are relevant to radiotherapy of prostate cancer can be visualized including lymph node and bone metastases. A dedicated BgRT workflow with PSMA PET imaging on the X1 at 60 minutes post injection will result in higher target AC and will optimize BgRT planning. PET avid lesions < 1 cm or close to the bladder may make BgRT planning challenging. [18F]-DCFPyL-guided BgRT is technically feasible using the RefleXion X1. BgRT using targeted PET radiopharmaceuticals to biologically guide external beam radiotherapy represents a promising new dimension in radiation oncology and warrants further investigation.

Bridging Radiotherapy Prior to Chimeric Antigen Receptor T-Cell Therapy for B-Cell Lymphomas: An ILROG Multi-Institutional Study

PURPOSE/OBJECTIVE(S)

To report an ILROG multi-institutional analysis of bridging radiotherapy (BRT) prior to CD19-targeting chimeric antigen receptor T-cell (CAR T) therapy for relapsed/refractory aggressive B-cell lymphomas (BCL).

MATERIALS/METHODS

Weretrospectively reviewed 115 patients (pts) with diffuse large BCL (n = 101, 88%), primary mediastinal BCL (n = 11, 10%), mantle cell lymphoma (n = 2, 2%), and T-cell/histiocyte rich large BCL (n = 1, 1%) who received BRT prior to commercial CAR T from 2018-2020 across 6 institutions. BRT toxicities were graded per CTCAE v5.0, cytokine release syndrome (CRS) per ASTCT, and immune effector cell-associated neurotoxicity syndrome (ICANS) per either ASTCT or CTCAE v5.0. Progression-free survival (PFS) and overall survival (OS), measured from CAR T infusion, were estimated using the Kaplan-Meier method. PFS was modeled using Cox regression with stepwise variable selection.

RESULTS

BRTwas given prior to axicabtagene ciloleucel (axi-cel; n = 82, 71%), tisagenlecleucel (tisa-cel; n = 31, 27%), or brexucabtagene autoleucel (n = 2, 2%). Median age was 62 years with median of two prior lines of therapy. Most pts had advanced stage III/IV disease at leukapheresis (n = 87, 76%), elevated pre-leukapheresis LDH (n = 73, 63%), and bulky disease (n = 55, 50%) (1 lesion ≥7.5 cm). 78 pts (68%) had extranodal disease, 12 (10%) had central nervous system (CNS) involvement, and 36 (31%) had bone involvement. Systemic bridging therapy was given to 42 pts (37%). Median intervals from leukapheresis to BRT start and from BRT completion to CAR T infusion were 5 days (IQR -6, 11) and 12 days (IQR 9, 23), respectively. BRT was delivered to 163 total sites; most commonly the abdomen/pelvis (n = 58, 50%), head/neck (n = 34, 30%), thorax (n = 20, 17%), extremity/soft tissue (n = 20, 17%), and CNS (n = 13, 11%). Median biologically effective dose was 31.3 Gy (IQR 24, 39). Most common regimen was 30 Gy in 10 fractions (n = 27, 17%). 40 pts (35%) received comprehensive BRT (to all active lesions). There were no grade ≥3 BRT toxicities. Grade ≥3 CRS occurred in 9 pts (8%), including 8/82 (10%) after axi-cel and 1/31 (3%) after tisa-cel. Grade ≥3 ICANS occurred in 23 pts (20%), including 22/82 (27%) after axi-cel and 1/31 (3%) after tisa-cel. Median follow up was 26.9 months. 1- and 2-year OS rates were 60% and 49%. 1- and 2-year PFS rates were 41% and 35%. Comprehensive BRT associated with superior PFS (HR 0.34, 95% CI 0.19-0.62, p<0.001) in a multivariable model with age ≥60, ECOG ≥2, advanced stage, CNS disease, pre-leukapheresis LDH, and axi-cel.

CONCLUSION

In this multi-institutional study, pts receiving BRT prior to CAR T therapy for BCL frequently had bulky disease yet experienced favorable PFS and OS. There were no serious toxicities attributable to BRT, and the rates of CRS and ICANS are comparable to those after CAR T alone. Comprehensive BRT associated with superior PFS.

Dosimetric Plan Evaluation of Biology Guided Radiotherapy Using [18F]-DCFPyL PSMA Radiotracer in Patients with Prostate Cancer

PURPOSE/OBJECTIVE(S)

The X1 system represents a cutting-edge solution in radiotherapy delivery, with its capability to perform Biology Guided Radiotherapy (BgRT). The system utilizes real-time positron emission tomography (PET) signal as biological fiducials to provide tracked dose delivery and is initially available for use with [18F]-Fluorodeoxyglucose (FDG). The aim of this research study is to assess the quality of BgRT treatment plans for prostate cancer using patients' PSMA PET images obtained on the X1 system.

MATERIALS/METHODS

Sixteen patients with at least one PET-avid tumor identified on their whole-body diagnostic PSMA PET scan were selected. These patients were scanned on X1 following their diagnostic scan without additional radiotracer administration. Based on the X1 PET images, a BgRT plan was created for each patient, with the prescription dose determined by the location of treatment sites. The planning objectives of organs-at-risk (OARs) were established in accordance with the 2018 Timmerman guidelines. Target coverage objective was the dose covering 95% (D95%) of the planning target volume (PTV) to be higher than 100%. The following parameters were analyzed: PTV D95%, the minimal dose (Dmin) of gross tumor volume (GTV), plan maximum dose (Dmax), conformity index (CI), gradient index (GI), and maximum point dose (D0.03cc) to the nearest OARs. The X1 BgRT planning system also generated dose volume histogram (DVH) bounds, which model variations in BgRT delivery. The low boundary of GTV Dmin, representing the minimum GTV dose in the worst-case scenario, was recorded.

RESULTS

BgRT plans were created for all patients, except for one where the target signal was indistinguishable from the bladder. The prescription dose was 2700 cGy or 3000 cGy in 3 fractions for lymph node lesions, 2400 cGy to 3000 cGy in 3 fractions for bone metastasis, and 4500 cGy in 5 fractions for lesions in prostate. All plans met the dose constraints for OARs as per the Timmerman guidelines. The Dmax of all plans was 129.9% ± 6.9% (mean ± standard deviation). The PTV D95% and GTV Dmin were 101.7% ± 1.0% and 111.0% ± 7.6%, respectively. The low boundary of GTV Dmin was 95.9% ± 5.8%. The CI and GI were 1.22 ± 0.11 and 9.40 ± 2.12, respectively. The D0.03cc to nearest OARs was 84.6% ± 25.4%. The estimated treatment time was 699 ± 228 seconds.

CONCLUSION

This study is a pioneering effort to evaluate the quality of BgRT plans for prostate cancer patients using the [18F]-DCFPyL PSMA radiotracer. Our results showed that all BgRT plans met the planning objectives defined in the Timmerman protocol. BgRT with [18F]-DCFPyL represents a promising treatment modality for patients with prostate cancer. Further research is needed to validate this approach, including a comprehensive assessment of the dosimetric and tracking accuracy through physical measurements.

First-in-Human Phase I Trial Combining Biologically Guided Radioimmunotherapy (RIT) Using a 90Y-Anti-CD25 Monoclonal Antibody (Mab) with CT-guided Total Marrow and Lymphoid Irradiation (TMLI) in Relapsed and Refractory (R/R) Acute Leukemia

PURPOSE/OBJECTIVE(S)

Patients with R/R acute leukemia after allogeneic hematopoietic cell transplant (alloHCT) have a dismal prognosis with 3-year survival rates of < 20%. To improve outcomes, innovative targeted forms of organ sparing radiotherapy, such as tumor-specific RIT and TMLI, are needed to dose escalate with acceptable toxicities, especially in patients ≥ age 60 years who cannot tolerate total body irradiation (TBI) / myeloablative regimens and who have a poor prognosis. CD25 is an ideal RIT target given its expression in acute leukemias, association with poor prognosis, and expression by leukemia stem cells. In this phase I trial (NCT05139004) we hypothesized that combining dose escalated 90Y-anti-CD25 RIT with fixed dose TMLI 12 Gy, fludarabine (flu), and melphalan (mel) in patients with R/R disease is safe and associated with acceptable toxicities.

MATERIALS/METHODS

The primary objective of this trial is to determine the maximum tolerated dose and recommended phase 2 dose of 90Y-anti-CD25 Mab (Day -15) with 12 Gy TMLI (1.5 Gy twice a day, days -8 to -5), flu (30 mg/m2/d days -5 to -2), and mel (100 mg/m2, day -2) in patients ≥ 60 years old or with a HCT-comorbidity index ≥ 2 and with R/R AML, ALL or myelodysplastic syndrome (MDS) scheduled to undergo alloHCT from a matched donor. TMLI mean organ dose constraints for kidney, lung and liver were 4 Gy. Planned dose levels of 90Y-anti-CD25 were 0.3, 0.4, and 0.5 mCi/kg. 111In-anti-CD25 (5 mCi) was co-infused followed by serial nuclear scans to assess dosimetry and biodistribution.

RESULTS

To date 5 patients (ages 31-74) with R/R AML have been treated. Marrow and circulating blasts ranged from 10-36% and 9-44%, respectively. For the 3 patients at 0.3 mCi/kg, follow-up ranged from 89-191+ days. 90Y/111In-anti-CD25 nuclear scans demonstrated persistent uptake in bone out to 144 hours, which was associated with a decline in circulating blasts. After combined RIT and TMLI, mean doses (Gy) to lungs ranged from 5.7-6.5, to kidneys from 7.5-8.2 and to liver from 7.2-11.6. No dose-limiting toxicities (DLT) were observed. All 3 patients achieved CR on day +30 bone marrow biopsies and 2 remained in CR on day +90 biopsies. Two patients have recently been treated at the 0.4 mCi/kg dose level. The results of patients treated at the higher dose levels will be provided.

CONCLUSION

Dose escalation by adding 90Y-anti-CD25 RIT at 0.3 mCi/kg to 12 Gy TMLI was safe, including in older patients, with no dose-limiting toxicities, mean critical organ doses lower than conventional myeloablative TBI, and encouraging response rates. The toxicity profile and dose estimates at 0.3 mCi/kg predict that the planned higher dose levels will also be feasible with acceptable toxicities. RIT and TMLI are complementary and when combined address the limitations of each modality. Combining these targeted therapies may be a superior strategy to intensify dose to leukemia compared to dose escalation of either modality alone.

Machine Learning and Explainable Artificial Intelligence to Predict Occult Pelvic Nodal Metastases in Prostate Cancer

PURPOSE/OBJECTIVE(S)

Determination of risk of occult pelvic lymph node involvement (LNI) in patients with cN0 prostate cancer is critical for determination of optimal treatment options. Though several nomograms exist, machine learning (ML) approaches might enable physicians to better assess individual risk by incorporating multiple clinical risk factors. Herein, we developed a ML model to predict occult LNI, and explained its composition using an explainable artificial intelligence (XAI) framework.

MATERIALS/METHODS

Patients with cN0 prostate adenocarcinoma diagnosed from 2018-2020 were identified in the National Cancer Database. The query was limited to patients with known clinical staging and biopsy results who did not receive neoadjuvant therapy prior to pelvic nodal examination. Occult LNI was defined as pN1 disease based on surgical evaluation, with a minimum of 10 nodes examined. Five ML models were trained to predict LNI. Variables incorporated into the model were age, core biopsy results, Gleason scores, preoperative prostate specific antigen (PSA), and clinical T-stage. Model performance, measured using area under the receiver operator characteristic curve (AUC) on a holdout testing dataset, was compared to multivariable logistic regression. The best-performing model was explained using SHapley Additive exPlanation (SHAP) values. To permit more clinically-meaningful statistical interpretation, using a novel approach SHAP values were converted into odds ratios (OR), confidence intervals (CI), and p-values.

RESULTS

A total of 23,131 patients met inclusion criteria; 2,676 (11.6%) had occult LNI. The Extreme Gradient Boosting model outperformed all other models with an AUC of 0.82 (95% CI: 0.78-0.86) compared to 0.80 (95% CI: 0.76-0.84) for logistic regression. Increasing PSA (OR: 1.031; p<0.001), number of positive biopsy cores (OR: 1.055; p<0.001), and percent positive biopsy cores (OR: 1.01; p<0.001) were all associated with increased risk of LNI. Based on observation of SHAP dependence plots, risk of LNI plateaued at PSA>20 ng/dL and >11 positive cores, while no plateau was observed for percent positive biopsy cores. Relative to T1c disease, patients with T3b were at highest risk of LNI (OR: 1.461; p = 0.003). Gleason score of 9 was associated with significant risk of LNI (Ref: Gleason 6; OR: 1.891; p<0.001). This was primarily driven by the primary Gleason score; primary Gleason 5 disease was associated with significant risk of LNI (Ref: Gleason 3; OR: 1.915; p<0.001) while a secondary Gleason score of 5 was the only grade with significant increased risk of LNI (Ref: Gleason 3; OR: 1.185; p = 0.004). Age and number of cores examined were not significant predictors of LNI.

CONCLUSION

Our ML achieved improved performance relative to logistic regression at predicting occult LNI. XAI provided insight into the inner-working of the ML model. ML can be used to identify patients at risk for occult LNI and therefore inform clinical decision-making.

Phase II Multi-Institutional Study of a Low-Dose (4 Gy) Palliative Response-Adapted Radiotherapy Regimen for Symptomatic Bone Metastases from Multiple Myeloma: Planned Interim Analysis of First 40 Patients

PURPOSE/OBJECTIVE(S)

Painful bone lesions are common in patients with multiple myeloma (MM). Radiotherapy (RT) is effective in providing pain relief from MM bone lesions in over 80% of patients. There is no consensus as to the most effective dose or fractionation for palliation. Shorter courses of therapy are not only more convenient for patients, but they also have less impact on timing of systemic therapies. There is precedent for using 4 Gy in the palliation of lymphomas, which have similar radiosensitivity to myeloma. The primary objective of this trial is to determine whether treatment with a total dose of 4 Gy to a painful myeloma bone lesion achieves patient-reported pain reduction comparable to historical controls at 4 weeks.

MATERIALS/METHODS

Patients with a known diagnosis of MM and a painful bone lesion that was not at the base of skull, in need of stabilization, or causing cord compression were treated with 4 Gy (2 Gy x 2 or 4 Gy x 1). Patients' pain was measured using the brief pain index (BPI) prior to treatment and at 2, 4, 8 weeks and 6 months following treatment. Pain response was determined by the international consensus on palliative radiotherapy and considered change in BPI and oral morphine equivalent dose (OMED). A planned interim analysis for futility was completed after 40 patients. Reirradiation with clinician choice regimens could be considered at ≥4 weeks following initial treatment for indeterminate pain response or pain progression.

RESULTS

Forty patients were treated at 6 institutions between 2019 and 2022. Median age was 65 years with 40% women and 88% with an ECOG of 0-1. A complete response (CR) was defined as a BPI score of 0 with no concomitant increase in OMED. A partial response (PR) was defined as BPI reduction in 2 or more without analgesic increase, or an OMED reduction of 25% or more without an increase in pain. An indeterminate response (IR) was any response that is not captured by a CR, PR or pain progression. A CR was achieved in 48%, a PR in 38% of patients, an IR in 13% with 1 patient who refused participation. Pain response was achieved in 86% of patients. Seven patients (18%) requested reirradiation at ≥4 weeks. Median BPI at baseline and 4 weeks after RT for patients with CR, PR, and IR were 3.75 and 0, 4.00 and 1, and 5.25 and 4.75, respectively. Median change of BPI between baseline and 4 weeks after RT for all responders (CR and PR) was -3.25. The median PTV volume (cc) for patients with CR, PR and IR were 81, 140 and 226, respectively. Based on these results, the futility threshold was not met, and the recommendation by the DSMC is to continue the trial.

CONCLUSION

In the first 40 patients who received 4 Gy palliation for painful bone lesions from multiple myeloma, there were 86% that had a pain response (48% CR, 38% PR). This low dose, response-adapted treatment, led to reirradiation in less than 20% of patients.

ACR-ARS Practice Parameter for the Performance of Total Body Irradiation

OBJECTIVES

This practice parameter was revised collaboratively by the American College of Radiology (ACR) and the American Radium Society (ARS). This practice parameter provides updated reference literature regarding both clinical-based conventional total body irradiation and evolving volumetric modulated total body irradiation.

METHODS

This practice parameter was developed according to the process described under the heading The Process for Developing ACR Practice Parameters and Technical Standards on the ACR website ( https://www.acr.org/Clinical-Resources/Practice-Parameters-and-Technical-Standards ) by the Committee on Practice Parameters-Radiation Oncology of the ACR Commission on Radiation Oncology in collaboration with the ARS.

RESULTS

This practice parameter provides a comprehensive update to the reference literature regarding conventional total body irradiation and modulated total body irradiation. Dependence on dose rate remains an active area of ongoing investigation in both the conventional setting (where instantaneous dose rate can be varied) and in more modern rotational techniques, in which average dose rate is the relevant variable. The role of imaging during patient setup and the role of inhomogeneity corrections due to computer-based treatment planning systems are included as evolving areas of clinical interest notably surrounding the overall dose inhomogeneity. There is increasing emphasis on the importance of evaluating mean lung dose as it relates to toxicity during high-dose total body irradiation regimens.

CONCLUSIONS

This practice parameter can be used as an effective tool in designing and evaluating a total body irradiation program that successfully incorporates the close interaction and coordination among the radiation oncologists, medical physicists, dosimetrists, nurses, and radiation therapists.

First-In-Human Pilot PET Immunoimaging Study of 64Cu-Anti-Carcinoembryonic Antigen Monoclonal Antibody (hT84.66-M5A) in Patients with Carcinoembryonic Antigen-Producing Cancers

Background: PET imaging using radiolabeled immunoconstructs shows promise in cancer detection and in assessing tumor response to therapies. The authors report the first-in-human pilot study evaluating M5A, a humanized anti-carcinoembryonic antigen (CEA) monoclonal antibody (mAb), radiolabeled with ⁶⁴Cu in patients with CEA-expressing malignancies. The purpose of this pilot study was to identify the preferred patient population for further evaluation of this agent in an expanded trial. Methods: Patients with CEA-expressing primary or metastatic cancer received ⁶⁴Cu-DOTA-hT84.66-M5A with imaging performed at 1 and 2 days postinfusion. ⁶⁴Cu-DOTA-hT84.66-M5A PET scan findings were correlated with CT, MRI, and/or FDG PET scans and with histopathologic findings from planned surgery or biopsy performed postscan. Results: Twenty patients received ⁶⁴Cu-DOTA-hT84.66-M5A. Twelve patients demonstrated positive images, which were confirmed in 10 patients as tumor by standard-of-care (SOC) imaging, biopsy, or surgical findings. Four of the 8 patients with negative imaging were confirmed as true negative, with the remaining 4 patients having disease demonstrated by SOC imaging or surgery. All 5 patients with locally advanced rectal cancer underwent planned biopsy or surgery after ⁶⁴Cu-DOTA-hT84.66-M5A imaging (4 patients imaged 6-8 weeks after completing neoadjuvant chemotherapy and radiation therapy) and demonstrated a high concordance between biopsy findings and ⁶⁴Cu-DOTA-hT84.66-M5A PET scan results. Three patients demonstrated positive uptake at the primary site later confirmed by biopsy and at surgery as residual disease. Two patients with negative scans each demonstrated complete pathologic response. In 5 patients with medullary thyroid cancer, ⁶⁴Cu-DOTA-hT84.66-M5A identified disease not seen on initial CT scans in 3 patients, later confirmed to be disease by subsequent surgery or MRI. Conclusions: ⁶⁴Cu-DOTA-hT84.66-M5A demonstrates promise in tumor detection, particularly in patients with locally advanced rectal cancer and medullary thyroid cancer. A successor trial in locally advanced rectal cancer has been initiated to further evaluate this agent's ability to define tumor extent before and assess disease response after neoadjuvant chemotherapy and radiotherapy. clinical trial.gov (NCT02293954).

Transcriptomic profiling identifies genomic markers associated with benefit from stereotactic body radiation therapy (SBRT) in oligoprogressive metastatic renal cell carcinoma (mRCC)

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Background: Addition of SBRT to systemic therapy in oligoprogressive mRCC has been shown to prolong the duration of systemic treatment (Cheung et al Eur Urol 2021; De et al BJUI 2021). To date, the genomic predictors of benefit are unknown. We hypothesized that hypoxia-related genes would be associated with lesser benefit from SBRT. Methods: We retrospectively identified patients (pts) with mRCC who had oligoprogressive disease (progression of < 5 sites) while on systemic treatment and received SBRT without any systemic treatment change or interruption. Clinicopathologic characteristics, whole exome and transcriptome sequencing (Ashion Analytics) data were collected. Duration of systemic therapy (DOT) was quantified as systemic treatment duration prior to oligoprogression (DOT[P]) and after completion of SBRT (DOT[S]). The ratio of DOT[S]/DOT[P] was calculated and patients with a ratio ≥ 1.0 were considered to derive greater benefit from SBRT. The frequency of specific DNA alterations and RNA expression of pts above and below a DOT[S]/DOT[P] threshold of 1.0 was compared using a two-tailed Fischer’s exact and student’s t-test, respectively. Results: In this study, 23 mRCC pts who had oligoprogression during systemic treatment and received SBRT were identified. Within this cohort 16 pts (69.6%; M:F, 12:4) had available genomic data. Median age was 70 years and the most common histology was clear cell (87.5%). At the time of oligoprogression 11 pts (68.8%) were on immunotherapy, 4 pts (25.0%) were on targeted therapy. Median DOT[S] and DOT[P] were 12.6 months (range,0.7-46.3) and 13.4 months (range, 0.5-26.9), respectively, with a median DOT[S]/DOT[P] ratio of 1.4 (range,0.01-3.8). The most commonly mutated genes were VHL (56.3%), PBRM1 (37.5%), and SETD2 (37.5%). Alterations in VHL, PBRM1 and SETD2 were seen in 66.7% vs 42.9%, 33.3% vs 43.9%, and 44.4% vs 28.6% in patients with greater vs lesser benefit from SBRT, respectively (p≥0.05for each). Transcriptomic analysis was available in 9 pts and 1580 genes were noted to be differentially expressed between the groups (p < 0.05). Limiting scope to cancer genes in the COSMIC database, pts with lesser benefit from SBRT had higher expression of CDKN1B, CNBP, and FOXO3 whereas pts with greater benefit had higher expression of RNF43, POLD1 and PBRM1 (p < 0.05 for each). Gene set enrichment analysis showed a trend towards increased expression of hypoxia related genes in pts with lesser benefit. Conclusions: Our data align with existing studies supporting the role of SBRT in oligoprogressive mRCC. In addition, while clinical benefit from SBRT appears to be independent of DNA-level alterations, transcriptomic analysis revealed significant differences in gene expression. Hypoxia-associated signatures may be associated with lesser benefit from radiotherapy.

Prolonging utilization of systemic therapy in oligoprogressive metastatic renal cell carcinoma using stereotactic body radiation therapy

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Background: SBRT in indicated for the management of locally recurrent and oligometastatic mRCC as per National Comprehensive Cancer Network guidelines. Our study evaluates both the efficacy of radiotherapy (RT) in prolonging systemic treatment along with RT toxicity in the oligoprogressive RCC setting. Methods: A single institution retrospective data collection was performed in which we identified mRCC patients who experienced oligoprogression (defined as <1 sites of progressive disease) while on an FDA approved systemic therapy and were concurrently treated with SBRT, while remaining on the same therapy. Clinicopathologic characteristics and SBRT-related data along with duration of systemic therapy (DOT) were collected. DOT was then quantified into two categories which included the duration of systemic therapy prior to oligoprogression (DOT[P]) and duration of systemic therapy after completion of SBRT (DOT[S]). The ratio of DOT[S]/DOT[P] was calculated to determine the impact of SBRT on systemic treatment prolongation. Results: 23 patients diagnosed with mRCC meeting criteria were identified, 91% (n = 21) with clear cell histology and 9% (n = 2) with papillary histology. At the time of oligoprogression, 15 patients (65%) were on immunotherapy, 7 patients (30%) were on targeted therapy, and 1 patient (5%) was on combination therapy. We noted the preponderance of patients were on a first-line therapy at the time of oligoprogression (n = 10, 43%). A median of 2 (range, 1-3) lesions were treated per patient, with lung being the most frequent site (n = 14, 40%). The median total dose of SBRT was 30 Gy (range, 27-50 Gy) with a median dose per fraction of 6 Gy (range, 3-12 Gy). SBRT related toxicities, all of which were grade <2, were noted in 5 patients (22%), of which fatigue was the most frequent side effect (n = 3, 13%). Median DOT[S] was 13.4 months (range, 0.5-37.7 months) and the median DOT[P] was 12.8 months (range, 0.4-46.3 months). Results demonstrated a median DOT[S]/DOT[P] ratio to be 1.3 (range, 0.01-25.8). Conclusions: Based on our data, we discovered the addition of SBRT to systemic therapy during oligoprogression is not only well-tolerated, but that this treatment had clinical benefit in prolonging time on systemic therapy for patients with mRCC. The utilization of SBRT may prolong lines of therapy, thereby decreasing additional toxicities associated with exposure to new regimens.

Brentuximab Vedotin Combined With Chemotherapy in Patients With Newly Diagnosed Early-Stage, Unfavorable-Risk Hodgkin Lymphoma

PURPOSE

To improve curability and limit long-term adverse effects for newly diagnosed early-stage (ES), unfavorable-risk Hodgkin lymphoma.

METHODS

In this multicenter study with four sequential cohorts, patients received four cycles of brentuximab vedotin (BV) and doxorubicin, vinblastine, and dacarbazine (AVD). If positron emission tomography (PET)-4-negative, patients received 30-Gy involved-site radiotherapy in cohort 1, 20-Gy involved-site radiotherapy in cohort 2, 30-Gy consolidation-volume radiotherapy in cohort 3, and no radiotherapy in cohort 4. Eligible patients had ES, unfavorable-risk disease. Bulk disease defined by Memorial Sloan Kettering criteria (> 7 cm in maximal transverse or coronal diameter on computed tomography) was not required for cohorts 1 and 2 but was for cohorts 3 and 4. The primary end point was to evaluate safety for cohort 1 and to evaluate complete response rate by PET for cohorts 2-4.

RESULTS

Of the 117 patients enrolled, 116 completed chemotherapy, with the median age of 32 years: 50% men, 98% stage II, 86% Memorial Sloan Kettering-defined disease bulk, 27% traditional bulk (> 10 cm), 52% elevated erythrocyte sedimentation rate, 21% extranodal involvement, and 56% > 2 involved lymph node sites. The complete response rate in cohorts 1-4 was 93%, 100%, 93%, and 97%, respectively. With median follow-up of 3.8 years (5.9, 4.5, 2.5, and 2.2 years for cohorts 1-4), the overall 2-year progression-free and overall survival were 94% and 99%, respectively. In cohorts 1-4, the 2-year progression-free survival was 93%, 97%, 90%, and 97%, respectively. Adverse events included neutropenia (44%), febrile neutropenia (8%), and peripheral neuropathy (54%), which was largely reversible.

CONCLUSION

BV + AVD × four cycles is a highly active and well-tolerated treatment program for ES, unfavorable-risk Hodgkin lymphoma, including bulky disease. The efficacy of BV + AVD supports the safe reduction or elimination of consolidative radiation among PET-4-negative patients.

Review of Radium-223 and Metastatic Castration-Sensitive Prostate Cancer

Background: Radium-223 is approved for treatment of bone metastases in metastatic castration-resistant prostate cancer (mCRPC). After the ALSYMPCA trial showed overall survival benefit with the addition of radium-223 to standard of care in mCRPC in 2013, there have been numerous publications and trials using radium-223 in mCRPC. Recently, there has been interest in using radium-223 earlier in the metastatic prostate cancer timeline, in metastatic castrate-sensitive prostate cancer (mCSPC); however, currently, radium-223 in mCSPC treatment is investigational. Aim: A literature search was conducted to review the use of radium-223 in mCSPC treatment from 1980 to 2019. A review of both radium-223 articles and abstracts was performed. Search terms included metastatic prostate cancer and radium-223, mCSPC, hormone-sensitive metastatic prostate cancer, radium-223, and oligometastatic disease. The results were limited to studies involving multiple patients with mCSPC. Conclusion: There are a limited number of studies of radium-223 in mCSPC treatment and the authors report on these studies (two published studies and four ongoing trials). Trials are currently underway to assess if radium-223 could be used in mCSPC as a treatment for bone metastases and micrometastases. Future data from these trials will be informative as to the benefit of radium-223 in mCSPC treatment and may change treatment paradigms for mCSPC. This review will focus on trials assessing the role of radium-223 in mCSPC.

Management of the primary site in stage IV non-small cell lung cancer: SEER analysis

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Background: One of every three non-small cell lung cancer (NSCLC) patients is diagnosed with terminal stage IV disease. As systemic treatments have evolved, other tumor sites such as kidney have demonstrated benefits of aggressive management of the primary location and oligo-metastases. The purpose of this study is to use the SEER database to evaluate survival outcomes associated with surgery (S) and radiation treatment (RT) of the primary site in stage IV NSCLC. Methods: Eligible patient cases had lung coded as the primary location. The analysis was limited to histology of squamous cell carcinoma or adenocarcinoma, M1 staging, had recorded extent of surgery and status of radiation, were taken from years 1998-2013 and grouped from 1998-00, 01-05, 06-10, 11-2013 for temporal analysis. Kaplan-Meier was used to estimate median overall survival (MOS) and lung cancer specific survival (CSS). Results: There were 41150 patients meeting inclusion criteria with median follow up of 4 months limited by survival. Treatment was S only to 494, RT only to 20346, S+RT to 731 and neither to 19579. Of the dual modality patients, 85 had RT before S, 525 after and 121 unknown order. Node negative surgical patients undergoing lobectomy had better median OS & CSS (30 & 35 m respectively) than all other surgical categories (eg. wedge resection with 13 & 17m, pneumonectomy with 10 & 15m). Median OS & CSS decreased slightly from 5 to 3 and 6 to 4 months over the time from 2000-2013. In the subset with N0 disease, those receiving both S+RT observed an increase of median OS & SS from 11 to greater than 35 months (median not reached in 2013) while no trend was seen for other treatment strategies, which were ~5 months in 2013. Conclusions: Potential sources of confounding and bias must be regarding when interpreting our findings. These include selection of patient for aggressive treatment, both local and systemic, the latter of which this database does not describe. Our findings demonstrate that, in stage IV NSCLC, aggressive management of the primary site with surgery and radiation in patients with limited local disease such as N0 lymph nodes is associated with prolonged survival.

Impact of radiation and surgery for intraductal papillary neoplasm of the bile duct: A population-based analysis

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Background: Intraductal Papillary Neoplasm of the Bile Duct (IPNB), either in-situ or invasive, is a histological variant with better prognosis then the more common adenocarcinoma. This study’s purpose is to use the Surveillance Epidemiology and End Results (SEER) database to evaluate prognostic factors: histology, stage, location, extent of surgery and the use of radiation therapy (RT). Methods: Cases from 1973-2011 were acquired. Inclusion criteria included intrahepatic (IHD), extrahepatic bile duct (EHD) or ampulla of vater (AoV) locations, first primary, extent of surgery and RT history. Kaplan-Meier and Log-Rank methods measured overall survival (OS) and disease specific survival (DSS) in months (m) and their medians (MOS, MDSS). Cox multivariate regression computed hazard ratios (HR) controlling for stage, treatment, surgical extent and histology. Results: . For non-invasive cases, 14% were IPNB (n = 31). Survival was similar for EHD & AoV cases. Surgery was associated with prolonged MOS of 120m compared to 8m without surgery or RT. A trend suggested better survival with lesser extent of surgery for EHD & AoV cases (p < 0.16, n = 8 at both sites). For invasive cases, 5% were IPNB (n = 1309). For cases not receiving surgery, RT was associated with prolonged OS & DSS from 3 to 7m (p = 0.026) and 4 to 8m (p = 0.074). In T1N0M0 EHD cases, surgery with and without RT had similar OS & DSS. Cox analysis observed similar OS & DSS for surgery with and without RT for EHD and AoV cases. Mucin-producing IPNB was less likely local stage disease (10% vs 39%, p < 0.01), with shorter OS 5m vs 23 m (p < 0.01) and DSS 6m vs 28m (p < 0.01), and for EHD cases, with HR = 2.0 (p < 0.01) compared to papillary type IPNB. Conclusions: For non-invasive IPNB, surgery with less extensive resections was associated with better prognosis. For invasive IPNB cases not amenable to surgery, RT improved short term survival. If high-risk factors such as suboptimal surgical margins, which are not recorded in SEER, correlated with the use of RT, then the outcomes in EHD & AoV locations could be explained by an imparted benefit. As well, mucin-associated IPNB, was associated with worse survival than papillary type. Further work is necessary to validate these findings.

Outcomes of medium choroidal melanomas treated with ruthenium brachytherapy guided by three-dimensional pretreatment modeling

PURPOSE

The Collaborative Ocular Melanoma Study (COMS) established iodine-125 (I-125) plaque brachytherapy for eye preserving treatment of medium-sized choroidal melanomas in the United States. Eye Physics I-125 plaque treatment modeled with Plaque Simulator (PS) software yields similar results to COMS. Herein, we report results from a series of 15 patients treated with ruthenium-106 (Ru-106) plaque brachytherapy using PS pretreatment modeling for plaque localization and dosimetry.

METHODS AND MATERIALS

Fifteen patients with medium-sized choroidal melanomas (2.84-5.5 mm in apical height and a basal diameter of 7.8-12.6 mm) treated with ruthenium brachytherapy from 2003 to 2005 were evaluated retrospectively. Baseline and followup data were evaluated for tumor height, best corrected visual acuity, radiation retinopathy, radiation optic neuropathy, postradiation cataract formation, diplopia, and ptosis. Tumor response for both Ru-106 and I-125 plaques planned using the same PS pretreatment modeling was evaluated and compared.

RESULTS

Isotope-specific radiation profiles were compared, and rates of local treatment failure (0%), optic neuropathy (6.7%), retinopathy (20%), and cataracts (33%) were evaluated. Five year-treated tumor heights were approximately 0.61 ± 0.29 (I-125, n = 16) and 0.53 ± 0.17 (Ru-106, n = 6) of their heights at diagnosis.

CONCLUSIONS

This patient subset had background characteristics very similar to those of the COMS and patients treated at our institution with I-125 plaques. Treatment response was equivalent although radiation complications occurred slightly less frequently in the Ru-106 group compared with those treated with I-125. Image-guided three-dimensional pretreatment modeling for plaque localization and dosimetry seems to work equally as well for Ru as for I-125 plaques and justifies more extensive investigation.

HIV- positive anal cancer: an update for the clinician

Anal cancer used to be a rare cancer traditionally associated with elderly women. There are approximately 5260 cases per year in the U.S. (1). The onslaught of the Human Immunodeficiency Virus (HIV) virus has led to a change in anal cancer demographics. Anal cancer is on the rise in the U.S and the number of anal cases documented has quadrupled in the past 20 yrs correlating with the rise of the HIV epidemic. The incidence of anal cancer is 40 to 80 fold higher in the HIV positive (HIV+) population when compared to the general population (2). With the advent of highly active antiretroviral therapy (HAART), HIV+ patients are living longer as less are progressing to AIDS. As a consequence non AIDS defining cancers such as anal cancer are on the rise. Factors implicated in the etiology of anal cancer in HIV+ patients include (Human papillomavirus) HPV virus status, sexual habits, and a history of smoking. HPV 16 and receptive anal intercourse (RAI) increase the risk of anal cancer by 33% over the general population. In the general population, the rate of anal cancer is approximately 0.9 cases per 100,000. In patients with a history of RAI, the rate approaches 35 cases per 100,000 which is equivalent to the prevalence of cervical cancer (3). Smokers are eight times more likely to develop anal cancer. There has been much discussion about tailoring treatment decisions in HIV+ patients with anal cancer. This review focuses on squamous cell carcinomas of the anal canal which comprise 80 to 90% of all anal cancers diagnosed and highlight key issues in the management of HIV+ anal cancer patients including recent clinical trials.

Evaluation of the SCA instrument for measuring patient satisfaction with cancer care administered via paper or via the Internet

Background: Patients’ perspectives provide valuable information on quality of care. This study evaluates the feasibility and validity of Internet administration of Service Satisfaction Scale for Cancer Care (SCA) to assess patient satisfaction with outcome, practitioner manner/skill, information, and waiting/access.

Patients and methods: Primary data collected from November 2007 to April 2008. Patients receiving cancer care within 1 year were recruited from oncology, surgery, and radiation clinics at a tertiary care hospital. An Internet-based version of the 16-item SCA was developed. Participants were randomised to Internet SCA followed by paper SCA 2 weeks later or vice versa. Seven-point Likert scale responses were converted to a 0–100 scale (minimum–maximum satisfaction). Response distribution, Cronbach’s alpha, and test–retest correlations were calculated.

Results: Among 122 consenting participants, 78 responded to initial SCA. Mean satisfaction scores for paper/Internet were 91/90 (outcome), 95/94 (practitioner manner/skill), 89/90 (information), and 86/86 (waiting/access). Response rate and item missingness were similar for Internet and paper. Except for practitioner manner/skill, test–retest correlations were robust r = 0.77 (outcome), 0.74 (information), and 0.75 (waiting/access) (all P < 0.001).

Conclusions: Internet SCA administration is a feasible and a valid measurement of cancer care satisfaction for a wide range of cancer diagnoses, treatment modalities, and clinic settings.

Measuring health-related quality of life consequences from primary treatment for early-stage prostate cancer

Radical prostatectomy, external radiation therapy, and brachytherapy are all mainstay treatment options for clinically localized prostate cancer. Over time, each of these treatments has been modified so as to maximize percent cancer-free survival while minimizing health-related risks such as urinary incontinence, bowel incontinence, and sexual dysfunction. With these efforts, there is still not one superior single treatment that is devoid of side effects. Concurrently, efforts have been made to generate validated health-related quality of life (HRQOL) measurement scales to aid in the decision making by both physician and patient. HRQOL measurement scales enable physicians to have informed discussions with patients about potential likelihood of a given set of side effects with the various prostate cancer treatment options. This review will highlight prostate cancer HRQOL outcomes and delineate further areas of study necessary to optimize evidence-based decision making for prostate cancer patients.

Mice with altered alpha-actinin-4 expression have distinct morphologic patterns of glomerular disease

Mutations in ACTN4, encoding the actin-binding protein alpha-actinin-4, cause a form of familial focal segmental glomerulosclerosis. We had developed two strains of transgenic mice with distinct alterations in the expression of alpha-actinin-4. One strain carried a human disease-associated mutation in murine Actn4, whereas the other knockout strain did not express alpha-actinin-4 protein. Most adult homozygous Actn4 mutant and knockout mice developed collapsing glomerulopathy. Homozygous Actn4 mutant mice also exhibited actin and alpha-actinin-4-containing electron-dense cytoplasmic structures, that were present but less prominent in heterozygous Actn4 mutant mice and not consistently seen in wild-type or knockout mice. Heterozygous Actn4 mutant mice did not develop glomerulosclerosis, but did exhibit focal glomerular hypertrophy and mild glomerular ultrastructural changes. The ultrastructural abnormalities seen in heterozygous Actn4 mutant mice suggest low-level glomerular damage, which may increase susceptibility to injury caused by genetic or environmental stressors. Our studies show that different genetic defects in the same protein produce a spectrum of glomerular morphologic lesions depending on the specific combination of normal and/or defective alleles.

Functional genetic variation in aminopeptidase A (ENPEP): lack of clear association with focal and segmental glomerulosclerosis (FSGS)

The aminopeptidase A (APA) ectopeptidase is an integral membrane-bound zinc metalloprotease that cleaves aspartic and glutamic acidic residues from the N-terminus of a number of protein substrates that includes angiotensin II. Angiotensin II, the most vasoactive component of the renin-angiotensin-aldosterone (RAAS) pathway, can contribute to renal disease by causing an increase in arterial blood pressure leading to glomerular injury and fibrosis. APA is expressed in many organs, including the kidney where it localizes mainly to the podocyte cell membrane and brush borders of the proximal tubule cells. Antibodies directed to the APA peptide can induce an acute massive albuminuria in wild-type BALB/c mice after intravenous injection. We examined whether variants in the APA encoding gene (ENPEP) are more frequent in individuals with the proteinuric disease focal and segmental glomerulosclerosis (FSGS) compared to control individuals. The ENPEP coding sequence was re-sequenced in 188 FSGS patients and 48 controls. Genetic variants were further genotyped in 181 individuals without any known kidney disease. We then examined the effect of the non-synonymous coding variants identified on their cell surface APA activity after transfection in COS-1 cells. Several of these ENPEP variants lead to reproducibly altered APA activity. However, we did not see a clear correlation between the presence of a functional ENPEP variant and FSGS. However, the existence of these variants with marked effect on APA activity suggests that both rare and common variation in ENPEP may contribute to the development of renal and hypertensive disorders and warrants further study.

α-Actinin-4 Is Required for Normal Podocyte Adhesion

Mutations in the alpha-actinin-4 gene ACTN4 cause an autosomal dominant human kidney disease. Mice deficient in alpha-actinin-4 develop a recessive phenotype characterized by kidney failure, proteinuria, glomerulosclerosis, and retraction of glomerular podocyte foot processes. However, the mechanism by which alpha-actinin-4 deficiency leads to glomerular disease has not been defined. Here, we examined the effect of alpha-actinin-4 deficiency on the adhesive properties of podocytes in vivo and in a cell culture system. In alpha-actinin-4-deficient mice, we observed a decrease in the number of podocytes per glomerulus compared with wild-type mice as well as the presence of podocyte markers in the urine. Podocyte cell lines generated from alpha-actinin-4-deficient mice were less adherent than wild-type cells to glomerular basement membrane (GBM) components collagen IV and laminin 10 and 11. We also observed markedly reduced adhesion of alpha-actinin-4-deficient podocytes under increasing shear stresses. This adhesion deficit was restored by transfecting cells with alpha-actinin-4-GFP. We tested the strength of the integrin receptor-mediated linkages to the cytoskeleton by applying force to microbeads bound to integrin using magnetic pulling cytometry. Beads bound to alpha-actinin-4-deficient podocytes showed greater displacement in response to an applied force than those bound to wild-type cells. Consistent with integrin-dependent alpha-actinin-4-mediated adhesion, phosphorylation of beta1-integrins on alpha-actinin-4-deficient podocytes is reduced. We rescued the phosphorylation deficit by transfecting alpha-actinin-4 into alpha-actinin-4-deficient podocytes. These results suggest that alpha-actinin-4 interacts with integrins and strengthens the podocyte-GBM interaction thereby stabilizing glomerular architecture and preventing disease.

The glomerular filter: Biologic and genetic complexity

The list of known genes that, when altered, cause proteinuric renal disease continues to increase. Recent mouse and human genetic studies, including that by Hasselbacher et al., are refocusing our attention on glomerular basement membrane components as critical to the barrier to protein filtration.