Positive Predictive Value of PET CT in HPV Associated Oropharyngeal Cancers Treated with Definitive Proton Therapy

PURPOSE/OBJECTIVE(S)

Proton therapy (PT) offers attractive dosimetric advantages but there is emerging literature suggesting relative biological effectiveness (RBE) differences at the distal end of the Bragg peak may result in increased posttreatment FDG avidity. While the utility of PET CT is well established, lingering posttreatment inflammation from PT may affect the interpretation of posttreatment scans (PTS). We seek to characterize the positive predictive value (PPV) and negative predictive value (NPV) for residual disease/locoregional recurrence in patients undergoing definitive PT with HPV associated oropharyngeal cancer.

MATERIALS/METHODS

We performed a single institution retrospective analysis of patients with HPV associated oropharyngeal cancer treated with PT between 2016-2022. Patients were included if they had both pretreatment and initial posttreatment restaging PET/CT available for analysis. SUVmax was recorded in both the primary tumor and involved lymph nodes. Patients were considered to have a positive PET CT if there was an SUV decrease of less than 65% from the baseline exam or if there was SUV > 4.0 based on thresholds defined by previous studies. Chi-square analysis was used to compare patients who had a positive PTS to those who did not.

RESULTS

Sixty-two patients were included for analysis with a median age of 62. The entire cohort had a median follow up of 21 months (Range 2-71 months) of whom 86% received chemotherapy. Eleven patients (17%) had PTS defined as positive, of whom only one (PPV 9%) was found to have residual/locoregionally recurrent disease within an area of FDG avidity on PTS. Another patient developed a new primary tumor 9 months later in an area outside of FDG avidity on PTS. The remainder were followed with serial clinical exam with or without the compliment of repeat imaging. They remained without evidence of residual/locoregionally recurrent disease at the time of last follow up. Fifty-one patients had negative posttreatment scans, with only one patient having residual/locoregionally recurrent disease (NPV 98%). On Chi-square analysis T1-2 vs T3-4 tumor, use of CTV margin vs no margin, chemotherapy vs no chemotherapy, smoking history, and tonsil vs base of tongue subsite were not statistically significant in association with positive PTS.

CONCLUSION

PET/CT for post-treatment evaluation of patients treated with PT had an expectedly high NPV of 98% for residual/locoregionally recurrent disease; however, the PPV was 9% (1/11) which is much lower than would be expected with photon-based treatment. These findings may be the result of lingering acute inflammation caused by RBE differences at the distal end of the Bragg peak. Our findings are hypothesis generating and require validation with larger well-matched patient cohorts.

Post-treatment PET/CT for p16-positive oropharynx cancer treated with definitive proton therapy

Objectives

Given emerging data suggesting that uncertainty in the relative biologic effectiveness at the distal end of the Bragg peak results in increased mucosal injury in patients with oropharynx cancer receiving adjuvant proton therapy, we evaluated the results of post-treatment positron emission tomography-computed tomography (PET/CT) in patients with p16-positive oropharynx cancer (p16+OPC) treated with definitive intensity-modulated proton therapy (IMPT).

Material and Methods

A retrospective cohort study of patients with p16+OPC treated with definitive IMPT between 2016 and 2022 was performed at a single institution. Patients with PET/CT scans within 6 months following completion of IMPT were included in the study. Positive post-treatment scans were defined by a maximum standard uptake values (SUVmax) >4.0 or a <65% reduction in SUVmax in either the primary tumor or lymph node. The Fisher's exact test was used to evaluate factors associated with positive post-treatment PET/ CT values.

Results

Sixty-two patients were included for analysis. Median follow-up was 21 months (range: 3-71 months) with a median time to post-treatment PET/CT of 3 months (range: 2-6 months). Median post-treatment SUVmax of the primary disease and nodal disease was 0 (mean: 0.8, range: 0-7.7) and 0 (mean: 0.7, range: 0-9.5), respectively. Median post-treatment percent reduction in SUVmax for the primary site and lymph node was 100% (mean: 94%, range: 31.3-100%) and 100% (mean: 89%, range: 23-100%), respectively. Eleven patients had a positive post-treatment PET/CT with one biopsy-proven recurrence. Negative and positive predictive values (NPV and PPV) were 98% and 9.1%, respectively. There were no factors associated with positive post-treatment PET/CT.

Conclusion

Similar to patients treated with photon-based radiation therapy, post-treatment PET/CT has a high NPV for patients with p16+OPC treated with definitive proton therapy and should be used to guide patient management. Additional patients and more events are needed to confirm the PPV of a post-treatment PET/CT in this favorable patient cohort.

Gross tumor volume margin and local control in p16-positive oropharynx cancer patients treated with intensity modulated proton therapy

BACKGROUND

To determine if the extent of high-dose gross tumor volume (GTV) to clinical target volume (CTV) expansion is associated with local control in patients with p16-positive oropharynx cancer (p16+ OPC) treated with definitive intensity modulated proton therapy (IMPT).

METHODS

We performed a retrospective analysis of patients with p16+ OPC treated with IMPT at a single institution between 2016 and 2021. Patients with a pre-treatment PET-CT and restaging PET-CT within 4 months following completion of IMPT were analyzed.

RESULTS

Sixty patients were included for analysis with a median follow-up of 17 months. The median GTV to CTV expansion was 5 mm (IQR: 2 mm). Thirty-three percent of patients (20 of 60) did not have a GTV to CTV expansion. There was one local failure within the expansion group (3%).

CONCLUSION

Excellent local control was achieved using IMPT for p16+ OPC independent of GTV expansion. IMPT with minimal target expansions represent a potential harm-minimization technique for p16-positive oropharynx cancer.

Abstract TP196: Real Life Utility Of PCSK9 Inhibitors Following Ischemic Stroke

Introduction: Hyperlipidemia is a modifiable risk factor for stroke, with the magnitude of LDL-C reduction correlating to risk of recurrent ischemic stroke. A high-intensity statin is considered standard of care in addition to dietary modification. Proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors are used if the LDL-C target is not achieved despite maximally tolerated statins with ezetimibe. We investigated the role for PCSK9 inhibitors in our ischemic stroke population.

Methods: An IRB approved retrospective review of patients admitted for acute ischemic stroke between 2019 – 2020 was performed. We estimated the probability of benefit from PCSK9 treatment with the following criteria: LDL > 190 regardless of treatment, LDL 161-190 on any dose statin therapy, and LDL 131-160 on high intensity statin therapy.

Results: 774 patients with ischemic stroke were admitted during this time frame. Mean age 62.8 +/- 13.2 with 57% male (52% Black, 42% White). 584 (75%) of these patients had LDL above goal. One patient was on PCSK9 therapy on admission. Although the majority of our patients had uncontrolled cholesterol, only one additional patient would meet the strict prescription criteria for PCSK9 therapy of being adherent to maximal tolerated statin dose and ezetimibe with LDL above goal. Other potential patients with estimated benefit include LDL >190 (20 patients), LDL 161-190 (16 patients), LDL 131-160 (13 patients). In total this amounts to 6.7% of stroke patients who we would expect to need PCSK9 inhibitors in the future.

Conclusion: Using conservative projections, we estimate that about 1 in 14 patients with ischemic stroke could benefit from PCSK9 therapy. Achieving LDL targets more consistently is a promising approach to decreasing the recurrent stroke rate. Further prospective data evaluating outcomes after initiating PCSK9 inhibitor treatment are needed to validate these findings.

Bedside angiography of distal perfusion catheter for veno-arterial extracorporeal membrane oxygenation

BACKGROUND

The aim of this study was to evaluate the ipsilateral lower extremity (ILE) outcomes of patients who underwent bedside angiography via the distal perfusion catheter while on femoral veno-arterial extracorporeal membrane oxygenation (VA ECMO).

METHODS

This is a retrospective analysis of all patients placed on VA ECMO at a single center from January 2017 to December 2019 who underwent bedside angiography via the distal perfusion catheter.

RESULTS

Twenty-four patients underwent bedside angiography via the distal perfusion catheter after being placed on VA ECMO. A vasodilator was directly administered in three patients for suspected spasm. One patient had distal thrombus and underwent thrombectomy and fasciotomy. One patient had a dislodged catheter and underwent thrombectomy, fasciotomy, and replacement of the catheter. One patient had severe ILE ischemia, however was not intervened upon due to critical acuity. Finally, one patient had inadvertent placement in the saphenous vein and had a new catheter placed in the SFA. No patients underwent amputation. Ultimately, 21 patients (87.5%) had no ILE compromise at the end their ECMO course. Survival to decannulation was 66.7% (n = 16).

CONCLUSIONS

Bedside angiography of the distal perfusion catheter is feasible and can be a useful adjunct in informing the need for further intervention to the ILE.

CLASSIFICATIONS

extracorporeal membrane oxygenation, ischemia.

Mesothelin Enhances Tumor Vascularity in Newly Forming Pancreatic Peritoneal Metastases

Over 90% of pancreatic ductal adenocarcinomas (PDAC) express mesothelin (MSLN). Overexpression or knockdown of MSLN has been implicated in PDAC aggressiveness. This activity has been ascribed to MSLN-induced activation of MAPK or NF-κB signaling pathways and to interaction of MSLN with its only known binding partner, MUC16. Here, we used CRISPR/Cas9 gene editing to delete MSLN from PDAC, then restored expression of wild-type (WT) or Y318A mutant MSLN by viral transduction. We found that MSLN KO cells grew in culture and as subcutaneous tumors in mouse xenografts at the same rate as WT cells but formed intraperitoneal metastases poorly. Complementation with WT MSLN restored intraperitoneal growth, whereas complementation with Y318A mutant MSLN, which does not bind MUC16, was ineffective at enhancing growth in both MUC16(+) and MUC16(-) models. Restoration of WT MSLN did enhance growth but did not affect cell-to-cell binding, cell viability in suspension or signaling pathways previously identified as contributing to the protumorigenic effect of MSLN. RNA deep sequencing of tumor cells identified no changes in transcriptional profile that could explain the observed phenotype. Furthermore, no histologic changes in tumor cell proliferation or morphology were observed in mature tumors. Examination of nascent MSLN KO tumors revealed decreased microvascular density as intraperitoneal tumors were forming, followed by decreased proliferation, which resolved by 2 weeks postimplantation. These data support a model whereby MSLN expression by tumor cells contributes to metastatic colonization. IMPLICATIONS: MSLN confers a growth advantage to tumor cells during colonization of peritoneal metastasis. Therapeutic blockade of MSLN might limit peritoneal spread.

Abstract 3767: Characterization of the protumorigenic role of MSLN in peritoneal metastases in pancreatic cancer

Peritoneal metastases develop in 70-80% of nonresectable patients with pancreatic cancer, and the onset of clinically significant ascites is associated with rapid demise. Mesothelin (MSLN) is a GPI-linked cell-surface glycoprotein expressed in &gt;90% of pancreatic ductal adenocarcinomas (PDAC) but not in healthy pancreas nor in the parenchyma of other vital organs. Due to this differential expression, multiple therapeutics targeting MSLN have already reached clinic. Overexpression of MSLN has been implicated in increased aggressiveness of PDAC, both in laboratory models and in patients. Here, we have used CRISPR-Cas9 gene editing to delete MSLN from the KLM-1 pancreatic cancer cell line (MSLN KO) and have examined the growth of these cells in culture and in nude mice compared to mock deleted cells (WT). The cells were also transduced to express GFP/Luciferase(Luc) in order to allow for monitoring of tumor by bioluminescence imaging (BLI) in the mouse intraperitoneal (IP) cavity. MSLN KO and WT cells grew at the same rate in culture and as subcutaneous xenografts in nude mice. But when cells were inoculated IP, KO cells grew poorly compared to WT cells or did not grow at all. When MSLN KO cells grew, visible tumors were located primarily at the inoculation site. In contrast, WT cells grew extensive metastases throughout the IP cavity. GFP/Luc+ tumor cells adhered to the mesothelial lining of the peritoneum could be detected by BLI and histology as early as 24h post IP injections. By 72h, the MSLN KO tumors had significantly decreased microvascular density as determined by CD31 staining, lower metastatic dissemination and growth as detected by BLI and H&E staining, and decreased proliferation as determined by Ki67 quantification. These differences were maintained even at timepoints out to 2 weeks. Our results suggest that MSLN might enhance peritoneal carcinomatosis of PDAC by positively regulating vascular remodeling/angiogenesis and tumor cell proliferation within the IP cavity. The mechanism of MSLN action has been previously ascribed to activation of MAPK or NF-kB pathways or signaling through MUC16, the only known binding partner of MSLN. However, we found no changes in phosphorylated p38 or ERK, nor in total levels of the NF-kB target OCT-2 upon KO of MSLN expression. Since we also observed protumorigenic effect of MSLN in a MUC16 deficient pancreatic cancer cell line, it is unlikely that MUC16 is responsible for the protumorigenic activity of MSLN. We are currently performing comprehensive molecular studies to uncover key upstream and downstream signaling factors responsible for the protumorigenic effects of MSLN in peritoneal dissemination.

Citation Format: Leela Rani Avula, Michael Rudloff, Salma El-Behaedi, Danielle Arons, Xianyu Zhang, Christine Alewine. Characterization of the protumorigenic role of MSLN in peritoneal metastases in pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3767.

Abstract 104: Identification of the molecular components required for the protumorigenic effect of MSLN in pancreatic cancer

Mesothelin (MSLN) is a GPI-linked protein expressed in &gt;90% of pancreatic adenocarcinomas (PDAC) but not in healthy pancreas nor in the parenchyma of other vital organs. Due to this differential expression, multiple antibody-based therapies are targeting MSLN. The physiologic role of MSLN is yet unknown. The MSLN gene encodes for a precursor protein which is cleaved to produce mature MSLN protein and soluble Megakaryocyte Potentiating Factor (MPF), both of which can be secreted or shed. Previous reports suggested that overexpression of MSLN precursor protein increases tumorigenicity and metastatic potential of PDAC. Here, we have used CRISPR-Cas9 gene editing to delete MSLN from the KLM-1 pancreatic cancer cell line (ΔMSLN) and have examined the growth of these cells compared to mock deleted cells (Mock). The ΔMSLN and Mock cells grew at the same rate both in cell culture and as subcutaneous tumors in nude mice, but ΔMSLN had significantly impaired growth when inoculated into the mouse intraperitoneal (IP) cavity as well as when injected orthotopically into the pancreas. Histological analysis (H&E, Ki67 and Trichrome) showed no significant gross differences between ΔMSLN and Mock IP tumors. RNA deep sequencing analysis comparing ΔMSLN and Mock cell lines showed strong upregulation of MUC-4 in KO cells. Restoration of WT MSLN expression in ΔMSLN cells restored IP growth, however, transduction of a Y318A point mutant could not. Point mutation of Y318 diminished ability of shed MSLN to interact with KLM-1 cells, presumably by impairing association with MUC-16, the only known binding partner of MSLN. To determine the role of mature MSLN and MPF in tumorigenicity, we expressed these proteins separately in ΔMSLN cells and found that neither could restore IP growth, although mature MSLN was appropriately expressed on the cell surface and MPF secreted. This suggests either that both proteins are required for tumorigenicity or that when synthesized individually they are incorrectly processed by the cell. To examine the role of MSLN in tumorigenesis, MSLN KO mouse were bred into the KPC genetically engineered mouse model of PDAC, which spontaneously develops autochthonous tumors. Unlike PDAC patients, KPC typically die from complications of their primary tumors. Loss of MSLN had no effect on the survival of these mice. Effect of MSLN loss on metastasis in this model is currently being evaluated. In summary, we have demonstrated that MSLN enhances the IP growth of PDAC and defined key regions of MSLN important for this activity.

Citation Format: Leela Rani Avula, Michael Rudloff, Danielle Arons, Salma El-Behaedi, Xianyu Zhang, Theresa Guerin, Serguei Kozlov, Christine Alewine. Identification of the molecular components required for the protumorigenic effect of MSLN in pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 104.

Abstract B029: Deletion of mesothelin impairs intraperitoneal growth of pancreatic cancer

The mesothelin (MSLN) protein is expressed in at least 85% of pancreatic adenocarcinomas but not on cells of the healthy pancreas nor in the parenchyma of other vital organs. Due to this differential expression, MSLN has been used as a target for various antibody-based treatments and cancer vaccines. The physiologic role of MSLN is unknown. The MSLN gene encodes for a precursor protein, which is cleaved to produce the mature MSLN protein. Previous reports have suggested that overexpression of MSLN precursor protein may increase tumorigenicity and metastatic potential of pancreatic adenocarcinoma. Here, we have used CRISPR-Cas9 gene editing to delete MSLN from the KLM-1 pancreatic cancer cell line (ΔMSLN) and have examined the growth of these cells compared to mock deleted cells (Mock). The ΔMSLN and Mock cells grew at the same rate both in cell culture and as subcutaneous tumors in nude mice, but had significantly impaired growth when inoculated into the mouse intraperitoneal cavity. Lentivirus transduction was used to restore expression of MSLN in ΔMSLN cells. Transduction of full-length WT MSLN, but not a Y318A mutant, restored intraperitoneal growth. Interestingly, reintroduction of mature MSLN instead of the precursor protein did not restore growth even though it was appropriately expressed on the cell surface. In summary, we have demonstrated that MSLN enhances the growth of pancreatic cancer within the peritoneal cavity and defined key regions of MSLN important for this activity.

Citation Format: Christine Campo Alewine, Michael Rudloff, Danielle Arons, Salma El-Behaedi, Xianyu Zhang, Leela Avula. Deletion of mesothelin impairs intraperitoneal growth of pancreatic cancer [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr B029.

Abstract 4342: Loss of MSLN impairs pancreatic cancer growth in the peritoneal cavity

Mesothelin (MSLN) is a cell surface glycoprotein that is expressed in at least 85% of pancreatic adenocarcinoma but not on cells of the healthy pancreas nor in the parenchyma of other vital organs. Due to this differential expression, MSLN has been used as a target for various antibody based treatments and cancer vaccines. The physiologic role of MSLN is unknown. Previous reports have suggested that overexpression of MSLN may increase tumorigenicity and metastatic potential of pancreatic adenocarcinoma. To further define the role of MSLN in this disease, we deleted MSLN from the human pancreatic cancer cell line, KLM1, using CRISPR/Cas9 gene editing. Successful deletion of MSLN was confirmed via flow cytometry and immunoblotting. Furthermore, KLMΔMSLN cells were rendered invulnerable to the MSLN-targeted immunotoxin, RG7787, which depends on the presence of surface MSLN for cytotoxicity. In cell culture, KLMΔMSLN cells grew at the same rate as control cells. KLMΔMSLN formed subcutaneous tumors in nude mice with the same frequency as control cells and these tumors grew at the same rate. However, when nude mice were inoculated with KLMΔMSLN or control cells intraperitoneally, a marked decrease in tumor burden was observed in cells lacking MSLN. In summary, we have engineered a pancreatic cancer cell line that lacks MSLN and demonstrated that loss of MSLN impairs tumor growth and spread specifically within the peritoneal cavity. Further experiments are in progress to identify the factors contributing to this phenotype.

Citation Format: Michael W. Rudloff, Danielle Arons, Salma El-Behaedi, Rakan Albalawy, Christine Alewine. Loss of MSLN impairs pancreatic cancer growth in the peritoneal cavity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4342. doi:10.1158/1538-7445.AM2017-4342