11528 Background: Chondrosarcoma is one of the most common bone malignancies in adults, and the third most common in pediatric patients (pts). The most prevalent subtype, conventional chondrosarcoma, is a slow growing tumor that is historically known to be refractory to chemotherapy. Anecdotal reports indicated a role for anti-PD-(L)1 in the treatment of this disease. This is the first prospective report on the efficacy of the PD-L1-targeting agent, atezolizumab, in this rare disease. Methods: Patients (pts) ages 2 and older with unresectable grade 2 or 3 conventional chondrosarcoma were eligible. No prior anti-PD-(L)1 treatment was allowed, otherwise pts were eligible irrespective of prior therapies as long as protocol-specified washout period requirements were met. Pts received atezolizumab 1200 mg (15 mg/kg with 1200 mg cap in pediatric pts) once every 21 days. Imaging was carried out at end of cycle 3, and then every two cycles. Research biopsies were collected from adult pts prior to C1D1, prior to C3D1, and at progression. Immuno-pharmacodynamic (IO-PD) studies were performed on paired tumor samples and circulating immune cells to help elucidate signaling pathways mediating the immune response, with focus on subsets of effector cells in the tumor microenvironment. Results: A total of 9 pts (7 males, 2 females) were enrolled in 6 centers across the US and Canada. Six pts were Caucasian/White, 1 Asian, 1 Hispanic, and 1 unknown. Median age was 49 years (42-72). No objective responses were seen. Three pts (33%) experienced disease stability (SD) per RECIST 1.1, for a median duration of 21 weeks as of data cutoff (January 2022). A patient with SD remains on active treatment (tx) for 35 weeks. Three patients had no tx-related adverse events (AEs). Six pts (67%) experienced at least one tx-related AE. Two patients experienced > G2 AEs, but only one was considered tx-related (lymphopenia). Immune-related AEs were all G1/2 and included hepatitis (2), hypothyroidism (1), hyperthyroidism (1), and maculopapular rash (1). IO-PD studies are ongoing and will be reported at the conference if available. Conclusions: Atezolizumab was well-tolerated but demonstrated limited activity in this cohort of pts with few treatment options. Ongoing IO-PD studies will provide insight into atezolizumab’s effect upon immune cell content and activation in the tumor microenvironment that will help design future immunotherapy trials in this disease and other sarcoma types. The study was funded by NCI Contract HHSN261201500003I. Clinical trial information: NCT04458922.
11607 Background: Validated biomarkers of response to immune checkpoint inhibitors are needed. Methods: INSPIRE (NCT02644369) is a biomarker-driven study to comprehensively evaluate changes in genomic and immune landscapes in tumors and blood of patients (pts) treated with pembro at 200 mg IV Q3W. It consists of 5 histological cohorts of 20 evaluable pts each: head and neck squamous cell cancer (SCCHN), triple negative breast cancer (TNBC), high grade serous ovarian cancer (HGSOC), melanoma (MM) and mixed solid tumors (MST). All pts undergo pre- and on-treatment (week 6-9) fresh tumor biopsies (bx), and at progression for responders. The first core bx is for immunohistochemistry and subsequent cores are pooled to create single cell suspension for 5 prioritized biomarker assay groups: (1) whole exome/RNA-/TCR-sequencing; (2) T/B/NK, APCs, and/or Treg phenotyping; (3) patient-derived xenografts; (4) RNA-seq on viably sorted immune populations; (5) TIL expansion and characterization. Serial blood samples for immunophenotyping, chemokines/cytokines and ctDNA are collected. Results: 53 pts were enrolled from March 21, 2016-January 16, 2017 (5 SCCHN, 8 TNBC, 17 HGSOC, 7 MM, 16 MST). 84 tumor bx (53 pre-, 30 on-treatment, 1 progression) and 244 blood-based biomarker samples have been collected. The most common sites of tumor bx were: lymph nodes (27%), liver (22%) and skin (14%) (see table). For the 5 cohorts, the % of tumor bx with sufficient cellularity for biomarker assay groups 1 and 2 are: SCCHN (33%), TNBC (9%), HGSOC (52%), MM (55%), MST (55%). Conclusions: This report provides robust technical feasibility data to plan immune and molecular characterization of tumor and blood-based biomarkers in pts receiving ICI. Clinical trial information: NCT02644369. [Table: see text]
11547 Background: Surgery and (neo)adjuvant radiotherapy are the mainstay curative treatments for localized STS. Despite treatment, approximately 50% of STS patients (pts) experience metastatic relapse and routine use of adjuvant systemic therapy (AST) remains controversial. The presence of ctDNA following curative treatment of STS is a potential biomarker for MRD and may identify patients who benefit from AST. Given the genomic heterogeneity of STS, a histology-agnostic approach to ctDNA detection in this population is desirable. Methods: Pts with localized, high risk (size ≥ 5cm, grade ≥ 2) disease were enrolled prior to (neo) adjuvant radiotherapy and surgery. Blood for ctDNA was collected at diagnosis; post-radiotherapy, post-surgery and every 3 months for up to 2 years. Whole exome sequencing (WES) of archival tumor- and matched buffy coat-DNA were carried out to identify somatic variants. Personalized and tumor-informed, multiplex PCR next generation sequencing-based ctDNA assay (Signatera™ assay) was performed on plasma obtained at the serial timepoints. A sample level positive call required ≥ 2 variants above a confidence calling threshold. Absolute ctDNA levels were expressed as mean tumor molecules per milliliter (MTM/ml) of plasma, based on variant allele frequencies and quantity of cell free DNA. Standard radiologic surveillance (every 3 months) was performed following surgery. The primary endpoint was a ctDNA detection rate of 70% at diagnosis. Secondary endpoints included MRD detection and correlation of ctDNA levels with disease relapse. Results: Seventy-six plasma samples from 10 pts [8 males and 2 females; median age 64 years (range 46–84)] were obtained prospectively. STS subtypes were undifferentiated pleomorphic sarcoma (n = 4), myxofibrosarcoma (n = 2), dedifferentiated liposarcoma (n = 2), myxoid liposarcoma (n = 1), and pleomorphic liposarcoma (n = 1). All tumors successfully underwent WES with adequate data quality for Signatera™ assay design. The personalized ctDNA assay was performed on a median of 7 plasma samples per patient (range: 5 – 10). ctDNA was detected in 7 pts (70%) at diagnosis, with median ctDNA level of 1.6 MTM/ml (range: 0.2 – 137.8), achieving the study primary endpoint. Immediate post-surgery samples were negative in all pts. However, ctDNA was detected in 2 out of 2 pts who developed metastatic disease during follow-up. Conclusions: Personalized tumor-informed ctDNA assays in localized high-risk STS at diagnosis are feasible. In this series, all patients had undetectable levels of ctDNA post-surgery and patients who experienced disease relapse demonstrated a detectable rise in ctDNA levels. Further interrogation of this approach for detection of post-treatment MRD as a possible biomarker of benefit from AST is ongoing.
Abstract Background: The molecular mechanisms underlying primary versus acquired resistance to anti-PD-1/L1 antibodies have not been comprehensively evaluated across different tumor types. Methods: The Immune Resistance Interrogation Study (IRIS; NCT04243720) is a prospective, investigator-initiated study at the Princess Margaret Cancer Centre, aimed to perform extensive multi-omic characterization of solid tumors with primary resistance (disease progression on first imaging; or stable disease <6 months) versus acquired resistance (partial or complete response; or stable disease ≥6 months) to antiPD-1/L1 agents. A one-time fresh tumor biopsy is collected from patients (pts) who have progressed on anti-PD1/L1 antibody-based treatment as their most recent line of therapy; liquid biopsy or archived FFPE tissue is allowed as alternates when fresh biopsy is insufficient. NGS was performed using Foundation One (324 genes) or Foundation Liquid (309 genes) panels. Frequencies of disrupted genes and variants were compared in pts with primary versus acquired resistance using Fisher’s exact test. The planned samples size of IRIS is 100 pts. Results: Among the first 35 pts enrolled, 22 (63%) had primary resistance and 13 (37%) had acquired resistance. The most common diagnosis was melanoma (17 pts; 49%); followed by head and neck squamous cell carcinoma (13 pts; 37%); endometrial cancer (2 pts; 6%); pleural mesothelioma, gastroesophageal junction and colorectal cancer (1 pt each; 3%). Foundation One was performed in 23 pts (66%), 22 of them (63%) had biopsies with sufficient quality for NGS, and 1 (3%) had the analysis performed using archival FFPE tissue. The remaining 12 pts (34%) had Foundation Liquid testing done using liquid biopsy. Thirty-three pts (94%) had at least one oncogenic alteration. Genes most frequently altered included: TP53 in 16 patients (46%), TERT promoter in 12 pts (34%), CDKN2A in 9 pts (26%), PIK3CA in 6 pts (17%), and PTEN in 5 pts (14%). At the variant level, the most frequent alterations were: TERT promoter -146C>T mutation in 6 patients (17%), followed by TERT promoter -124C>T mutation in 5 patients (14%), FGF19/FGF4/FGF3 and CCND1 amplifications in 4 pts each (11%), and MDM2 amplification, CDK4 amplification and CDKN2A loss, detected in 3 pts each (9%). Pts with acquired resistance had a higher frequency of TP53 mutations (9/13 = 69%) compared to primary resistance pts (7/22 = 32%), p=0.04; however this was not significant when corrected for multiple testing. Interestingly, amplifications in CDK4, CCND1, FGF 19/FGF 3/FGF 4, MDM2 and mutations in NF1 were only identified in pts with primary resistant tumors. Conclusions: No significant differences in disrupted genes and variants were observed in the current analysis. However, this can be due to the small number of pts analyzed thus far. Accrual to this study is ongoing. A comparison of alterations in oncogenic pathways is planned to further define the genomic landscape of pts with primary versus acquired resistance to anti-PD1/PDL1 blockade. Citation Format: Sofia Genta, Farnoosh Abbas Aghababazadeh, Ming S Tsao, Aaron R Hansen, Marcus O Butler, Albiruni R Razak, Philippe L Bedard, Ben X Wang, Pugh J Trevor, Sevan Hakgor, Jeffrey Woo, Benjamin Haibe-Kains, Lillian L Siu, Anna Spreafico. Immune resistance interrogation study (IRIS): Initial report of next generation sequencing (NGS) results in patients with primary versus acquired resistance to anti-PD1/L1 antibodies [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr LBA021.
11557 Background: Patients have limited treatment options following initial chemotherapy failure. INT230-6, a novel formulation of cisplatin (CIS) and vinblastine (VIN) with an amphiphilic cell penetration enhancer, is designed for intratumoral (IT) administration. Study IT-01 (BMS # CA184-592, NCT 03058289) evaluates INT230-6 alone or in combination with ipilimumab (IPI), an antibody to CTLA-4. INT230-6 dosing is set by a % of the volume of the tumor to be injected. The product has been shown to disperse throughout an injected tumor and diffuse into cancer cells. Cell death leads to recruitment of dendritic and T cells, the effect of which may be augmented by CTLA-4 inhibition as evidenced by increased efficacy of the combination in preclinical models. Historically, checkpoint inhibitors have limited activity in sarcoma. Considering the large volume of drug injected and retained in the tumor, coupled with immune infiltration on biopsies, RECIST response methodology may not capture the benefits of INT230-6 treatment. Methods: IT-01 is an open-label phase 1/2 study that is enrolling adult subjects with locally advanced, unresectable or metastatic sarcoma. INT230-6 was administered IT Q2W for 5 doses alone or with IPI 3mg/kg IV Q3W for 4 doses. The study objectives are to assess the safety and efficacy of IT INT230-6 alone and in combination with IPI. Results: 16 heterogenous sarcoma subjects (13 monotherapy, 3 IPI combination) having a median of 3 prior therapies (0, 8) were enrolled to date. The INT230-6 dose was up to 145 mL (72.5 mg of CIS, 14.5 mg VIN) in a single session (an amount of each agent in excess of standard IV doses). The most common ( > 20%) related TEAEs in sarcoma subjects (n = 16) were localized pain (63%), fatigue (38%), decreased appetite (31%), nausea (31%), and vomiting (25%) most of which were low grade; with only grade 3 TEAE above 5% being anemia (13%). There were no related grade 4 or 5 TEAEs. In 11 evaluable monotherapy subjects, the disease control rate (DCR = CR+PD+SD) was 82%. Basket studies of sarcomas, including chordoma, with Royal Marsden Hospital index (RMHI) scores of 2 or higher report median overall survival (mOS) of 4 months. In this study 75% of monotherapy subjects had a RMHI score of 2 and preliminary estimates of mOS was 21.3 (4.67, NA) months. Pilot immunohistochemistry analysis of 5 paired (pre- and 28 days post-dose) biopsy samples showed substantial tumor necrosis, reduction of viable cancer, a decreased cancer proliferation as measured by Ki67, and increased TILs. Conclusions: Preliminary data shows that INT230-6 administered intratumorally alone or in combination with ipilimumab is well-tolerated in this small, heterogenous sarcoma population. The preclinical cancer cell death and immune infiltration mechanism of action appears to translate to sarcoma subjects. There are early signs of efficacy, DCR and potentially OS, that need to be confirmed in randomized studies. Clinical trial information: 03058289.
The standard treatment of choice for malignant pleural mesothelioma is chemotherapy with pemetrexed and platinum, but the clinical outcome is poor. This study investigates the response to pemetrexed in a panel of eight mesothelioma cell lines and the clinical outcome for patients treated with pemetrexed in relation to folate receptor alpha (FRalpha).Cell lines were treated with pemetrexed to determine the concentration that reduced growth to 50% (GI(50)). FRalpha expression was determined by western blotting and that of FRalpha, reduced folate carrier (RFC) and proton-coupled folate transporter (PCFT) by real-time quantitative RT-PCR. Immunohistochemistry for FRalpha was carried out on 62 paraffin-embedded samples of mesothelioma from patients who were subsequently treated with pemetrexed.A wide range of GI(50) values was obtained for the cell lines, H2452 cells being the most sensitive (GI(50) 22 nM) and RS5 cells having a GI(50) value greater than 10 microM. No FRalpha protein was detected in any cell line, and there was no relationship between sensitivity and expression of folate transporters. FRalpha was detected in 39% of tumour samples, generally in a small percentage of cells. There was no correlation between the presence of FRalpha and the outcome of pemetrexed treatment, and no significant difference between histological subtypes.Response to treatment with pemetrexed does not depend on the presence of FRalpha.
2542 Background: Limited data exist in the clonal dynamics of serial ctDNA as a predictive biomarker in advanced solid tumor pts receiving immune checkpoint blockade. Methods: Pts with mixed solid tumors received single agent P (anti-PD-1) 200 mg IV Q3wks in the investigator-initiated phase II INSPIRE trial (NCT02644369). ctDNA was assayed at baseline (B) and start of cycle 3 (C3) using a pt-specific amplicon-based NGS assay (Signatera™). Samples were considered ctDNA positive if ≥2 of 16 pt-specific targets met the qualifying confidence score threshold. Results: Results of 70 pts are presented. Demographics: male 46%; median age=60 yrs (range 21–82); head and neck (20%), triple negative breast (14%) and ovarian (14%) cancers comprised the major malignancies. Median no. of P cycles=4 (range 2–35); follow up was 14m (range 2–29); RECIST responses: CR 2.9% (n=2), PR 17% (n=12), CBR (CR+PR+SD≥6 cycles) 31% (n=22), RECIST/clinical PD (n=43/10; 65%/15%). Median PFS=3.3m and median OS=17.8m. 68/70 pts had ctDNA detected at baseline (median=16/16 variants) demonstrating 97% sensitivity. Table shows correlation of ΔctDNA (ctDNA B compared to ctDNA C3 ) with clinical efficacy parameters, whereas ctDNA B values did not reach statistical significance. Conclusions: A strong correlation exists between ΔctDNA with OS, PFS, CBR and ORR with P, suggesting it is a potential predictive biomarker in pts with mixed solid tumors. Clinical trial information: NCT02644369. [Table: see text]
