Background Given the observed antitumor activity of immune-checkpoint-inhibitors in patients with mismatch-repair deficient (MSI-H) tumors, we hypothesized that deficiency in homologous-recombination-repair (HRR) can also influence susceptibility. Methods Patients with disease progression on standard of care and for whom pembrolizumab had no FDA approved indication received pembrolizumab. Patients with MSI-H tumors were excluded. Objectives included immune-related objective response rate (iORR), progression-free survival (PFS) and 20-weeks-PFS. Pembrolizumab was given every 3 weeks and scans performed every six. We evaluated a triple-stain (FANCD2foci/DAPI/Ki67) functional assay of the Fanconi Anemia (FA) pathway: FATSI, in treated patients’ archived tumors. The two-stage sample size of 20/39 patients evaluated an expected iORR≥20% in the whole population vs. the null hypothesis of an iORR≤5%, based on an assumed iORR≥40% in patients with functional FA deficiency, and < 10% in patients with intact HRR. An expansion cohort of MSI stable endometrial cancer (MS-EC) followed. Exploratory stool microbiome analyses in selected patients were performed. Results Fifty-two patients (45F,7M;50-evaluable) were enrolled. For the 39 in the two-stage cohort, response evaluation showed 2CR,5PR,11SD,21PD (iORR-18%). FATSI tumor analyses showed 29 competent (+) and 10 deficient (−). 2PR,9SD,17PD,1NE occurred among the FATSI+ (iORR-7%) and 2CR,3PR,2SD,3PD among the FATSI(−) patients (iORR-50%). mPFS and 20w-PFS were 43 days and 21% in FATSI+, versus 202 days and 70% in FATSI(−) patients. One PR occurred in the MS-EC expansion cohort. Conclusions Pembrolizumab has meaningful antitumor activity in malignancies with no current FDA approved indications and FA functional deficiency. The results support further evaluation of FATSI as a discriminatory biomarker for population-selected studies.
We report the interim analysis of a phase 1, proof-of-concept study (NCT04689048), to assess the potential clinical utility of an amino acid radiotracer, 18F-fluciclovine PET/CT, as a functional integral biomarker for previously untreated patients with large brain metastases [BM] (≥1 lesion; >2cm) treated with staged stereotactic radiosurgery (SSRS). We reviewed the imaging characteristics from static PET images acquired 10-25 minutes after 18F-fluciclovine injection for the first seven enrolled patients (9 lesions) who completed baseline imaging, and five patients (7 lesions) who completed the treatment course (SSRS). Patients underwent a baseline (pre-treatment) 18F-fluciclovine PET/CT and contrast-enhanced treatment planning brain MRI before 1st SSRS (15 Gy), repeated after 4 weeks (interim; before 2nd SSRS [15 Gy]), and 8 weeks after treatment completion (first follow-up after 2nd SSRS). The median age was 72 years and 57% were female. All lesions exhibited baseline increased 18F-fluciclovine uptake compared to normal contralateral brain. The median baseline lesion diameters and volumes were 2.16 cm (1.76-3.22 cm) and 4.71cc (2.24-10.21 cc). The median baseline SUVmax, SUVpeak, and SUVmean values were 5.78 (2.16-8.79), 3.33 (0.5-2.72), and 1.75 (1.22-5.16), respectively. The median relative changes in diameter and volume were both -2% (-23% to +13% and -60% to +30%, respectively) at the interim scans, and -30% (-44% to +0.2%) and -43% (-94% to +13%), respectively, at first follow-up. Corresponding median relative changes values for SUVmax, SUVpeak, and SUVmean at interim scan were -20% (-73% to +174%), -9% (-75% to +99%), and -14% (-69% to +36%), and at first follow-up -59% (-87% to -21%), -41% (-86% to +11%), and -21% (-79% to +44%), respectively. In conclusion, this proof-of-concept interim study reports 18F-fluciclovine metrics for patients with large BMs, demonstrating interval reduction in PET metrics after SSRS, more than anatomical measurements alone, highlighting the potential of this as an imaging biomarker.
2555 Background: Given the activity of immune checkpoint inhibitors (ICI) in mismatch repair deficient tumors, we evaluated if homologous recombination repair deficiency associates with solid tumor response to ICI. Methods: We conducted a phase 2 trial (NCT03274661) of PEM in metastatic solid tumor patients progressing on standard of care and for whom PEM had no FDA approved indication. We evaluated a triple stain (FANCD2foci/DAPI/Ki67) immunofluorescence functional assay of the Fanconi Anemia pathway (FATSI) in treated patients’ archived tumors as a correlative biomarker. Patients with microsatellite unstable tumors were not eligible. The primary objective was objective response rate (iORR, CR+PR) by Immune Response Criteria, with the hypothesis that patients with FATSI negative tumors will have better clinical outcome. Secondary objectives were progression free survival (PFS), 6 months PFS and survival. PEM was given every 3 weeks and computed tomography scans were performed every 6 weeks. We utilized a two-stage phase II trial design to detect an iORR ≥ 20% in the whole population tested vs. the null hypothesis that the true iORR ≤5%. If ≥ 2 of the first 20 evaluable patients had an objective response the trial proceeded to full accrual of 39 evaluable patients. Outcomes were evaluated according to FATSI staining. Results: 42 patients (40 evaluable) (35F,7M; median age 62[36-83]) enrolled. Median # of prior regimens was 2[1-7]. Primary Dx included ovarian/fallopian (13), endometrial (10), colorectal (3), cervix (2), pancreatic(2), vaginal (2) and 1 each of various others. No unexpected toxicities occurred. Response evaluation showed 2 CR, 5 PR, 11 SD, 22 PD and 2 NE (iORR 18%). FATSI tumor analyses results are available in 34 patients; 25 FATSI positive, 9 negative. 2 PR, 8 SD, 14 PD, 1 NE occurred among the FATSI (+) (iORR 8%) and 2 CR, 2 PR, 2 SD, 3 PD among the FATSI (-) patients (iORR 44%). mPFS and 6m-PFS were 54 days and 12% (3/25) in FATSI (+), versus 248 days and 56% (5/9) in FATSI (-) patients; p = 0.017. Conclusions: PEM has meaningful antitumor activity in non MSI-high malignancies with no current FDA approved indications. Evaluation of FATSI as a biomarker supports a biomarker selected population approach. Clinical trial information: NCT03274661.
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