Zagzag, David

2090 Background: A subset of meningiomas has an aggressive clinical course requiring multimodal therapies. Yet, treatment options beyond surgery and radiation are limited. Somatostatin receptor 2 (SSTR2) is uniformly expressed in meningiomas and can be targeted by the radiopharmaceutical agent [ 177 Lu]Lu-DOTA-TATE ( 177 Lu-Dotatate). [ 68 Ga]Ga-DOTA-TATE ( 68 Ga-Dotatate) PET is emerging as a promising imaging modality to assess treatment response in SSTR2-expressing tumors. However, prospective clinical data supporting the use of 177 Lu-Dotatate and 68 Ga-Dotatate in treatment-refractory meningiomas is limited. Methods: In this multicenter, open-label, phase 2 clinical study (NCT03971461), adult patients with progressive intracranial meningiomas received 177 Lu-Dotatate at 7.4 GBq (200 mCi) every 8 weeks for 4 doses. The primary endpoint was 6-month progression-free survival (PFS-6). Up to 5 meningioma lesions per patient were assessed by gadolinium-enhanced T1 MRI every 12 weeks. 68 Ga-Dotatate PET was obtained before/after 177 Lu-Dotatate treatments. Lesional 68 Ga-Dotatate PET activity was assessed relative to liver/spleen or superior sagittal sinus (SSS). Results: 32 patients (female = 21, male = 11) with progressive meningiomas (WHO grade 1 = 7, grade 2 = 24, grade 3 = 1) were enrolled. Median age was 65.5 (range 41-78) years. All patients had at least one prior tumor surgery and at least one course of radiation. Overall, 177 Lu-Dotatate was well tolerated and the most common grade 3/4 adverse events were transient cytopenia in 15 patients (47%). One patient (3%) discontinued treatment due to grade 4 thrombocytopenia. PFS-6 was reached in 22 patients (69%), which includes 5 of 7 (71%) with grade 1 and 17 of 24 (71%) with grade 2 meningiomas. Best radiographic response by MRI was partial response (PR) in 5 (16%) and stable disease (SD) in 20 (63%) patients. Eight patients (16 lesions) were evaluable by paired MRI and 68 Ga-Dotatate PET pre- and post-treatment. Referenced to SSS, 68 Ga-Dotatate avidity reduced by ≥50% in 2 lesions (PR), 25-49% (minor response, MR) in 3 lesions and remained stable ( < 25% reduction and < 25% increase) in 11 lesions. Using liver/spleen as a reference (6 patients, 14 lesions), 68 Ga-Dotatate uptake was reduced in 9 lesions and stable in 5 lesions. 68 Ga-Dotatate PET assessments were generally concordant with MRI-based treatment response assessments. Conclusions: The primary endpoint (PFS-6) was met in this phase 2 study with 69% of patients achieving PFS-6, thereby surpassing established historical benchmarks. 177 Lu-Dotatate was generally well tolerated and deserves further study in patients with advanced meningiomas. Exploratory 68 Ga-DOTATATE PET studies showed decreased uptake in a subset of lesions and bears promise as an imaging biomarker to assess treatment response. Clinical trial information: NCT03971461 .