Phase IB study of Avelumab and whole brain radiotherapy in patients with leptomeningeal disease from solid tumors: Results and molecular analyses.

[BACKGROUND] Leptomeningeal disease (LMD) from solid tumors has a dismal prognosis, even following treatment with anti-PD-1 therapy. We performed a phase IB study evaluating the safety of Avelumab with whole brain radiotherapy (WBRT) in LMD (NCT03719768).

[METHODS] Fifteen patients were enrolled with LMD from breast, lung, nasopharyngeal, ovarian, and pancreatic tumors. Patients were treated with Avelumab with WBRT, with the first infusion of Avelumab starting 14 days pre-WBRT and continuing during and post-WBRT for up to 5 cycles. Primary endpoints were safety and 3-month OS (OS3). Secondary endpoints included assessment of immune cells in the cerebrospinal fluid (CSF) using single-cell RNA-sequencing (scRNA-Seq) pre- and post-last treatment of Avelumab.

[RESULTS] DLTs occurred in 2 patients, ie, adrenal insufficiency, hypothyroidism, and pneumonitis. Treatment-related toxicities occurred in 5 patients with grade 1/2 and 5 patients with grade 3/4. Immune-related adverse events occurred in 5 patients with grade 1/2 and 3 patients with grade 3/4. The OS3 was 67% (10 of the 15; 95% CI: 38%-84%). Median-OS was 3.85 months (95% CI: 0.9-34.4 months) and median-PFS was 3.85 months (95% CI: 0.9-12.1 months). scRNA-Seq analysis of CSF pre- and post-last-treatment showed Avelumab + WBRT stimulated an adaptive immune response associated with a decrease in regulatory T cells (Tregs), among other changes in the expression of immune checkpoints on CD8 + T cells and macrophages.

[CONCLUSIONS] The combination of Avelumab and WBRT is safe and demonstrates activity in patients with LMD. The identification of high levels of Tregs and macrophages in the CSF of LMD patients offers future avenues for therapeutic development.