Intratumoral Injection of mRNA-2752 and Pembrolizumab for High-Risk Ductal Carcinoma In Situ

Importance Intratumoral immunotherapy that leverages the biological characteristics of high-risk ductal carcinoma in situ (DCIS) may be able to reduce the extent of surgical treatment and provide an alternative approach to improve patient outcomes. Objective To determine if combination intratumoral immunotherapy can activate immune cells to shrink or eliminate high-risk DCIS. Design, Setting, and Participants This phase 1 open-label nonrandomized clinical trial at a single academic center tested the safety and efficacy of intratumoral immunotherapy in patients with high-risk DCIS, defined as at least 2 of the following present: younger than 45 years, tumor size greater than 5 cm, high-grade, palpable mass, hormone receptor (HR)–negative, or ERBB2-positive. Patients were enrolled between June 8, 2021, and December 13, 2022. Intervention Pembrolizumab (anti–programmed cell death protein 1), dose ranging from 2 mg to 8 mg, and mRNA-2752 (a combination of interleukin [IL]-23, IL-36γ, and OX40L mRNAs), dose ranging from 1 mg to 4 mg, delivered intratumorally, with 2 to 4 doses given 2 to 3 weeks apart. Main Outcomes and Measures The primary objective was to evaluate the safety and tolerability of intratumoral injections of pembrolizumab and mRNA-2752. The secondary objectives were to assess radiologic and pathological responses and immunological and histological differences in the posttreatment tumor microenvironment. Results Ten female patients with high-risk DCIS (median [range] age, 46 [35-80] years) were enrolled. The median (range) tumor size was 5.3 (1.0-10.0) cm. Five tumors were HR-negative ERBB2-positive; 2 HR-negative ERBB2-negative; 2 HR-positive ERBB2-negative; and 1 HR-positive ERBB2-positive. Of all treated patients, 8 of 10 responded to treatment, and all 8 patients had ERBB2-positive or HR-negative DCIS. Three patients had complete responses. Three patients with negative posttreatment core biopsy results declined surgery and remained disease-free after 1 to 2 years. Multiplex immunofluorescence staining demonstrated that high baseline levels of tumor-infiltrating lymphocytes and programmed cell death ligand 1–positive cells (immune or tumor) were associated with a better treatment response. All patients experienced up to 1 week of fever, malaise, flulike symptoms, axillary adenopathy, erythema, injection site swelling, and swelling in the breast. One patient had intermittent urticaria for 3 months. The dose was serially reduced from 8 mg to 2 mg for pembrolizumab and 4 mg to 1 mg for mRNA-2752 to improve tolerability. The final recommended combination dose is pembrolizumab, 4 mg, with mRNA-2752, 1 mg. Conclusions and Relevance In this phase 1 nonrandomized clinical trial, the results suggest that intratumoral injections of pembrolizumab and mRNA-2752 are safe and may induce rapid regression of high-risk DCIS with high immune infiltrates. These findings warrant additional investigation, and studies are ongoing. Trial Registration ClinicalTrials.gov Identifier: NCT02872025