Breaking new ground in ductal carcinoma in situ management: the promise of intratumoral messenger ribonucleic acid-2752 and pembrolizumab

Approximately 20% of breast tumors detected radiographically are ductal carcinoma in situ (DCIS), a preinvasive malignancy (1). Standard treatment includes surgery, adjuvant radiation therapy, and endocrine therapy (2). Although many patients are cured, with overall survival rates approaching 100%, high-risk DCIS lesions [i.e., high-grade, estrogen, progesterone, and human epidermal growth factor receptor 2 (HER2) negative (“triple-negative”) or HER2-positive] are more likely to recur or become invasive. Around 27–35% cases of DCIS are HER2-positive (3), and 25–30% are hormone receptor-negative (HR−) (4). Some high-risk DCIS patients have an approximately 25% risk of developing recurrent DCIS or invasive breast cancer following surgery (5). In addition, patients with HR− DCIS have limited adjuvant systemic therapy options as they do not benefit from adjuvant endocrine therapy (6). As current treatments may cause side effects (pain, suboptimal cosmesis, reconstruction complications, and toxicities related to radiation and endocrine therapy), novel treatment strategies to prevent recurrences and preserve quality of life are needed (7,8).

Immunotherapy activates the host’s immune system to eradicate disease, potentially inducing sustained responses in appropriately selected patients (9). Previous studies in both metastatic and early-stage settings have shown that immunotherapy tends to be more effective when used earlier in the disease course when the tumor immune microenvironment is less suppressive (10). This is reflected in better responses observed with pembrolizumab combined with chemotherapy in early-stage disease compared to the metastatic setting (11-14). Notably, in early-stage disease, pembrolizumab demonstrated benefit regardless of programmed cell death ligand 1 (PD-L1) status—a contrast to the metastatic setting. These findings naturally support the exploration of immune checkpoint inhibitors in even earlier stages, such as DCIS.

This study by Ramalingam et al. describes a novel lipid nanoparticle-encapsulated messenger ribonucleic acid (mRNA)-based vaccine, mRNA-2752, given in combination with pembrolizumab as an intratumoral injection (15). mRNA-2752 encodes three key immune stimulators, including two immune stimulatory cytokines, involving danger signals with interleukin (IL)-23 and tissue damages with IL-36γ, as well as T-cell costimulator OX40L mRNAs. In preclinical data, IL-23/IL-36γ/OX40L triplet mRNA mixture elicited remarkable anti-tumor activity by recruiting multiple types of immune infiltrates, particularly dendritic cells (DCs) and CD8+ T cells. The combination of this triplet mRNA mixture and an immune checkpoint inhibitor given intratumorally resulted in durable tumor regression in several syngeneic mouse models (16). The previous phase 1 trial of intratumoral mRNA-2752 with intravenous durvalumab also demonstrated promising results in patients with advanced solid malignancies (17). This study is a phase I, open-label, non-randomized clinical trial at a single academic institution (NCT02872025) that evaluated mRNA-2752 (dose range: 1–4 mg) with pembrolizumab (dose range: 2–8 mg) in patients with high-risk DCIS, defined by ≥2 of the following characteristics: age <45 years, tumor >5 cm, palpable, grade II–III, abundant T-cell infiltrate, HR−, or HER2-positive. Patients were enrolled between June 2021 and December 2022. Intratumoral injections were administered by breast surgeons via ultrasound guidance or palpation, with 2–4 doses at 2–3 weeks’ intervals. Patients were observed for adverse events (AEs), and contrast-enhanced magnetic resonance imaging (MRI) scans were performed at baseline and 2–3 weeks after the 2nd and 4th injections to evaluate tumor volume changes. Ten female patients were enrolled, with a median age of 46. The majority of patients had large tumors with a median size of 5.3 cm. Remarkably, eight of ten (80%) treated patients had objective responses, including three complete responses (CR 30%), all in patients with HR− DCIS. Two patients who did not respond had HR+ HER2− DCIS with low baseline tumor-infiltrating lymphocytes (TILs). Three patients with CR confirmed by core biopsies elected to defer surgery and remained free of disease progression up to 33 months after treatment. Of 5 patients who had a partial response, two were able to proceed with breast-conserving surgery, avoiding mastectomy. Elevated baseline TILs and PD-L1 positivity were associated with superior treatment responses. Consistent with immune activation, all patients experienced flu-like symptoms that lasted <1 week after the injections. Other AEs were mainly local inflammatory responses, including breast pain, swelling, breast erythema, and axillary lymph node swelling. However, two patients required systemic steroids, with one patient having a grade 3 fever (>104 ℉) for 2 days, with breast and axillary swelling that resolved rapidly with oral steroids. The final recommended combination dose was 4 mg of pembrolizumab with 1 mg of mRNA-2752.

This study compared favorably to previous clinical trials evaluating cancer vaccines in DCIS. These studies used tumor-associated self-antigens such as HER2 and mucin 1 (MUC1) as their targets. Sharma et al. (18) evaluated autologous monocyte-derived DC vaccine pulsed ex vivo with HER2 peptide in a preoperative setting. In this initial trial, a complete pathological response (pCR) was noted in 5/27 patients (18.5%). Similar to this mRNA-2752 trial, a higher pCR rate was observed in patients with HR− DCIS compared to HR+ (40% vs. 5.9%, respectively). In addition, loss of HER2 expression was more likely to be seen in HR− DCIS (50% vs. 43.8%, P=0.01) after the vaccine. These results suggested more effective elimination of HER2− clones in HR− DCIS. A subsequent larger study with 54 patients showed that this HER2 peptide-pulsed DC vaccine was safe and immunogenic in HER2 expressing DCIS (n=42) and invasive breast cancer (n=12) (19). The treatments were given either intratumorally, intranodally, or both. Similar immune and pCRs were observed regardless of the administration route. However, the pCR rate was higher in DCIS vs. invasive breast cancer (28.6% vs. 8.3%). Although the pCR rates were comparable between HR− and HR+ DCIS, all HR+ DCIS patients who achieved pCR had received concurrent endocrine therapy, whereas none of the five patients who did not receive endocrine therapy attained a pCR. This finding suggested that pCR in HR+ DCIS may be attributed to the effects of endocrine therapy.

Another HER2-targeting vaccine that has been studied in DCIS is Nelipepimut-S (NPS). Also known as E75 or NeuVax, NPS is an “off the shelf” nine amino acid human leukocyte antigen (HLA) A2-restricted peptide-based vaccine targeting the HER2 extracellular domain with granulocyte-macrophage colony-stimulating factor (GM-CSF) as an immunoadjuvant. While the results of NPS in the early phase I and II trials were promising (16,20,21), the subsequent phase III PRESENT trial of NPS in patients with HER2 low-expressing node-positive breast cancer in the adjuvant setting was terminated early due to lack of efficacy (22). In a randomized phase II trial evaluating neoadjuvant NPS vs. GM-CSF alone in DCIS (23), NPS was administered every two weeks for two doses prior to surgery. Among the eight patients who received NPS, one patient achieved a pCR, with evidence of persistent NPS-specific T cell activation 1 month after surgery.

To mitigate systemic toxicity associated with standard intravenous administration, several studies have investigated intratumoral delivery. This approach not only achieves higher local therapeutic concentrations, potentially enhancing efficacy, but also functions as an in situ vaccine to amplify T-cell responses (24). In a prior phase I study by this group evaluating intratumoral pembrolizumab as a single agent in nine patients (25), a significant increase in total T-cell and CD8+ T-cell infiltration was observed. However, no objective response was seen by volumetric MRI, and cleaved caspase-3 staining showed no evidence of significant cell death after treatment. Nevertheless, the treatment was well tolerated, with only mild, short-term discomfort at the injection sites. Notably, unlike mRNA-2752, single-agent pembrolizumab did not induce systemic flu-like symptoms or axillary lymph node swelling, suggesting that mRNA-2752, in combination with pembrolizumab, elicits broader systemic immune activation beyond the local injection site.

While the findings of this study are promising, the small sample size represents a key limitation, necessitating validation in a larger patient cohort. Additionally, given the potential for sampling error when assessing response via core biopsies, the study team implemented clinical and imaging surveillance every three months for six months, followed by assessments every six months thereafter to better characterize response trajectories. However, this approach posed challenges for long-term follow-up. Another limitation is the potential high cost and substantial time commitment required in a larger study, which could also present challenges for patient recruitment.

To date, most cancer vaccine research in DCIS has focused on tumor-associated self-antigens, which may lead to limited immune activation due to pre-existing tolerance. In contrast, mRNA-2752 offers an alternative mechanism of immune activation that is independent of antigen expression, making it potentially more broadly applicable across diverse tumor types. In summary, the trial by Ramalingam et al. highlights the potential of intratumoral mRNA-2752 in combination with pembrolizumab for patients with DCIS, particularly those with HR− disease, where systemic treatment options remain limited. The observed AEs were manageable and short-lived. Further investigation in a larger patient cohort is warranted to assess the efficacy of intratumoral mRNA-2752 and pembrolizumab in high-risk DCIS. Leveraging the immune system for treatment may offer a more cost-effective approach with fewer long-term toxicities compared to current standard therapies, while also providing durable protection. These emerging immunotherapeutic strategies have the potential to transform the treatment paradigm, possibly reducing or even eliminating the need for surgery and radiation in DCIS patients.

Acknowledgments

None.

Footnote

Provenance and Peer Review: This article was commissioned by the editorial office, Annals of Translational Medicine. The article has undergone external peer review.

Peer Review File: Available at https://atm.amegroups.com/article/view/10.21037/atm-25-49/prf

Funding: None.

Conflicts of Interest: Both authors have completed the ICMJE uniform disclosure form (available at https://atm.amegroups.com/article/view/10.21037/atm-25-49/coif). C.C.O. has research funding to Mayo Clinic from Pfizer and AstraZeneca. S.C. has research funding to Mayo Clinic from Merck & Co., Pfizer, Salix Pharmaceuticals, Rebiotix Inc., Novartis, and BriaCell Therapeutics. She also receives consulting fees for the advisory board to her institution from AstraZeneca, Daiichi Sankyo, Novartis, Puma Biotechnology, Eisai, Seagen, and Genentech. The authors have no other conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

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