Dendritic Cell Therapy Shows Promise in Early HER2-Positive Breast Cancer

At the American Society of Clinical Oncology (ASCO) meeting, phase II findings suggested that intratumoral dendritic cell therapy combined with HER2-targeted treatment may enhance immune activity and improve pathologic complete response rates in patients with early-stage HER2-positive breast cancer.

In this MedPage Today “Future Focus” video, Hyo Han, MD, of Moffitt Cancer Center in Tampa, Florida, discusses the study findings, including circulating tumor (ct)DNA clearance, as well as the ongoing chemotherapy-free trial evaluating this approach.

Following is a transcript of her remarks:

In ASCO 2026, we have reported phase II neoadjuvant clinical trial data, including patients with HER2-positive early-stage breast cancer. We have previously reported and published a phase I study using dendritic cell therapy in combination with HER2-targeted therapy for the same patient population, reporting that dendritic cell therapy combined with HER2-targeted antibodies is safe and effective in altering the tumor microenvironment, inducing increased tumor regression in early-stage HER2-positive breast cancer.

So in this phase II clinical study, 47 patients, 24 hormone receptor-positive/HER2-positive, and 23 hormone receptor-negative/HER2-positive, early-stage breast cancers were enrolled at Moffitt Cancer Center between May of 2022 and October of 2025.

Primary endpoint of this study was pathologic complete response following neoadjuvant treatment for clinical trial, and it was 50% for hormone receptor-positive subgroup and 83% in hormone receptor-negative subgroup. So dendritic cell vaccines were made from patient blood collected using procedure called apheresis and cells were trained with HER2 peptide that led to mature dendritic cells that was injected into the patient’s breast tumor directly every week, six times in combination with the trastuzumab [Herceptin] and pertuzumab [Perjeta].

And after 6 weeks of initial immunotherapy, patients received chemotherapy using weekly paclitaxel in combination with the trastuzumab and pertuzumab for 12 weeks. So treatment was a total of 18 weeks. And after following initial neoadjuvant therapy, all patients underwent main surgery, including either lumpectomy or mastectomy.

And in terms of toxicity related to dendritic cell therapy was consistent with what was previously reported with manageable toxicity, including flu-like symptoms and some injection site discomfort.

In this study, we also have evaluated circulating tumor DNA using a personalized tumor-informed assay, Signatera, and baseline levels were available for 27 patients. And 16 of those patients had a positive ctDNA at baseline. And of those patients, 76.5% of patients cleared ctDNA with neoadjuvant therapy prior to surgery. And also 70% of patients cleared their ctDNA after only 6 weeks of dendritic cells in combination of Herceptin and Perjeta treatment without chemotherapy portion as well. We also have reported preliminary data showing that increased T-cell infiltration and tumor regression on patient biopsy in this poster.

So in conclusion, intratumoral dendritic cell therapy in combination with trastuzumab-pertuzumab prior to neoadjuvant paclitaxel, Herceptin, and Perjeta therapy in early-stage HER2-positive breast cancer was well tolerated with manageable toxicity and it led to increased, enhanced immune cell infiltrations and ctDNA clearance with improved pathologic complete response in this patient population.

So we’re very excited to report this at ASCO this year and continue to follow up in this study. At Moffitt Cancer Center, we are currently conducting a clinical study using chemotherapy-free neoadjuvant therapy in the same patient population. So current ongoing clinical trial is using dendritic cell intratumoral therapy in combination with Herceptin and Perjeta HER2-targeted therapy only for 12 weeks without paclitaxel chemotherapy. So we are very excited to have this clinical trial ongoing based on the study reported.