Breast Cancer Responses During Mistletoe Extract and Intratumoral Influenza Vaccine Treatment

What happened, in summary

A 57-year-old woman was first diagnosed with right invasive ductal breast cancer in March 2010. She underwent lumpectomy and sentinel lymph-node biopsy. The tumor was estrogen- and progesterone-receptor positive and HER2-negative. She declined re-excision for a positive margin, radiation, and endocrine therapy. A local recurrence was diagnosed in 2014, and she again declined standard treatment. By December 2019, imaging showed extensive progression in the right breast, a lesion in the left breast, lymph-node involvement, a single bone metastasis, multiple lung metastases, and pleural metastases, establishing Stage IV disease. Biopsies from both breasts remained strongly hormone receptor-positive and HER2-negative. She declined recommended palliative mastectomy and endocrine therapy with a CDK4/6 inhibitor. In April 2020, she began monthly intravenous and high-dose subcutaneous mistletoe extract treatment. Across 17 cycles through September 2021, some treatments also included intratumoral mistletoe extract and intratumoral influenza vaccine. Follow-up imaging in September 2021 showed a mixed response: lung and bone metastases and several other sites had resolved on imaging, while residual right-breast disease remained and a new left adrenal lesion was suspicious for progression. She declined further radiologic follow-up but remained in good condition without clinical evidence of further progression.