Oral Abundance of <b><i>Actinomyces</i></b> spp. in Breast Cancer Patients

Objectives: Pathophysiology of medication-related osteonecrosis of the jaw (MRONJ) is still unclear, and disease development is associated with adverse reaction of bisphosphonates and denosumab, and Actinomyces spp. as well. In this study, we evaluated the abundance of Actinomyces spp. in breast cancer patients undergoing chemotherapy compared to healthy controls. Methods: Oropharyngeal samples were collected from treatment-naive early-stage breast cancer patients, who were scheduled for standard of care therapy (eight samples throughout chemotherapy, one prior to radiotherapy and one after a year of start), as well as from healthy controls at matched timepoints. We quantified Actinomyces spp. in the samples with a highly sensitive and specific quantitative polymerase chain reaction. Results: Twenty-one patients and 16 healthy subjects were enrolled. Forty-eight percent of patients suffered from estrogen receptor-positive/progesterone receptor-positive or -negative/human epidermal growth factor receptor 2 (HER2)-negative disease, 38% were HER2-positive, and 14% were triple-negative. Comparison of Actinomyces spp. loads in cancer patients and healthy controls did not reveal significant difference. Fluctuations on bacterial quantity were observed in both groups over time. Tumor receptor status or different chemotherapy schemes of patients were not correlated with a particular pattern on abundance of Actinomyces spp. Conclusions: We suggest that Actinomyces spp. are not the initiative factors in MRONJ development. These bacteria are not altered in abundance during chemotherapy, but they behave opportunistic when there is a bone disruption in the oropharynx in the first place caused by antiresorptive drugs or dental trauma and proliferate in their new niche. Thus, Actinomyces spp. plays a latter role in MRONJ development, rather than a primary causative one.