Chemotherapy-associated oral microbiome changes in breast cancer patients

Abstract

Cytotoxic chemotherapy with or without a combination of humanized monoclonal antibodies is regarded as the gold standard of personalized medicine for the treatment of breast cancer patients. Significant medication-related side effects are common accompanying phenomena for these patients, such as oral discomfort, mucositis, or even osteonecrosis of the jaw. In this study, we analyze the saliva samples of 20 breast cancer patients at three time points throughout their chemotherapy: at the baseline prior to treatment initiation (T1), after four-to-six cycles of chemotherapy (T2), and 1 year after the start of the treatment (T3) to investigate and characterize the long-term effects of chemotherapy on the oral microbiome. We aimed to characterize changes in the oral bacterial microbiome based on 16S rRNA gene amplicon analysis during chemotherapeutic treatment, as a potential target to treat common oral side effects occurring during therapy. The chemotherapeutic drugs used in our study for patient treatment were trastuzumab, docetaxel, pertuzumab, epirubicin, and cyclophosphamide. We find a significant increase in the relative abundance of potentially pathogenic taxa like Escherichia/Shigella and non-significant trends in the relative abundance of, for example, Actinomyces ssp. In conclusion, the role of microbiota in the oral side effects of chemotherapeutic treatment needs to be considered and should be analyzed in more detail using larger patient cohorts. Oral side effects in breast cancer patients undergoing chemotherapy are a common burden and should be treated for a better tolerability of the therapy.

Keywords: 16S rRNA gene amplicon analysis; Actinomyces; chemotherapy; microbial pattern; oral microbiome; oral side effects.

Figure 1

Alpha diversity calculations over all groups of (A) richness (pvalue > 0.05), (B) Shannon (pvalue > 0.05), and (C) Simpson (pvalue > 0.05) diversity index at the phylum level. T1: before/at start of chemotherapy, T2: 12 weeks after the onset of chemotherapy, T3: 52 weeks after the onset of chemotherapy.

Figure 2

Bar charts of relative microbial abundance at the (A) phylum and (B) genus levels per sample group (the 20 most abundant taxa are shown). T1: before/at start of chemotherapy, T2: 12 weeks after the onset of chemotherapy, T3: 52 weeks after the onset of chemotherapy.

Figure 3

Beta diversity calculations at phylum level characterizing the intersample difference: (A) Chao, (B) Bray–Curtis as well as (C) Jaccard indices. Confidence ellipses indicate a 95% confidence level. (D) Abundance heatmap plotting to visualize hierarchical clustering on the six most dominant taxa at the order level. Colors from blue to red indicate feature abundance in the log scale. T1: before/at start of chemotherapy, T2: 12 weeks after the onset of chemotherapy, T3: 52 weeks after the onset of chemotherapy.

Figure 4

(A) The normalized counts of the phylum Firmicutes and (B) Actinobacteriota. Normalized counts are plotted; *indicates pvalue < 0.05. T1: before/at start of chemotherapy, T2: 12 weeks after the onset of chemotherapy, T3: 52 weeks after the onset of chemotherapy.

Figure 5

Genera with significant differences in normalized counts between sample groups: (A) Escherichia/Shigella, (B) Megasphaera, (C) Prevotella, and (D) Streptococcus, one of the most abundant genera. *indicates pvalue < 0.05. **indicates pvalue < 0.01. T1: before/at start of chemotherapy, T2: 12 weeks after the onset of chemotherapy, T3: 52 weeks after the onset of chemotherapy.