Characterization of skin microbiome profile before and during radiation therapy and its correlation to the occurrence and severity of radiation dermatitis

Purpose/objective(s): The purpose of study is to characterize the skin microbiome profile of breast cancer patients before and during radiation therapy, and evaluate the relationship between the microbiome profile and the severity of acute radiation dermatitis (aRD). Materials/methods: In this observational, single-center, single-arm study, breast cancer patients received RT at Rambam Health Care Campus from November 2020 to July 2021. Skin assessments and skin microbiome samples were collected from all patients before, weekly during RT, after completion of the treatment. The outcome measures were: aRD grade, skin microbiome composition at baseline and during RT. Results: 640 skin samples were collected from 86 patients, bacterial DNA was extracted, and 16S rDNA was amplified and sequenced.At mid-treatment, the bacterial family Clostridiaceae was unique to patients later diagnosed with moderate/severe acute dermatitis, and present in 30% of the samples (p-value = 0.002038). An unknown species of Anaerococcus, designated Anaerococcus US436, was unique to patients in the moderate/severe aRD group at mid-treatment (21.67% in this group, p-value = 0.002038).To increase sample size and reduce noise, we collected all treated samples from all time points and compared the microbiome composition between the groups of dermatitis severity. The Clostridiaceae family and Clostridium genus remained significantly enriched in the moderate/severe group (p-value = 0.002095 and 0.004269, respectively), as well as the Anaerococcus genus and its unknown species (p-value = 0.001825 and 0.007104, respectively).The treated samples for each patient were summed up, and each bacterium was examined for at least one appearance per patient during the treatment. Granulicatella elegans was enriched in the moderate/severe group (p-value = 0.000512), and Bacillus thuringiensis was enriched in the mild group (p-value = 0.000595). Conclusion: A bacterial composition associated with moderate/severe aRD was identified: Clostridium, Anaerococcus US436, and Granulicatella elegans.