Skin and gut microbial associations with squamous cell carcinoma in solid organ transplant recipients

Solid organ transplant recipients (SOTRs) are burdened with a significantly higher risk of squamous cell carcinoma (SCC) compared to the general population. Accumulating evidence suggests the potential influence of microbial dysbiosis on transplant outcomes. Based on these observations, we sought to identify differences in the cutaneous and gut microbiomes of SOTRs with and without a history of SCC. This case-control study collected and analyzed non-lesional skin and fecal samples of 20 SOTRs > 18 years old with either ≥ 4 diagnoses of SCC since most recent transplant (n = 10) or 0 diagnoses of SCC (n = 10). The skin and gut microbiomes were investigated with Next-Generation Sequencing, and analysis of variance (ANOVA) followed by Tukey pairwise comparison procedure was used to test for differences in taxonomic relative abundances and microbial diversity indices between the two cohorts. Analyses of the skin microbiome showed increased bacterial and reduced fungal diversity in SOTRs with a history of SCC compared to SOTRs without a history of SCC (bacterial median Shannon diversity index (SDI) = 3.636 and 3.154, p < 0.05; fungal SDI = 4.474 and 6.174, p < 0.05, respectively). Analyses of the gut microbiome showed reduced bacterial and fungal diversity in the SCC history cohort compared to the SCC history-negative cohort (bacterial SDI = 2.620 and 3.300, p < 0.05; fungal SDI = 3.490 and 3.812, p < 0.05, respectively). The results of this pilot study thus show a trend toward the bacterial and fungal communities of the gut and skin being distinct in SOTRs with a history of SCC compared to SOTRs without a history of SCC. It furthermore demonstrates the potential for microbial markers to be used in the prognostication of squamous cell carcinoma risk in solid organ transplant recipients.