The reduced expression of trimethylation of histone H3 at lysine 27 in primary cutaneous mucinous carcinoma

Primary cutaneous mucinous carcinoma (PCMC) is rare, and its carcinogenesis is unclear. Trimethylation of histone H3 at lysine 27 (H3K27me3) is a key regulator in chromatin remodeling-controlled transcription. Focusing on the epigenetic mechanism, we aimed to investigate the expression of H3K27me3 in PCMC by immunohistochemistry. A retrospective cohort of PCMC patients from a tertiary hospital in Taiwan was enrolled to evaluate the clinicopathologic features, treatment outcome, and protein expression. Immunohistochemistry for H3K27me3 was performed on all PCMCs and a comparison group of colonic mucinous adenocarcinoma and pure mucinous carcinoma of the breast. The percentage of H3K27me3-negative tumor cells was calculated and analyzed. Three patients with PCMC were recruited. All PCMCs were solitary and slow growing, arising from the head-and-neck region. All PCMCs had tumor excision without local recurrence or metastasis. The loss of H3K27me3 expression was significant in PCMCs (mean ± standard deviation [SD]: 21.0% ± 6.6%) compared to other mucinous carcinomas (mean ± SD: 3.8% ± 1.7%) (P = 0.019). In conclusion, we report a reduction in H3K27me3 expression in PCMC. In contrast, H3K27me3 expression is retained or mildly reduced in other mucinous carcinomas. This is the first study to indicate a possible role of epigenetic events in the pathobiology of PCMC.