In order to investigate the source of IL-38 and its localisation with each immune cell in prostate cancer tumour tissues, immunofluorescence double-staining of IL-38 with tumorigenic epithelial cells (P504S+) with each immune cell (CD138+ plasmacytes, CD3+ T cell, CD68+ macrophages, and CD20+ B cell) was performed. The gene discussed is SDC1; the disease is prostate carcinoma.