Over‐expression of stromal periostin correlates with poor prognosis of cutaneous squamous cell carcinomas

Periostin, an extracellular matrix macromolecule implicated in tumorigenesis, serves as a prognostic marker for many cancer types. However, there are no data on periostin expression in cutaneous squamous cell carcinoma (cSCC). This study examined periostin expression in patients with cSCC and explored its clincopathological relationship and prognosis. Using immunohistochemistry and ImageJ analysis, we compared periostin expression in 95 cSCCs across a spectrum of cSCC aggressiveness: cSCC in situ (SCCIS) (n = 25), low-risk cSCC (LR-cSCC) (n = 26), high-risk cSCC (HR-cSCC) (n = 38), and cSCC in recessive dystrophic epidermolysis bullosa patients (RDEB cSCC) (n = 6). Immunohistochemistry demonstrated periostin expression within the intra-tumoral stroma but not within tumor cells. Periostin levels significantly (P < 0.001) increased from SCCIS, LR-cSCC, HR-cSCC to RDEB SCC. The stroma of most of the cSCCs we evaluated contained cancer-associated fibroblasts with a myofibroblastic (α -SMA-positive) phenotype. Co-localization of periostin with α-SMA, evidence of fibroblast periostin expression, and absence of keratinocyte or tumor cell periostin expression suggest that, in cSCC, periostin is a product of the peritumoral microenvironment and not the tumor cells themselves. Our data indicate that fibroblast periostin expression is highly correlated with the aggressiveness of cSCC, and may thereby provide a molecular marker that will be useful for subtyping and diagnosing cSCCs according to their biological nature.