Expression of Peroxisome Proliferator–Activated Receptor Gamma in Salivary Duct Carcinoma: Immunohistochemical Analysis of 15 Cases

Salivary duct carcinoma is a rare but highly aggressive tumor of the salivary glands that has poor prognosis. There is no effective cure for this tumor. Peroxisome proliferator-activated receptor gamma (PPARγ) is a member of the nuclear receptor family with diverse biological functions that include mediation of adipocyte differentiation, regulation of the monocyte–macrophage anti-inflammatory activity, and inhibition of tumor cell proliferation. Natural (prostaglandin J2, PG-J2) and synthetic (thiazolinediones) PPARγ ligands with anti-proliferative agonist activity have been identified. The expression of PPARγ has been demonstrated in human colorectal, pancreas, breast, and prostate cancers but has never been explored in salivary duct carcinoma. The aim of our study was to investigate the expression patterns of PPARγ in salivary duct carcinoma, a finding that may provide a mechanism for treating patients with this highly aggressive tumor. Archival formalin-fixed tissues from 15 salivary duct carcinoma cases were analyzed for PPARγ expression by an immunohistochemical staining method using a monoclonal antibody against the PPARγ. The tissue sections were subjected to antigen retrieval by a steam heat method. All the cases of salivary duct carcinoma originated from the parotid gland. Immunohistochemistry analyses showed positive expression of PPARγ in 12 (80%) cases, whereas 3 (20%) were negative. Of the positive cases, 9 (75%), 2 (17%) and 1 (8%) showed strong, moderate, and weak staining, respectively. All staining was cytoplasmic. Nuclear staining was not observed. We conclude that PPARγ is frequently (80%) expressed in salivary duct carcinoma, often at high levels, and is topographically located in the cytoplasm. The high-level expression of PPARγ may provide a potential molecular target for the treatment of salivary duct carcinoma using agonist ligands.