IgG4 Positive Plasma Cells in Sclerosing Variant of Mucoepidermoid Carcinoma: A New and Evolving Concept
W Tian, E Yakirevich, A Matoso, D Gnepp. Alpert Medical School of Brown University, Providence, RI
Background: IgG4-related sclerosing disease is a recently described syndrome with unique histological features characterized by intense lymphoplasmacytic infiltrates with increased IgG4+ plasma cells, & dense stromal sclerosis. The disease spectrum frequently includes benign inflammatory diseases, such as sclerosing pancreatitis, cholangitis & chronic sclerosing sialadenitis (CSS). Mucoepidermoid carcinoma (MEC) is the most common primary malignancy in the salivary gland. The rare sclerosing variant of MEC is characterized by dense stromal sclerosis & lymphoplasmacytic infiltrates. Our goal was to further characterize lymphoplasmacytic infiltrates with respect to IgG4 expression.
Design: Six sclerosing MECs from our pathology service over the past 20 years were selected. In addition, 11 regular MEC with lymphoplasmacytic infiltrates, 4 CSS, & 12 cases of non-sclerosing chronic sialadenitis (CS) were evaluated. Formalin fixed paraffin embedded sections were stained for IgG4 & IgG by IHC. Images were captured under 400X magnification that correspond to a field area of 0.0675 mm2. The number of IgG & IgG4 positive plasma cells was quantified in the same field from five different areas, & the IgG4+ to IgG+ ratio was calculated.
Results: The 6 sclerosing MECs were characterized by prominent sclerosis & dense lymphoid predominantly peritumoral infiltrates rich in plasma cells. None of sclerosing MEC patients had IgG4-related sclerosing disease. The absolute number of IgG4+ plasma cells was significantly increased in sclerosing MEC as compared to regular type (75 vs 20 per image field, P<0.05). Furthermore, the ratio of IgG4+/IgG+ plasma cells was markedly elevated in sclerosing MEC as compared to the regular type (46.5 vs 17, P<0.005). In CSS, absolute numbers of IgG+ plasma cells & IgG4+/IgG+ ratio were significantly increased as compared to CS (P<0.005).
|Sclerosing MEC n=6 Mean (range)||MEC n=11||CSS n=4||CS n=12|
|IgG4||75 (18-190)||20 (3-42)||52 (7-108)||2 (0-11)|
|IgG||172 (54-279)||108 (23-212)||88 (37-152)||63 (3-288)|
|IgG4/IgG||46.5 (22-75)||17 (5-33)||54 (30-79)||4.5 (0-23)|