Lipomatous tumors of the oral mucosa: Histomorphological, histochemical and immunohistochemical features

We conducted a comprehensive study of all lipomatous tumors of the oral mucosa (1996-2008) accessioned at the Department of Oral Pathology, Tel Aviv University, collected demographic data and analyzed multiple histomorphological features. Furthermore, we examined the immunostaining of aP2 (adipocyte lipid binding protein) and the polarization colors of picrosirius red (PSR)-stained collagen fibers in order to test their potential in differentiating between benign and malignant tumors. All cases were immunohistochemically stained with aP2 antibody; only tumors with considerable collagenous stroma were selected for the PSR staining. A total of 77 tumors were included in the study, 91% benign and 9% malignant. Fibrolipoma (37.7%) and lipoma (36.4%) were the most frequent tumors. Atypical lipomatous tumor (ALT) was the only type of malignancy. The most common location for the benign tumors was the buccal mucosa and for ALT, the tongue. Histomorphological features characteristic of malignant tumors were occasionally present also in the benign entities. Expression of aP2 was similar in all tumors, while the polarization colors of the PSR-stained collagen fibers differed significantly between ALT and benign tumors (p<0.05). Benign and malignant tumors occasionally show overlapping histomorphological features that require a meticulous examination. PSR staining with polarization microscopy could aid in differentiating malignant from benign tumors in equivocal cases.