Increase in Chymase-Positive Mast Cells in Recurrent Pleomorphic Adenoma and Carcinoma Ex Pleomorphic Adenoma of the Parotid Gland

Incomplete excision of pleomorphic adenoma (PA) may result in recurrent pleomorphic adenoma (RPA). Furthermore, long-term neglected PA may become carcinoma ex pleomorphic adenoma (CXPA). In the present study, the relationships between mast cell-derived chymase and these tumors were examined. The tumor tissues of PA consisted of either or both glandular and fibrotic structures. Histological features of RPA were almost similar to those of PA, except that they showed multinodular structures. CXPA is composed of a mixture of PA and carcinoma. The main stromal cells in PA were myofibroblasts, whereas fibroblasts constituted the main cellular portion in the stromal tissue of RPA. Cancer-associated fibroblasts (CAFs) were present abundantly in CXPA. With increased VEGF expression, neovascularization tended to increase in RPA or CXPA. Compared with PA, chymase-positive mast cells, as well as chymase gene expression, were increased in the tumor tissues from patients with RPA or CXPA. SCF, TGFβ1, and PCNA-positive staining was widely observed in these tumor tissues. The above results suggest that mast cell-derived chymase through its direct or cooperative effects with other mediators may participate in the pathophysiology of RPA and CXPA.

Recurrent Pleomorphic Adenoma

This chapter discusses the etiology, clinical presentation, assessment, and treatment of recurrent pleomorphic adenoma. Recurrent tumor following surgery (or any other treatment) usually presents as a recurrent swelling at the primary site, with or without local symptoms. The incidence of recurrence following surgery varies depending on surgical technique, surgeon's experience, duration of follow-up, and clinical integrity. A recurrence rate of less than 1% is generally considered acceptable. The best policy to prevent recurrence of pleopmorphic adenoma is excisional biopsy of the tumor with maximal safe margin and functional neurological preservation. Treatment is determined by the age and physical health of the patient, number of pervious operations, and anatomical extent of the recurrence. Treatment options include observation, local excision, superficial parotidectomy, total conservative parotidectomy, total parotidectomy with resection of the involved nerve and immediate nerve graft (any procedure is followed by radiotherapy), and radiotherapy alone.