Role of Radiotherapy for Malignant and Recurrent Parotid Neoplasms

In recent years radiotherapy has been added to surgical excision in a variety of situations. Some have proposed its use as adjuvant therapy for all malignancies, for all pleomorphic adenomas, for recurrent pleomorphic adenomas only, for malignancy metastatic to the parotid gland, and for those occasions in which there is known spillage of pleomorphic adenoma cells during the course of a superficial parotidectomy.

Radiotherapy is recommended widely as an adjuvant modality after surgical excision of malignant neoplasm. It is used for patients with adenoid cystic carcinoma because of its effectiveness in controlling perineural invasion.13 Studies have shown the results of combined therapy to be superior to surgery alone.16,17 The observed success with adenoid cystic carcinoma has prompted the recommendation for surgery plus radiotherapy for all malignant salivary gland tumors except for T1 or T2 N0 disease with low-grade histology and clear margins.18 A large Scandinavian study19 reported that the change from surgery alone to surgery plus radiotherapy resulted in increased facial nerve preservation and a significantly higher rate of local control. Studies have shown that the addition of radiotherapy has reduced the local recurrence rate by 50% in some clinical reports. Truelson3 recommends the addition of radiotherapy to surgical excision for patients with advanced tumors, high-grade malignancy (squamous cell carcinoma, undifferentiated carcinoma, malignant mixed tumors, and high grade mucoepider-moid carcinoma) as well as for patients with recurrent tumors or suspected residual tumor cells.

The value of radiotherapy as a routine adjuvant for pleomorphic adenoma is unclear. A study from Norway20 reported that in a series of 238 patients with follow-up averaging 18 years, there was an overall recurrence rate of pleomorphic adenoma of 2.5%. The recurrence rate increased to 8% when there was a known rupture of the tumor capsule. Buchman et al.21 concluded that the addition of radiotherapy is extremely important when the surgical pathologist reports inadequate resection margins on the tumor specimen. These investigators observed recurrence in 36% of patients who were not irradiated and no recurrence in the group of patients receiving postoperative radiotherapy. He also recommends postoperative radiotherapy for those patients who have undergone enucleation as the initial surgical procedure and after all patients undergoing surgical excision of recurrent pleomorphic adenoma.

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