Neutron radiotherapy for recurrent pleomorphic adenomas of major salivary glands

Pleomorphic adenoma is the most common neoplasm arising in the salivary glands. Surgical management is the primary therapeutic modality. With the use of modern surgical techniques, recurrence is infrequent, and facial nerve sparing is the norm. However, for patients with recurrent disease, the risk of further relapses is increased with surgical resection alone, particularly for those patients in whom multiple recurrences have already occurred. The role of adjuvant radiotherapy in this setting remains uncertain. Although neutron radiotherapy is superior to conventional radiotherapy for malignant salivary gland tumors, its role in the treatment of pleomorphic adenomas is less well defined. We report our experience using this modality for high-risk, recurrent pleomorphic adenomas.

Sixteen patients were treated with neutron radiotherapy for recurrent pleomorphic adenomas of major salivary glands from 1986 through 1993. The median age at diagnosis was 33 years (range, 11-77 years); median age at the time of neutron radiotherapy was 52 years (range, 22-77 years); median number of prior surgical procedures was 3 (range, 1-6); median duration from initial diagnosis to radiotherapy was 14.5 years (range, 3 months-30 years); median follow-up was 83 months (range, 9-144 months). The median period at risk for survivors was 96 months (defined as the interval from completion of neutron radiotherapy to last follow-up). Ten patients had evidence of gross residual disease at the time of treatment as determined by imaging studies, with nine patients having multinodular disease.

The 10-year actuarial survival was 79%. One patient died from lung metastases 9 months after treatment; one patient died from a liver tumor of uncertain origin, but the histology could not rule out a metastasis from the previous pleomorphic adenoma; and one patient died from recurrent disease at the base of skull. The 15-year actuarial locoregional control rate was 85%. One of the two patients with locoregional recurrence had a malignant transformation into an adenocarcinoma. No statistical difference in 15-year actuarial survival (75% vs 83%, p =.82) was found comparing patients with gross residual disease vs microscopic residual disease. The actuarial 15-year locoregional control was 76% for patients with gross residual disease vs 100% for those with microscopic disease. The 15-year actuarial risk of RTOG/ESTRO nonaudiologic grade III/IV complications was 21%. No facial nerve injuries were observed as a direct consequence of neutron radiotherapy.

Neutron radiotherapy offers both excellent local control rates and survival rates in patients with multiply recurrent pleomorphic adenomas that are not candidates for surgical resection, even in the presence of gross residual disease. The treatment-related morbidity is acceptable. Malignant transformations and metastases, although uncommon, may be observed in this tumor.