Patterns of lymph node metastasis of parotid cancer

To define the incidence and pattern of spread of lymph node metastasis from parotid cancers and to clarify the risk factors and appropriate extent of neck dissection (ND) for individual patient with parotid cancer.

A total of 72 patients with parotid gland cancer treated by surgery between 1994 and 2013 were analyzed retrospectively by reference to medical records. In line with our protocol, patients with clinically positive lymph nodes and/or cT3/T4 disease were generally selected to undergo ND.

Pathological examinations revealed mucoepidermoid carcinoma in 23 patients, carcinoma ex pleomorphic adenoma in 11, adenoid cystic carcinoma in 9, salivary duct carcinoma in 9, acinic cell carcinoma in 8, squamous cell carcinoma in 5, adenocarcinoma NOS in 4, epithelial myoepithelial carcinoma in 2, and basal cell carcinoma in 1. Thirty-three patients underwent neck dissection: modified radical ND (MRND) in 13, and elective ND (END) in 20. Postoperative RT (PORT) was performed in 33 patients. Among 13 cN+ patients, 10 were pN+ and lymph node metastasis was distributed mainly in levels I, II, III and V. Among 59 cN- patients, clinical T1, T2, T3 and T4 classifications accounted for 10, 24, 10 and 15 patients, respectively. The incidence of occult lymph node metastasis was 22%. Occult lymph node metastasis was mostly seen in the intraparotid, levels I and II of patients with cT4 disease. Among the ND group, 12 necks were pathologically negative for cancer (pN0). Relapse of neck lymph node metastasis occurred only in two patients treated by MRND with pathologically positive lymph nodes (pN+). These patients developed local and distant metastasis within 1 year after neck lymph node recurrence, and subsequently died of the cancer. pN+ was found in 19/30 high grade (63%), 1/10 intermediate grade (10%), and 3/32 low grade (9.4%). Among 33 patients who received PORT, only 1 patient relapsed neck lymph node.

For patients with clinically positive lymph nodes, ipsilateral modified radical neck dissection (levels I-V) is recommended. Elective neck dissection is strongly recommended for patients with T3N0 or T4N0 disease, and the extent of ND should include at least level I/II. PORT for patients with high-risk features may improve the outcome of good neck control.