Targeted Oncology
Targeted Oncology
Targeted Oncology

Parotid Node Metastases in Locally Advanced Nasopharyngeal and Oropharyngeal Cancer

Terence M. Williams MD, PhD, Jeffrey M. Vainshtein, MD, Matthew E. Spector, MD, et al
Published Online: Aug 23,2016

Implications for Radiotherapy Target Volume Delineation

Abstract



Purpose: To determine the frequency and clinical characteristics of parotid gland metastasis (PGM) from nasopharyngeal cancer (NPC) and oropharyngeal cancer (OPC) and define criteria for elective inclusion of parotidean nodes in the radiotherapy clinical target volume (CTV).

Methods and Materials: All cases of NPC and stage III/IV OPC referred for radiotherapy at our institution between 2003 and 2011 were reviewed. Incidence and risk factors for PGM at presentation and at time of failure were analyzed. A literature review of PGM incidence in head and neck squamous cell carcinoma was performed.

Results: Of 52 NPC and 231 OPC patients, two (3.8%) NPC patients and 4 (1.9%) patients presented with PGM. All PGMs were located ipsilateral to the primary tumors in patients with bulky, ipsilateral level II and multi-level ipsilateral lymph node involvement of aggregate size greater than 6 cm in diameter. Similar rates and characteristics were found in the literature after an extensive search.

Conclusion: The ipsilateral parotidean nodes may be at risk of metastatic involvement when bulky ipsilateral level II metastases and multi-level nodal disease are co-existent, possibly due to retrograde lymphatic drainage. Inclusion of the ipsilateral parotid gland in the CTV should be considered in such cases.
 

Introduction



The most common oral complication and cause for reductions of quality of life (QOL) after head and neck radiation is salivary gland dysfunction and xerostomia.1,2 Parotid gland-sparing intensity-modulated radiation therapy (IMRT) techniques have become standard of care in an attempt to prevent salivary flow dysfunction and xerostomia. IMRT has facilitated parotid-sparing by virtue of enabling steep dose gradients between normal tissue and clinical target volumes (CTV) in close apposition. Indeed, the use of IMRT has increased dramatically in the United States.3 Furthermore, in comparisons between IMRT and conventional radiation for head and neck cancer (HNC), no significant increases in the rate of locoregional relapse have been found with the use of IMRT.4-6 Given the steep dose gradients typical of IMRT, awareness of the risk of involvement to various adjacent sites is critical for appropriate target delineation and avoidance of marginal failures.

While the presence of clinically-evident disease in a parotid gland (PG) precludes its exclusion from the radiation target volume, there has been some controversy as to whether the ipsilateral PG should be spared when it is not clinically involved.4,7 Although the PG should likely be included in the CTV when it is at high risk for sub-clinical disease, no clear clinical factors to-date have been identified to indicate when the PG is at high risk. Others have previously reported recurrences in the region of a spared PG after IMRT.4,5 In a publication by Chao et al, a patient with squamous cell carcinoma (SCC) of the piriform sinus developed a surgical bed recurrence near the spared PG.5 Cannon et al, also reported 3 additional cases of tumor recurrence in the region of the spared PG.4 Two of these recurrences were in peri-parotid lymph nodes (LNs), and the third in the skin near the tail of the spared PG. An additional 3 cases of peri-parotid metastases have been reported by Chen et al,8 with all 3 recurrences occurring in or near the spared contralateral PG. However, the overall frequency of these recurrences has not been well-reported.

In the present study, we sought to identify cases of pathologically-proven PG metastases in patients with previously-untreated nasopharyngeal and oropharyngeal cancer (NPC and OPC, respectively), perform a review of the relevant literature on PG metastases in head and neck squamous cell carcinoma (HNSCC), and determine common clinical characteristics of patients with PGM to generate indications for inclusion of the PG in the CTV.
 

Methods and Materials



This retrospective study was approved by the University of Michigan IRB. Existing databases of all cases of NPC and Stage III/IV OPC presenting for consultation at the Department of Radiation Oncology from 2003-2011 were queried to identify patients with clinical and/or radiological evidence of PG metastases. Cases of SCC metastatic to the parotid when the primary site was unknown were excluded. The presence of metastases within the parotid gland, rather than within level II, was confirmed in all cases by an attending neuroradiologist. Clinical characteristics of patients with confirmed PGM were retrospectively reviewed. A PubMed literature review was performed to determine the incidence of parotid metastasis (PM) from mucosal HNC, and potentially identify clinical factors predisposing patients to metastatic dissemination to the PG.
 

Results



Between 2003 and 2011, 52 patients with NPC and 231 patients with OPC were identified. Of these, 2 of 52 (3.8%) patients with NPC and 4 of 231 (1.7%) with OPC presented with PMs. All PGM were ipsilateral to the primary tumor, and all patients had extensive multilevel ipsilateral nodal involvement with bulky level II adenopathy. Of all nasopharynx and oropharynx cases that presented to us from 2003 to 2011, 33 patients had N3 disease.

Three of the 6 patients with PGM underwent definitive chemoradiation using IMRT at our institution. Of these 3, no LRR has been observed thus far, at a median follow-up of 14 months (range 9-21). In addition, no patient who presented to us with oral cavity, larynx, or hypopharynx primary carcinomas presented with PG involvement. The clinical details of the 6 patients presenting with PGM are discussed below.




Clinical Articles

Parotid Node Metastases in Locally Advanced Nasopharyngeal and Oropharyngeal Cancer
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