Pathologic study of tumour extension for clinically localized unilateral nasopharyngeal carcinoma: Should the contralateral side be included in the clinical target volume?

Introduction: The clinical target volume (CTV) delineation is crucial for tumour control and normal tissue protection. This study investigated the contralateral extension of nasopharyngeal carcinoma (NPC) in patients with a clinically diagnosed unilateral tumour to pursue the possibility of CTV reduction.

Methods: Twenty NPC patients with localized tumours confined to only one side of the nasopharynx as shown by magnetic resonance imaging and fibreoptic endoscopy were selected for biopsy. The tissues of the contralateral pharyngeal recess (CPR) and the contralateral posterosuperior wall (CPSW) of the nasopharynx were obtained in each case and prepared for pathological examination. The factors associated with contralateral tumour infiltration were analysed.

Results: Five of 20 (25.0%) patients were pathologically confirmed to have carcinoma cell infiltration in the CPSW, including 2 (10.0%) that had carcinoma cell infiltration in the CPR. The T classification (P = 0.014) and primary tumour volume (P = 0.033) were positively associated with the infiltration of the CPSW, but none of the primary tumour factors affected the involvement of the CPR. The contralateral retropharyngeal lymph node (LN) metastasis (P = 0.016), but not the contralateral cervical LN, was significantly associated with the infiltration of the CPR. Positive Epstein-Barr virus DNA (EBV-DNA) was another factor that increased the probability of CPR invasion (P = 0.044).

Conclusions: Contralateral pharyngeal recess infiltration is rare in patients with clinically diagnosed unilateral primary NPC. Reduced CTV coverage, including the CPSW but not CRP, is feasible for patients with unilateral cancer of the nasopharynx without contralateral LN metastasis or positive EBV-DNA. Further large-sample studies are needed.