Should all nasopharyngeal carcinoma with masticator space involvement be staged as T4?

The prognostic significance of the involvement of anatomical masticator space (MS) in nasopharyngeal carcinoma (NPC) was retrospectively reviewed.

1104 Patients with non-metastatic NPC treated with radical radiotherapy between 1998 and 2010 were re-staged according to the 7th edition of the American Joint Committee on Cancer (AJCC) staging system; tumors with medial pterygoid muscle (MP) and/or lateral pterygoid muscle (LP) involvement but did not fulfill the criteria for T3 or T4 were staged as TX. The tumor volume data, dosimetric data and survival endpoints of different T stage diseases were analyzed and compared to study the significance of MS involvement.

The overall MS involvement rate was 61.0%. The median volumes of the primary gross tumor volume were 9.6ml, 15.2ml, 19.9ml, 32.6ml and 77.3ml for T1, T2, TX, T3 and T4, respectively (p<0.001). T1, T2 and TX tumors received higher minimum dose to the gross tumor volume and planning target volume than T3 and T4. Multivariate analysis showed that age, gender, T-/N-classification and the use of chemotherapy were significant prognostic factors for various survival end-points. Patients with TX disease had similar survival rates as with T1-T2; and had a significantly better 5-year overall survival rate (86.6% vs. 76.6%; p=0.013) and a trend of higher 5-year distant failure-free survival rate (91.5% vs. 81.3%; p=0.09) than patients with T3 disease.

NPC with the involvement of MP and/or LP alone should be classified as T2 disease.