European Radiology: Nasopharyngeal carcinoma classification is not far enough to know only TNM!

Nasopharyngeal carcinoma (NPC) is a common type of head and neck malignancy, with 129079 newly diagnosed cases worldwide in 2018, with a high
incidence in Southeast Asia.
To reduce recurrence and metastasis, simultaneous radiotherapy (CCRT) and induction chemotherapy (IC)
were introduced clinically.
At the same time, a staging system was introduced to guide clinical risk stratification of patients to achieve optimal treatment
.
However, in the eighth edition of the American Joint Commission on Cancer (AJCC) nasopharyngeal carcinoma staging system, the imbalance in the distribution of T2 and T3 classes led to overlapping
patient outcomes.
Therefore, the current class T needs to be optimized
.

The basilar skull bone is one of the most frequently violated structures during posterior extension of nasopharyngeal carcinoma, with an incidence of 50-70%, which is considered a hallmark
of the T3 category.
Previous studies have shown that the subclassification of skull base invasion (SBI) is an important prognostic predictor of NPCs, but SBI is not ideally
positioned in the current T-staging system.
Therefore, adjusting the T class of SBI subclassification may solve the problem of
overlapping prognosis of T2/T3 class.

Recently, a study published in the journal European Radiology recruited a large number of NPC patients to explore the value of SBI subclassification in prognostic stratification and IC treatment, and further verified its optimal position in the current T staging system, which provides a reference for accurate risk stratification and prognosis assessment of NPC patients in clinical practice
.

This study retrospectively evaluated 1752 patients with nasopharyngeal carcinoma in two hospitals.

Eight skull base bone structures were evaluated
.
Random-matched pair analysis compared survival differences and the presence or absence of ICs between mild SBI (T3 patients with only pterygopalatine process and/or sphenoid base invasion) and severe SBI (T3 patients with other SBIs).

The prognosis of the revised class T and the Harrel consistency index (C-index) were calculated, and the IC results
of the revised tumor stage were compared.

Mild SBIs showed better 5-year overall survival (OS) (81.
5% vs.
92.
3%, p = 0.
001) and progression-free survival (PFS) (71.
5% vs.
83.
0%, p = 0.
002)
compared to severe SBI.
Additional IC treatment did not significantly improve OS and PFS
for mild SBIs.
The proposed class T separates the survival rates of OS, PFS, and no local recurrence for classes T2 and T3 and is statistically significant
.
Compared to the AJCC T staging system, the proposed class T has an improved C index for OS prediction (0.
725 vs.
0.
713, P = 0.
046)
when confounders are combined.
The survival advantage of ICs is more pronounced
in the late stages.

Figure of normal skull base bone structure, illustrating representative MRI images
of mild SBI and severe SBI in patients with nasopharyngeal carcinoma.
Axial (a), coronal (b), and sagittal (c) images show normal skull basal bone position
.
Signs of mild SBI are the pterygoidal process (pink, bone between the medial and lateral extension lines of the pterygoid jaw plate) and the sphenoid base (green) – the sphenoid bone between the medial edges of the bilateral pterygoid jaw processes (coronal position), before the anterior edge extension line of the dentate position (sagittal position).

The structures associated with severe SBI are the apical (yellow), dentate process (blue), large wing of the sphenoid bone (purple), occipital condyle, cervical spine, and paranasal sinuses
.
The bilateral ptar process (white arrow) and the base of the sphenoid bone (green arrow) are violated by the tumor (*), manifest as low signal on axial (d) and crown (e) T1WI, and enhance (f)
on fat inhibition enhancement T1WI.
Example of nasopharyngeal carcinoma patient with severe SBI (g-i): the left flap apex (yellow arrow), dentate process (blue arrow) and sphenoid wing (white arrow) are violated by the tumor (*), Low signal on axial (g) and coronal (h)T1WI, and enhanced fat suppression on T1WI (i).

This study suggests that subclassification and reclassification of SBIs facilitates accurate prognostic stratification and individualized treatment regimens
.
The mild SBI group is recommended for T2 because of the better prognosis for OS and PFS, and similar
survival outcomes for patients treated with or without IC.
After redistribution, the proposed T classification has high predictive value for OS and is an important evaluation index
for whether IC needs to be used.

Original source:

Shuqi Li,Chao Luo,Wenjie Huang,et al.
Value of skull base invasion subclassification in nasopharyngeal carcinoma: implication for prognostic stratification and use of induction chemotherapy.
DOI:10.
1007/s00330-022-08864-7