Familial Nasopharyngeal Carcinoma 6

Staging of Nasopharyngeal carcinoma 31924.5.4Prevertebral Space InvasionPrevertebral space invasion in NPC suffers from similarproblems as base of skull invasion. Thus againthe entity is heterogeneous and prone to the problemsof “stage creep” resulting from the use of highquality MRI and there may be judgment identifyingthis phenomenon in patients with gross prevertebrallongus muscle invasion (Fig. 24.6). Obviously, theseinvestigations have significant potential to improvethe quality of radiotherapy targeting for affectedpatients. The alternative consequence is that theymake interpretation of the available data problematicfrom a prognostic standpoint, and interseriescomparisons may be challenging. Lee et al. (2008)from Taiwan most recently proposed that prevertebralspace involvement should at least be consideredtogether with the TNM classification to predict prognosisand potentially to influence treatment strategies.In a modest retrospective series where allpatients underwent magnetic imaging of the prevertebralspace (n = 106), these investigators reportedthat 43 patients had baseline prevertebral spaceinvolvement and experienced statistically significantworse overall and metastasis-free survival comparedto the 63 patients without this attribute. In a largerseries, also from Taiwan, Feng et al. reported theexperience of 181 of 521 patients deemed to haveprevertebral muscle involvement. This finding wasassociated with a statistically significant detrimentin loco-regional and distant recurrence, and a borderlinesignificant risk in terms of overall survival(Feng et al. 2006). To what degree the regional anatomyaffects these outcomes needs to be consideredin future studies, and in particular, the significance,if any, of prevertebral muscle vs. space invasion, aswell as the local hematogenous and lymphatic drainagethat may influence the risk of distant metastasis(Feng et al. 2006; Lee et al. 2008). In the same manneras discussed for base of skull and intracranialdisease, the community would benefit from additionalwork in this area to determine if it should beconsidered for inclusion in the future editions of thestage classification.24.6Surrogates of Disease Burden24.6.1Tumor Volume AssessmentFig. 24.6. Axial T2 weighted magnetic resonance imageshows abnormal expansion and signal change in the left longusmusculature (dashed arrow). The contralateral longusmuscle shows a normal slender shape and internal striations(solid arrow)Since the publication of the 5th edition, classificationbased on tumor volume instead of strict anatomicextent alone has been reported as a significant prognosticfactor in the treatment of NPC. In turn, this hasprompted investigators to suggest the incorporationof tumor volume into the TNM staging system.Indeed, an extensive literature has now emerged thataddresses this topic, but will not be discussed exhaustively.Nonetheless, if tumor volume is to be usedas an independent prognostic factor, the methods forvolume measurement need to be standardized(Chong and Ong 2008). Unfortunately, the technicalchallenges to implement this in the clinical settingroutinely need to be resolved if it is to be used to classifypatients using a TNM system. Not only is themeasurement of tumor volume a tedious processrequiring the tumor to be outlined digitally on crosssectionalimaging, but the results are prone to difficultiescreated by both intra and interobserverdiscrepancy. To overcome this problem, several investigatorshave developed semi-automated systems toreduce interoperator as well as intraoperator variability(Chong and Ong 2008). To overcome the technical