Koos Boeve

46 Chapter 2 We previously stated that a tumour infiltration depth of 4 mm could serve as an optimal cut-off between elective and therapeutic neck dissections, on the basis of results obtained with the same cohort [6]. Therefore, it is not surprising that the 8 th edition pT2 patients (tumour infiltration depth of 5-10 mm) showed shorter survival in this study. Furthermore, another study suggested using a 4 mm tumour infiltration depth as a cut-off for pT3 tumours instead of the 8 th edition AJCC pT cut-offs [9]. Twelve patients in this cohort had a watchful waiting of the neck and an infiltration depth of >4 mm because they were treated before the introduction of the 4 mm cut-off in our centre. Exclusion of these 12 patients resulted in a 100% 5-year survival for the remaining watchful waiting patients and similar survival stratifications for the 7 th and 8 th pT and pN categories (Supplementary data 1 and 2). The benefit of this cohort was the availability of long-term follow-upbecause no adjustments were made for OSCC in the 7 th pTNM classification edition when it was released in 2009, as compared with the 6 th edition [11]. Additions to the pTNM classification are useful if they can be measured robustly and have a clinical impact. The national guidelines in The Netherlands support postoperative radiotherapy of T3-T4 tumours, even those with clear margins [12]. If the patients in this cohort had been staged with the 8 th edition and treated accordingly, another 3% of the patients would have received postoperative radiotherapy. Although the patients who were restaged according to the 8 th edition pT classification criteria showed lower DSS, prospective studies are needed to confirm that radiotherapy is beneficial for these patients. Besides the adjuvant therapy, SLNB is currently used as staging technique for cT1-2N0 patients in our centre [13]. This study shows that the 30 (15%) patients who were restaged as T3 would not have had an indication for a SLNB according to the 8 th edition criteria. Den Toom et al. stated that 8 th edition pT3 patients with tumours ≤40 mm in diameter probably benefit from staging of the neck with the SLNB procedure [10]. However, further data are needed to verify whether the SLNB is still a reliable neck staging technique for patients restaged from 7 th edition pT1-T2 to 8 th edition pT3. In our centre, pN3 patients are treated postoperatively with concomitant chemoradiotherapy according to the current guidelines [12]. Despite the better prognostic value of the 8 th edition pN classification, pN staging with the 8 th edition would not alter postoperative treatment strategies in our centre. The growth of OSCCs can occur in an exophytic, an ulcerative or a superficial manner [2,6]. These differences in surface growth have resulted in various methods of assessment of tumour infiltration depth and thickness in the past[2]. To prevent underestimation (ulcerative growth) or overestimation (exophytic growth) of the prognosis, for the 8 th pT classification tumour infiltration needs to be measured vertically from the reconstructed mucosa by use of the adjacent mucosal basement membrane of the normal epithelium [2].