2018-19 Section 7-Neoplastic and Inflammatory Diseases of the Head and Neck eBook

J. García et al. / Oral Oncology 70 (2017) 29–33

TNM and 8th ed. TNM pN categories. Differences in survival were compared using the log-rank test. We used measures of hazard discrimination and balance follow- ing the criteria defined by Groome et al. [9] to objectively compare the 7th ed. TNM and 8th ed. TNM. Hazard discrimination measures how evenly the survival curves are spaced for each of the classifi- cation categories, and how large the difference in survival between the best and the worst categories is. The hazard discrimination ranges from zero to 1, where 1 represents an ideal classification with a full coverage of the survival area by evenly spaced curves. Balance quantifies the distribution of the number of patients for the classification scheme in each category. The best classification system is the one with the highest balance. All procedures were reviewed by the Institutional Review Board at Sant Pau Hospital. The study conforms to the principles outlined in the Declaration of Helsinki. We found lymph node metastases in 50.1% of the patients (n = 570). In 50.5% of these cases (n = 288) the pathological report revealed ECS. Table 3 shows the distribution of the patients accord- ing to the pN categories defined by both the 7th and the 8th edi- tions of the TNM Classification. The new staging system produced the upstaging of 20.9% of the patients classified as pN1 to pN2a (n = 33), and of 58.4% of the patients classified as pN2 to pN3b (n = 220). Fig. 1 shows the cause-specific survival curves according to the pN categories obtained with the 7th ed. TNM ( Fig. 1 A) and 8th ed. TNM ( Fig. 1 B). Five-year cause-specific survival for pN2 (35.5%) was very similar to pN3 (21.6%) according to the 7th ed. TNM. The implementation of the changes of the 8th ed. TNM achieves more evenly spread curves. In the new classification, 5-year cause-specific survival for pN2 (53.3%) sits in an more intermediate position between pN1 (70.5%) and pN3 (24.0%). Table 4 shows 5-year cause-specific survival rates for every pN category for both the 7th ed. TNM and the 8th ed. TNM. As expected, the main changes were in the pN2 categories where most reclassifications took place. Fig. 2 B shows the cause-specific survival curves for patients classified as pN2 according the 7th ed. TNM, reclassified by the new criteria in the 8th ed. TNM in two groups depending on the presence or absence of ECS. Five-year cause-specific survival for patients with ECS (n = 217) was 22.4%, and for patients without ECS (n = 157) it was 51.4%. There were statistically significant dif- ferences in survival between the two reclassified groups (P = 0.0001). Inversely, patients classified as pN1 in the 7th ed. TNM did not show survival differences when stratified by the presence of ECS, as proposed in the 8th ed. TNM ( Fig. 2 A). Five-year cause-specific sur- vival for patients with ECS (n = 33) was 63.5%, and for patients without ECS (n = 125) it was 70.5% (P = 0.838). Results

Fig. 1. Cause-specific survival curves stratified by pN category according to 7th ed. TNM (Fig. A) and 8th ed. TNM (Fig. B).

All patients classified as pN3 in the 7th ed. TNM presented ECS, and were reclassified as pN3b in the new classification. In our ser- ies, no patient could be assigned to the pN3a category. According to the results of the objective comparison between both classification systems, the 8th ed. TNM achieved the best val- ues both in heterogeneity in survival between categories (hazard discrimination values: 7th ed. TNM 0.633 versus 8th ed. TN 0.710), and in distribution of the number of cases between cate- gories (balance values: 7th ed. TNM 0.560 versus 8th ed. TN 0.670).

Discussion

According to our results, the inclusion of ECS in the pathological classification of the 8th ed. TNM improved the prognostic capacity of the classification, as compared with the previous version. The objective comparison of both editions showed better results for the 8th ed. TNM in terms of a more even distribution of the

Table 3 Crosstabulation of pathological node classification (pN) in 7th ed. TNM and in 8th ed. TNM.

pN 8 ª

Total

pN0

pN1

pN2a

pN2b

pN2c

pN3b

pN 7 ª

pN0 pN1

567

567 158

125

33

pN2a pN2b pN2c

3

9

12

103

117

220 145

51

94 35

pN3

35

Total

567

125

3

103

51

288

1137

173