192 Chapter 6 The DOI cutoff value > 4 mm used in the Erasmus MC as an indication for END, was investigated by assessing the association between DOI > 4 mm and proven as well as occult LNM using ROC curve analysis (1). Statistical analyses The Chi-squared test, non-parametric Fisher’s exact test and independent-Samples T-test were used to compare the patient and tumor characteristics of the LUMC and Erasmus MC cohorts. To calculate the proportion of MET positive cancers within the whole pN+ group (occult and overt LNM), the Chi-squared test was used. The same was done for DOI > 4 mm. To calculate the proportion of MET positive cancers within the occult LNM group (cN0/pN+), the Chi-squared test was used. The same was done for DOI > 4 mm. Binary logistic regression was performed to investigate whether MET positivity and/ or DOI have a – joint – effect on LNM. Calculations were performed with SPSS Statistics (version 25; IBM; Armonk, NY, USA). Unless otherwise mentioned, statistical significance was set at p-value <0.05. Results Comparison of the LUMC and Erasmus MC patient and tumor characteristics The 102 patients included in this study were treated for primary pT1-2 OTSCC with surgery and – if indicated – postoperative radiotherapy in the LUMC or Erasmus MC across different periods. Twenty-five (24.5%) patients were treated in the LUMC and 77 (75.5%) in the Erasmus MC. Comparison of the patient and tumor characteristics as well as MET positivity shows that there are no differences between the two centers (Supplementary table 1). OS and DFS were also similar (results not shown). Association of MET positivity and DOI with LNM in D1C2 positive cancers Hundred and two (102) patients were treated with tumor resection and a neck dissection. Thirty (29.4%) were pN+, of which 20 (66.7%) were cN0 and therefore occult metastases (Table 1).
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