![]() ![]() In Figure 2 A, we observed primary splits (LN-MPR 79.7%, events = 34, estimated rate = 1.4). ![]() The recursive partitioning tree graph (the cutoff point) facilitates exploring the structure of a set of data while developing easy-to-visualize decision rules for predicting a categorical (classification tree) or continuous (regression tree) outcome. We, therefore, explored various cutoffs for LN-MPR and found that the optimal cutoff percentage of the viable tumor was 70% as identified by TIBCO Spotfire S-plus software (TIBCO Software, Inc.) ( Fig. 2 A). However, a cutoff for tumor viability in lymph node metastasis has not been established. Results Patient Characteristics and Histologic Tumor Typesġ0% or less viable tumor was not observed in tumors that did not receive neoadjuvant chemotherapy. The statistical analyses were performed using SPSS software (version 15 IBM, Armonk, NY). The recursive partitioning tree graph (the cutoff point) was generated by TIBCO Spotfire S-plus software (TIBCO Software, Inc., Palo Alto, CA). P values less than 0.05 in the multivariable analysis were considered significant. The variables found to be significant in univariable analysis ( p < 0.25) were evaluated by means of multivariable analysis using the Cox proportional hazards model after backward stepwise Wald elimination. A univariable Cox proportional hazards regression model was used to evaluate the association of OS with histologic tumor type and various clinical factors. The log-rank test was used to compare patient survival times among groups. Survival probability as a function of time was computed using the Kaplan-Meier estimator. Disease-free survival was defined as the time from surgery until the time of the tumor recurrence or the date of the last follow-up. ![]() OS was defined as the time from the date of surgery to that of death due to any cause. This approach is similar to that used for the primary tumor and, in the lack of any data, the one proposed in the recent International Association for the Study of Lung Cancer recommendations. The percentage of viable tumor cells in each lymph node specimen was estimated by comparing the estimated cross-sectional areas of the viable tumor with the estimated cross-sectional areas of necrosis, fibrosis, and inflammation on each slide. Figure 1 illustrates a schematic diagram of the histopathologic evaluation of tumor regression in lymph nodes (LN-MPR). Tissue specimens were retrospectively evaluated by two pathologists blinded to the patients’ treatments and outcomes. The number of tumor slides per case ranged from 2 to 12 and the number of lymph node slides ranged from 1 to 15. All lymph nodes were entirely submitted (if ≤0.5 cm in greatest diameter, serially sectioned if >0.5 cm in greatest diameter). The entire primary tumors were only submitted for histologic examination if they were small (≤3 cm). ![]()
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