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Ann Thorac Surg 2005;79:384-385
© 2005 The Society of Thoracic Surgeons
Northern General Hospital, Herries Rd, Sheffield S5 7AU, UK
Nottingham City Hospital, Hucknall Rd, Nottingham NG5 1PB, UK
Northern General Hospital, Herries Rd Sheffield S5 7AU, UK
alexiou486{at}aol.com
To the Editor:
We thank Dr Birdas for his interesting comments and the Editor for giving us the opportunity to reply.
It should be stressed that the "early" survival difference between the pneumonectomy and the smaller lung resection groups was 5.6% (operative mortality of 8% versus 2.4%). Figures 1 to 3 reveal the following: In figure 1, the overall survival difference (T1N0 and T2N0 tumors included) between the pneumonectomy and the smaller lung resection groups at 1, 2, and 3 postoperative years was 19%, 19%, and 16%, respectively. In figure 2, after lung resection for T1N0 disease, the survival difference between the two groups at 1, 2, and 3 postoperative years was 18%, 31%, and 33%, respectively. In figure 3, the differences in the survival between the two groups for T2N0 tumors at the previously stated time intervals were 18%, 14%, and 7%, respectively. Thus, it would appear that our statement that "the survival difference continues to increase over the first 2 or 3 postoperative years" is in keeping with the data presented [1].
Dr Birdas correctly points out that "all three survival curves shown have overlapping 95% confidence intervals at 3 and 5 years." We would add that this overlap is pronounced in figure 3 as it was acknowledged and stated in the figure legend: "The survival curves overlap 5 years postoperatively (when relatively small numbers of patients remain at risk), but there is a marked difference in the estimated median survival between the groups." In fact this observation demonstrates why is important to include the numbers of patients that remain at risk at various time intervals when displaying Kaplan-Meier survival curves. It should be also emphasized that the survival difference between the pneumonectomy and the smaller resection groups in this study were statistically significant (p < 0.05) when tested with each of the log rank, Breslow, and Tarone-Ware tests (despite the previously mentioned overlap in the 95% confidence intervals after the third postoperative year). Moreover, on multivariate analysis, pneumonectomy emerged as an independent adverse predictor of survival in the overall group (the T1N0 and T2N0 groups).
The statistical methods used in this study were chosen with expert professional assistance and did not include hazard function analysis.
Pneumonectomy has a higher operative mortality than smaller lung resections. Then should operative mortality be included in the survival analysis? Because the purpose of this study was to evaluate the effect of pneumonectomy on early or late survival of patients having stage I nonsmall cell lung cancer (an oncological group with a favorable prognosis after anatomic lobectomy), we feel that it would be inappropriate to exclude the operative mortality from the Kaplan-Meier analysis of survival.
Irrespective of the specific contribution made by the early and late mortality on the overall survival, it is clear that the patients who underwent pneumonectomy for T1N0 or T2N0 NSCLC fared significantly worse than those who had smaller lung resections [1]. These findings should perhaps encourage thoracic surgeons to strive to achieve complete tumor removal using lung resections smaller than pneumonectomy.
References
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