I would like to thank Quint el al and Kakinuma et al for their letters and making us aware of the article by Quint et al titled “Lung Lesion Doubling Times: Values and Variability Based on Method of Volume Determination.”1 Their article’s focus was on volume determination methods, whereas our article in a recent issue of CHEST (December 2009)2 was on the lack of exponential growth of a subset of lung cancers as shown by growth curves and the implications that this could have on prior studies that advocated using two volume measurements to determine volume doubling time. While their study did include growth curves for 20 lesions, only 13 of those were lung cancers, and although it is difficult to be sure from their growth curves, it appears that most, if not all, of their lung cancers were followed with only three CT scan exams. An early criticism of our manuscript during peer review was that it would be difficult to prove or exclude exponential growth based on only three data points, and it was recommended that we include only cases with at least four CT scan exams. Therefore, although Quint and colleagues did generate growth curves, it is our position that based on peer review feedback they did not plot growth curves that were analogous to the curves we plotted. We did perhaps err in not referencing the paper and explaining our reasoning. We do agree with their conclusion that “given the very slow growth of some lung cancers, short term follow-up CT may not always be capable of detecting volume changes indicative of malignancy. Therefore, stability on short term follow-up exams should be interpreted with caution.” However, based on our study we would expand on that to caution that even using a volume doubling equation based on two exams could potentially be misleading since the assumption of exponential growth has been called into question.