Response to chemotherapy in patients with lung metastases: how many nodules should be measured?

Objective: With the introduction of cross-sectional imaging methods the number of lesions per patient that can be evaluated is frequently large and most oncologists and study protocols use only one lesion or a few ‘representative’ lesions to evaluate chemotherapy response. Intra-patient response variability can therefore affect evaluation reproducibility. This study evaluates intra-individual variation in response to chemotherapy in patients with multiple lung metastases. Methods: We prospectively studied chest CT images of patients with solid tumors and pulmonary metastases under systemic chemotherapy being evaluated for tumor response. The response of 566 pulmonary nodules in 41 evaluations was determined by both WHO and RECIST criteria in order to determine intra-individual tumor response variation. Results: There was almost perfect agreement between the WHO and the RECIST criteria for the evaluation of tumor response. High intra-individual variability of tumor response was observed in a significant proportion of the evaluations. A new nodule was the main criterion for determination of disease progression. A mean of 35% of the total number of nodules of a patient have a response evaluation different from that calculated with all the nodules together. Conclusions: Intra-individual variation in tumor response of pulmonary metastases is elevated in some patients. Selecting any or some nodules for response evaluation could significantly influence therapeutic response perception.