Early CT and FDG-metabolic tumour volume changes show a significant correlation with survival in stage I-III small cell lung cancer: a hypothesis generating study.

Background: Many patients with stage I-III small cell lung cancer (SCLC) experience disease progression short after the completion of concurrent chemoradiotherapy (CRT). The purpose of the current study was to evaluate whether CT or FDG metabolic response early after the start of chemotherapy, but before the beginning of chest RT, is predictive for survival in SCLC.

Methods: Fifteen stage I-III SCLC patients treated with concurrent CRT with an FDG-PET and CT scan available before the start of chemotherapy and after or during the first cycle of chemotherapy, but before the start of radiotherapy, were selected. The metabolic volume (MV) was defined both within the primary tumour and in the involved nodal stations using the 40% (MV40) and 50% (MV50) threshold of the maximum SUV. Metabolic and CT response was assessed by the relative change in MV and CT volume, respectively, between both time points. The association between response and overall survival (OS) was analysed by univariate cox regression analysis. The minimum follow-up was 18 months.

Results: Reductions in MV40 and MV50 were -36±38% (126.4 to 68.7cm(3)) and -44±38% (90.2 to 27.8cm(3)), respectively. The median CT volume reduction was -40±64% (190.6 to 113.8cm(3)). MV40 and MV50 changes showed a significant association with survival (HR=1.02, 95% CI: 1.00-1.04 (p=0.042); HR=1.02, 95% CI: 1.00-1.04 (p=0.048), respectively), indicating a 2% increase in survival probability for 1% reduction in metabolic volume. The CT volume change was also significantly correlated with survival (HR=1.01, 95% CI: 1.00-1.03, p=0.007).

Conclusions: This hypothesis generating study shows that both the early CT and the MV changes show a significant correlation with survival in SCLC. A prospective study is planned in a larger patient cohort to allow multivariate analysis, with the final aim to select patients early during treatment that could benefit from dose intensification or alternative treatment.