Correlation of histologic results with PET findings for tumor regression and survival in locally advanced non-small cell lung cancer after neoadjuvant treatment

CT cannot provide useful information in a timely manner after neoadjuvant treatment. To evaluate the role of F-18 FDG PET after neoadjuvant chemoradiation for early therapy response and its effect on survival as compared to histopathologic tumor response, findings in 32 patients were analyzed prospectively in an ongoing multicenter trial (LUCAS-MD). Inclusion criteria: histologically confirmed NSCLC stage IIIA/IIIB. Neoadjuvant treatment: 2 - 3 cycles with paclitaxel/ carboplatin and a block of chemoradiation followed by surgery. Pretherapeutic staging: PET scan in addition to a spiral CT and/ or MRI. Second PET scan after completion of neoadjuvant therapy prior to surgery. Documentation of lymph node involvement. Assessment of SUV and the metabolic tumor index for primary tumor and metastatic lymph nodes. Image fusion of PET with CT data followed by molecular radiation treatment planning. Evaluation of histologic regression grade and correlation with PET for primary tumor and each lymph node location. All patients (10/32) with complete response in lymph node metastases detected by PET prior to surgery, had no vital tumor cells (i.e. histologic regression grade/ RG III, sensitivity 100%). In primary tumors showing complete response, the RG was IIb or III, in one patient IIa ( false negative in PET). False positive findings in PET are due to inflammation ( 5 patients, histologically confirmed). Univariate analyses: actuarial bolic remission vs. incomplete remission after 24 months: 76 vs. 20% (p = 0,0079); for RG III/ IIb vs. RG IIa/I after 24 months: 63 vs. 36% (p = 0,0123). F-18 FDG PET precedes CT in measuring the tumor response and may predict ( long term) therapeutic outcome in stage III NSCLC. Histologic regression grade correlates well with metabolic remission as detected by PET.