Correlation between FDG-PET and pathologic response in patients with rectal cancer treated with neoadjuvant chemo-radiotherapy: First results of the Bologna Project

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3623 Background: The aim of the study was to evaluate the predictive value of FDG-PET in patients (pts) treated with neoadjuvant chemo-radiotherapy (CRT) for rectal cancer in the Bologna Project. Methods: Pts entering the study had histologically-proven rectal adenocarcinoma and stage uT3-T4 N-/+ or uT2 N-/+ with inferior location (<5 cm from the anal margin). Chemotherapy (CT) consisted of a weekly schedule of oxaliplatin (OXA) 60 mg/m2 iv for 6 times and 5-fluorouracil (5FU) 225 mg/m2/die protracted infusion iv d 1–38. Radiotherapy (RT) started the same day as CT and was delivered up to a dose of 50.4 Gy in daily fractions of 1.8 Gy (45 Gy in 25 fractions + a boost of 5.4 Gy in 3 fractions). Rectal surgery with total mesorectal excision was performed 6–8 weeks after the end of neoadjuvant treatment. The FDG-PET was performed at initial diagnosis and 6–7 weeks after the end of CRT (before surgery). The pathological examination of surgical specimens included the tumor regression grade (TRG) evaluation according to Mandard. Results: 15 pts were evaluated between June 2003 and October 2004. Pt characteristics were: 11 men and 4 women; median age 66 years (33–77); median Karnofsky PS 100 (90–100); stage: 1 uT2N-M0, 7 uT3N-M0, 4 uT3N+M0, 2 uT3NxM0 and 1 uT4NxM0. The FDG-PET correctly indentified the primary tumor in all 15 pts at initial diagnosis (100% sensitivity). The baseline (pre-CRT) mean Standardized Uptake Value (SUV) of all 15 pts was 18.6 (range 7–51). Pathological responses were as follows: complete response (pT0N0) with absence of tumor cells (TRG 1) in 3 pts; microscopic focus (pTmicN0) with rare residual cancer cells (TRG 2) in 9 pts; fibrosis outgrowing cancer cells (TRG 3) in 2 pts; cancer cells outgrowing fibrosis (TRG 4) in 1 pt. In 12 pT0N0 + pTmicN0 pts (TRG 1–2) the mean SUV after CRT was 2.7 (range 0–4.7) with 83.0% SUV mean decrease compared to the baseline. In 3 pts with TRG 3–4 the mean SUV after CRT was 5.1 (range 4.3–6.4) with 72.2% SUV mean decrease compared to the baseline. Conclusions: These early results suggest that higher % decrease of SUV before surgery in pts with rectal cancer treated with neoadjuvant CRT may be correlated with pathological response. No significant financial relationships to disclose.