15039 Background: Early evaluation of response to primary chemotherapy (PSC) in epithelial ovarian cancer (EOC) pts could allow to administer a proper number of cycles in order to obtain optimal results. Arianna Project 02 is aimed to investigate early tumor response to PSC correlating a set of routine and experimental hystological, biological and gene-expression profile data with clinical data before, during and after PSC. Methods: Stage III-IV EOC received 6 cycles of carboplatin AUC 5 and paclitaxel 175 mg/m2 and are evaluated at baseline and before each cycle by 18FDG-PET, CA 125, circulating tumor cells and experimental circulating bio-markers. Ultrasounds, CT scan and pelvic MRI are done at baseline and every other cycle. This preliminary report is focused on the correlation between changes of PET and CA 125 serum levels and pathological response. Results: Up to now 6 out of 11 pts completed PSC and surgery. Baseline tumoral 18FDG uptake expressed as Standardized Uptake Value (SUV) and CA125 were abnormal in all pts (SUVmax range: 12.1–20; CA 125 range: 416–2026 U/ml, upper normal limit 35 U/ml). One complete and 4 partial pathological remissions > 90% and one no change were observed. Mean (with range) SUVmax and CA125 decrease (Δ SUV and Δ CA125) measured after the 1st, 2nd, 3rd and last cycle of PSC in the 5 responders are similar (table). In the non-responder SUV decreased by 63% after the 1st cycle of PSC, but increased to baseline value after the 2nd cycle and remained unchanged until surgery, while CA 125 progressively decreased from 416 U/ml to 47 U/ml. Conclusions: These preliminary findings indicate that the behaviour of PET and CA 125 in responders are similar. More data are necessary to define the role of PET in the early evaluation of response to PSC in EOC pts. The study is still ongoing and the relationship between evaluation performed by PET and CA125 and by CT scan, ultrasound and pelvic MRI will be presented at ASCO meeting. [Table: see text] No significant financial relationships to disclose.