Abstract Book

S805

ESTRO 37

Purpose or Objective Patients with locally advanced rectal caners with suspicious lateral pelvic lymph nodes (LPLN) are associated with have poor local control and higher rate of distant metastasis. There is wide variability in management of these patients regarding the role of LPLN dissection (LPLND). LPLND is not routinely recommended due to excessive surgical morbidity. The aim of this study was to identify the set of patients in whom LPLND is indicated. In this study we analysed the outcomes of all consecutive patients with locally advanced rectal cancer with suspicious LPLN treated at our center Material and Methods Patients diagnosed with locally advanced rectal cancer having suspicious LPLN on MRI treated between June 2013 to 2016 were studied. All received neoadjuvant chemoradiotherapy (NACRT) to pelvis to a dose of 5000 cGy in 25 fractions over 5 weeks with concurrent Tablet Capecitabine (825 mg/m2 bid for 5 weeks). Response evaluation MRI pelvis was done at 6 – 8 weeks post radiotherapy. They were stratified as per the response to NACRT as complete responders (CR) in whom the LPLN were not seen or were < 5 mm. Patients having persistent or suspicious looking LPLN >5mm were labelled as having sub-optimal responders (SR). TME alone was done in patients with CR and LPLND + TME was done in those with SR. Results Sixty patients were included. All had suspicious LPLN of median size 10 mm (range 5 – 34 mm), and bilateral in 23 (38%) patients. Mesorectal fascia was threatened or involved in 32 (52%) of the cases and 41 (67%) had documented N2 disease on MRI. All the patients completed NACRT. Twelve patients were excluded from the study. Post NACRT 5 patients developed additional metastasis, 2 rectal tumor was still unresectable and 5 refused surgery. On response evaluation, MRI 24(50%) had CR at LPLN site so underwent TME alone and in 24 (50%) patients having SR, LPLND was done in 22 patients. The median follow up of all the patients was 27 months (range 10-43 months). 13(27%) patients developed recurrence. Pelvic recurrence developed in 6 (10%); distant metastasis developed in 6 (10%); and both occurred in 1 patients (0.6%). Recurrence correlated to the response of LPLN to chemoradiation. Patients with CR at LPLN only 2 (10%) patients recurred (1 local and one distal), whereas in patients with partial or poor response at LPLN to CRT 10 (38%) recurred (5 local and 5 distal) in spite of undergoing nodal dissection. In univariate analysis, LPLN size of >8mm, response of RT at LPLN and TRG of primary tumor were significantly associated with RFS. Fig 1. Histologic grade and CEA level post CRT were significantly associated with overall survival (P < .05) Table1 Conclusion In patients of locally advanced rectal cancer presenting with LPLN undergoing NACRT if there is a radiological response at the LPLN doing LPLND may be an over treatment. But the patients having persistent LPLN post NACRT have poor outcomes, and more aggressive treatment like complete LPLND is indicated which may result in improved outcomes

EP-1485 Analysis of Clinical Characteristics to Predict pCR for LARC Patients Treated with Neo-CRT B. Wen 1 , C. Wang 1 , H. Peng 1 , J. Dong 1 , Y. Gao 2 1 The First Affiliated Hospital Sun Yat-sen University, Department of Radiation Oncology, Guangzhou, China 2 Sun Yat-sen University Cancer Center, Department of Radiation Oncology, Guangzhou, China Purpose or Objective To explore clinical characteristics which could be used to predict pathologic complete response (pCR) for patients with locally advanced rectal cancer treated with neoadjuvant chemoradiotherapy (neo-CRT) and total mesorectal excision (TME). Material and Methods 297 patients with locally advanced rectal cancer (cT3-4 or cN+) who were treated with neo-CRT followed by TME were retrospectively reviewed. Clinical characteristics including age, gender, tumor distance from anus, serum CEA, hemoglobin levels before treatment and clinical TN stage were used to investigate the association with pCR after neo-CRT. Results Seventy-nine (26.6%) patients achieved pCR after neo- CRT. pCR were achieved in 42 (34.4%) patients in cT1-3 stage and 37 (21.1%) in cT4 stage. pCR rate was 36.4% and 16.4% for serum CEA ≤5.33ng/ml and >5.33ng/ml before treatment, respectively. Univariate and multivariate analyses revealed serum CEA level ≤5.33ng/ml before treatment and clinical T stage, (i.e., cT1-3 versus cT4) were highly correlated with pCR (P < 0.05). Conclusion Clinical T stage and serum CEA level before treatment were strongly associated with pCR for patients with locally advanced rectal cancer treated with neo-CRT