ESTRO 36 Abstract Book

S369 ESTRO 36 _______________________________________________________________________________________________

we have applied a multiplex magnetic bead panel (Luminex ® ) to explore associations between serum proteins and treatment outcome in patients with locally

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advanced rectal cancer. Material and Methods

Serum samples from 22 rectal cancer patients were collected at the time of diagnosis. All patients underwent neoadjuvant long-course chemoradiotherapy (CRT), according to current national guidelines. Surgery was performed 6-8 weeks after completion of CRT and five patients underwent adjuvant chemotherapy. CRT responses were evaluated by ypTN staging and tumour regression grade (TRG) (College of American Pathologists system) scoring. The median follow-up time was 21 months (range 1-34). Using multiplex magnetic bead technology (Luminex ® , R&D systems), a manually selected panel of 86 proteins involved in angiogenesis, hypoxia and metastasis was applied to analyse serum samples. Associations were explored using two-sided Student’s t- tests, with p-values < 0.05 considered statistically significant. The STRING (Search Tool for the Retrieval of Interacting Genes/Proteins) database (string-db.org) was used to predict interaction networks. Survival differences were assessed by the log-rank test and visualised by the Kaplan-Meier method. Results Significant associations between several serum proteins and TNM, ypTN, TRG and progression-free survival (PFS) were detected. STRING analysis identified that a majority of these proteins were involved in the PI3K-Akt signaling pathway, and particularly angiopoietin-2 (ANGPT2) and platelet-derived growth factor subunit B (PDGFB) were associated to multiple end-points. By combining ANGPT2 and PDGFB, high levels were associated with both poor histopathologic outcome (ypT3-4 versus ypT0-2: p=0.040; TRG2-3 versus TRG1: p=0.015) (Table 1) and PFS (cut-off 8700 pg/ml, p-value 0.031), with all PFS events being development of liver metastasis (Figure 1).

Conclusion Tumour angiogenesis is a major mechanism in sustained tumour progression and the metastatic process. In the current study, our main finding was that high serum levels of the angiogenic factors ANGPT2 and PDGFB identified patients with poor histopathologic response to neoadjuvant CRT, who subsequently progressed rapidly to metastatic disease. These results may point out an escalating tumour aggressiveness paralleled by increasing angiogenesis. The results were achieved in a small cohort and require validation, but may represent an approach for early selection of patients with an aggressive tumour phenotype for intensified treatment strategies, perhaps also with combinatory regimens targeting angiogenesis. The results are currently being validated in an independent patient cohort. PO-0705 Work ability in Dutch rectal cancer patients during the first year of treatment A.M. Couwenberg 1 , M.P.W. Intven 1 , J.P.M. Burbach 1 , L. Hupkens 2 , W.M.U. Van Grevenstein 3 , H.M. Verkooijen 4 1 UMC Utrecht, Radiotherapy, Utrecht, The Netherlands 2 Blik op Werk, Quality and research institute on workability, Utrecht, The Netherlands 3 UMC Utrecht, Surgery, Utrecht, The Netherlands 4 UMC Utrecht, Imaging Division, Utrecht, The Netherlands Purpose or Objective Rectal cancer treatment is associated with substantial morbidity and decreased quality of life. The impact of treatment on workability has hardly been studied. In this study we evaluated workability in rectal cancer patients during the first year of treatment. Material and Methods All working-aged rectal cancer patients (<67 years) within the Dutch prospective colorectal cancer cohort referred for radiotherapy at the UMC Utrecht between February 2013 and January 2016 were selected. Workability was assessed with the Work Ability Index (WAI) Questionnaire before start of treatment and at 3, 6 and 12 months. The WAI score, ranging from 7 to 49, was calculated for patients with paid employment at time of assessment and who completed at least one questionnaire. Higher scores reflect better workability. Workability was categorized in poor (7-27), moderate (28-36), good (37-43) and excellent (44-49). Results were stratified for treatment strategies and compared with scores of the age-matched Dutch reference population. Results

Table 1 ANGPT2 and PDGFB