Treatment sequencing and outcomes in synchronous metastatic rectal cancer.

750 Background: Optimal sequencing of therapies in synchronous metastatic rectal cancer (SMRC) remains unknown. Aim: To compare sequencing of treatment modality and outcomes in SMRC. Methods: Retrospective audit of patients with SMRC registered on the multi-centre Treatment of Recurrent and Advanced Colorectal Cancer database between 1/1/2009 and 30/6/2015. Patients were grouped according to initial treatment mode: chemotherapy (C), chemoradiation (CRT), surgery (S) and best supportive care (BSC). Results: 247 patients were identified: median age was 62yrs, ECOG 0-1 87%, male 64%, 1-2 metastatic sites 86% (liver 56%) and treatment intent was curative in 14%. Median follow-up was 19m. Primary tumour resection occurred in 95 patients (38%). Compared to no resection, these patients had improved median OS (41 vs 16 months; p < 0.0001) and PFS (15 vs 10 months; p < 0.0001). There was no difference in outcome with varying treatment combinations and sequences of S with CRT/C (p > 0.05). For unresected patients, the most common initial treatment was C (30%). Any active treatment was associated with better OS compared to BSC (6.4m): C (16.1m, p < 0.0001), CRT (20.6m, p = 0.001) and C&CRT (21.8m, p < 0.0001). Most active treatments were associated with better PFS compared to BSC (6.4m): C (10.8m, p = 0.015) and C&CRT (10.6m, p = 0.012). There was no significant PFS difference comparing BSC to CRT (p = 0.25). There were no OS nor PFS differences between: comparisons of C, CRT and C&CRT (p > 0.05). Initial treatment strategies were compared for 129 patients receiving multimodal therapy, where 22 (17%) had initial treatment with C (60% subsequent resection) compared to 85 (66%) commencing with CRT (70% subsequent resection). Commencing with CRT was associated with a longer OS compared to C (31 vs 21 months; p = 0.014). Conclusions: For patients undergoing primary tumour resection, no difference in outcomes were demonstrated with the addition of C and/or CRT. For unresected patients, there was a survival benefit associated with active therapy, with no significant difference between C, CRT or C&CRT. This supports the current practice of using these modalities at clinicians’ discretion. Review of patient factors potentially influencing treatment choice is ongoing.