Introduction: Three doses of SARS-CoV-2 mRNA vaccines have been recommended for cancer patients to reduce the risk of severe disease. Anti-neoplastic treatment, such as chemotherapy, may affect long-term vaccine immunogenicity. Method: Patients with solid or haematological cancer were recruited from 2 hospitals between July 2021 and March 2022. Humoral response was evaluated using GenScript cPASS surrogate virus neutralisation assays. Clinical outcomes were obtained from medical records and national mandatory-reporting databases. Results: A total of 273 patients were recruited, with 40 having haematological malignancies and the rest solid tumours. Among the participants, 204 (74.7%) were receiving active cancer therapy, including 98 (35.9%) undergoing systemic chemotherapy and the rest targeted therapy or immunotherapy. All patients were seronegative at baseline. Seroconversion rates after receiving 1, 2 and 3 doses of SARS-CoV-2 mRNA vaccination were 35.2%, 79.4% and 92.4%, respectively. After 3 doses, patients on active treatment for haematological malignancies had lower antibodies (57.3%±46.2) when compared to patients on immunotherapy (94.1%±9.56, P<0.05) and chemotherapy (92.8%±18.1, P<0.05). SARS-CoV-2 infection was reported in 77 (28.2%) patients, of which 18 were severe. No patient receiving a third dose within 90 days of the second dose experienced severe infection. Conclusion: This study demonstrates the benefit of early administration of the third dose among cancer patients. Keywords: Cancer, oncology, SARS-CoV-2, third dose, vaccination

3584 Background: Trifluridine/tipiracil (TAS-102) is currently approved as third-line treatment in metastatic colorectal cancer (mCRC). However, there is paucity of real-world data on the tolerability and efficacy with biweekly dosing as monotherapy or in combination with bevacizumab. In this study, we present our center’s experience with biweekly TAS-102 with or without bevacizumab in mCRC patients (pts). Methods: We performed a single center retrospective observational study of pts receiving TAS-102 between 2018 and 2021. Results: A total of 83 pts were included (53 men, 30 women), with a median age of 64 years. Majority of pts were treated with TAS-102 in the 3rd-line (48.2%) and 4th-line (28.9%) setting. Almost all (94.0%) were of ECOG ≤ 1 at the initiation of treatment. The mean number of cycles administered was 3.8 and bevacizumab (5mg/kg on Day 1, every 2 weeks) was used in combination with TAS-102 in 18 pts (21.7%). Majority of pts (84.3%) were given TAS-102 using the biweekly regimen (35mg/m2 BD, on Day 1-5 and 15-19, q28 days) rather than standard regimen (35mg/m2 BD, on Day 1-5 and 8-12, q28 days) following a change in institutional practice. Fifteen pts (18.1%) had their initial dose reduced to 30mg/m2 BD at prescriber's discretion. Median PFS and OS were 2.37 and 10.15 months, respectively. In terms of tolerability, fatigue (any grade, 42.2%) and neutropenia (any grade, 44.6%) were the two most common adverse events reported. Grade 3 or higher neutropenia and febrile neutropenia were 16.9% and 3.6%, respectively. Dose reduction during treatment was required in 15 pts (18.1%), dose delay in 31 pts (37.3%) and six pts (7.2%) discontinued treatment due to toxicity. More than half (54.2%) had at least an additional line of therapy (regorafenib, clinical trials or re-challenge previous chemotherapy agents) following disease progression with TAS-102. Conclusions: We report the largest real-world experience with biweekly TAS-102. Our pts treated with TAS-102 had comparable median PFS to the RECOURSE cohort but with significantly better OS as more than half continued to receive treatment. Biweekly dosing of TAS-102 with or without bevacizumab is well tolerated with significantly lower rates of Grade 3 neutropenia compared to the published data in the literature.

6649 Background: The risk of recurrence for colorectal cancer (CRC) is low after 5 years (<1.5% per year) hence, surveillance visits, CEA blood tests and annual CT scans are not recommended beyond this period (NCCN guidelines). Importantly, right-siting survivorship care to the community allows primary care providers (PCP) to focus on preventive health beyond cancer. The National University Cancer Institute, Singapore, a tertiary, academic cancer center developed a program to transition CRC survivorship care to the community after 5-years of active surveillance. Patients (Pts) are discharged to the community with a survivorship care plan and followed-up via phone calls. We hypothesize that by transitioning CRC survivors to the community, we can optimize healthcare resources by reducing specialist visits and tests at the cancer center without compromising outcomes. Methods: From July 2018, CRC pts beyond 5-years from diagnosis with no evidence of cancer recurrence were eligible for transition. Pts were followed prospectively to determine date of cancer recurrence, issues preventing transition to the community and a phone survey on pt satisfaction was conducted for those who transitioned to primary care. Data on healthcare utilization amongst pts who transitioned vs. pts who remained in tertiary care was collected. Data cutoff was June 2022. Statistical analysis was performed with IBM SPSS Statistics (v28.0). Results: Between July 2018 - June 2022, there were 791 CRC pts who were eligible for transition, of which 534 pts (67.5%) had no clinical issues preventing transition and included in this analysis. 54.3% (N= 290) were males and stage distribution of cancers were 14.2%, 34.0%, 47.1% and 4.7% for stages I, II, III and IV, respectively. The mean number of years since diagnosis was 6.88 (range: 5-16 years; SD 2.25). 380 pts (71.2%) were transitioned to the community. There was consistently higher utilization of healthcare resources in the group not transitioned vs. transitioned: mean number of consults (2.86 vs 1.02; p<0.001); CEA (1.23 vs 0.31; p<0.001); CT scans (0.08 vs 0.05; p=0.221) and colonoscopies (0.25 vs 0.16; p=0.031). Mean healthcare expenditure (mean gross bill per year) was consistently higher in pts across all categories for the group not transitioned vs. transitioned: consults ($158 vs $56; p<0.001); CT scans ($60 vs $39; p=0.273); CEA ($26 vs $7; p<0.001) and colonoscopies ($208 vs $126; p=0.018). Importantly, recurrence rates were low with no difference in both groups (0.8% vs 1.3%; p=0.629). 82% of CRC pts were satisfied or very satisfied with follow-up care provided by their PCPs on a subsequent survey. Conclusions: We have demonstrated value-driven survivorship care by right-siting CRC survivors into the community. Healthcare resources were optimized with reduction in specialist visits and tests which lead to lower costs while recurrence rates remain low. Pt satisfaction in the community was also high.