Oral maintenance capecitabine versus active monitoring for patients with metastatic colorectal cancer (mCRC) who are stable or responding after 16 weeks of first-line treatment: Results from the randomized FOCUS4-N trial

3504 Background: There is extensive randomised evidence supporting the use of treatment breaks in mCRC, but breaks from treatment are not universally offered to patients despite reductions in toxicity, without detriment to OS. Prior trials have shown that the combination of Cp and bevacizumab extend PFS but not OS. FOCUS4-N explores oral maintenance Cp monotherapy in patients with disease control on first line therapy. Methods: FOCUS4 was a molecularly stratified trial programme registering patients with newly diagnosed mCRC from 88 hospitals in the UK. Whilst undergoing 16 wks of first line treatment, a sample of tumour was sent for laboratory testing to stratify their disease into molecular subtypes: MSI, BRAF, PIK3CA, TP53 and RAS mutations. For some molecular groups, a targeted therapy subtrial was available but entry into the FOCUS4-N trial was offered to those in whom a targeted subtrial was unavailable. Patients were randomised 1:1 between maintenance Cp therapy or AM. The primary outcome was PFS assessed using 8-wkly RECIST reported CT scans with quality of life (using EQ5D 8 weekly) and OS as secondary outcomes. Toxicity and tolerability were assessed 4-wkly. On progression, from the nadir, patients recommenced first line treatment. Cox regression was used to assess efficacy by intention-to-treat (ITT) with adjustment for tumour location, WHO status, metastatic burden, first line treatment and biomarker subtype. Results: Between March 2014 and March 2020, 254 patients were randomised (127 to Cp and 127 to AM). Baseline characteristics were balanced between groups but event rates were higher than anticipated in the AM group and the final analysis was triggered early as a result of the COVID-19 pandemic halting recruitment. The table presents results for PFS and OS. Compliance with treatment was good with per-protocol analysis results very similar to ITT (PFS HR=0.38 (95% CI 0.28-0.51)). Toxicity from Cp v AM was as expected with G≥2 fatigue (25% v 12%), diarrhoea (23% v 13%) and hand-foot syndrome (26% v 3%). Quality of life showed no statistically significant differences between the two arms. Conclusions: Despite strong evidence of prolongation of PFS with maintenance therapy, OS remains unaffected and FOCUS4-N provides additional evidence to support the use of treatment breaks as a safe management alternative for patients who are stable or responding well to first line treatment for mCRC. Cp without bevacizumab may be used to extend PFS, in the interval after 16 weeks of combination therapy. Clinical trial information: ISRCTN#90061546. [Table: see text]