Impact of early tumour shrinkage and resection on outcomes in patients with wild-type RAS metastatic colorectal cancer

Background Tumour shrinkage (TS) increases the possibility of resection in metastatic colorectal cancer (mCRC) and may improve tumour-related symptoms. Here we report prespecified secondary response-related end-points and exploratory TS/resection outcomes for patients with RAS wild-type (WT) tumours (no mutations in KRAS/NRAS exons 2/3/4) from the PRIME study (NCT00364013). Methods PRIME was a randomised phase 3 study comparing first-line panitumumab + FOLFOX4 versus FOLFOX4 in mCRC patients. Tumour response analyses were conducted to compare response rates and their impact on survival outcomes. Results Overall, 505 patients had RAS WT mCRC. More patients receiving panitumumab + FOLFOX4 versus FOLFOX4 had ≥30% (59% versus 38%; P < 0.001) or ≥20% (72% versus 57%; P < 0.001) TS at week 8 (early TS); consistent TS benefits were observed over the first ∼40 weeks of treatment. Objective response rate (P = 0.003), duration of response (P = 0.0027), depth of response (P = 0.0149), progression-free survival (PFS; P = 0.0015) and overall survival (OS; P = 0.0057) were improved in the panitumumab + FOLFOX4 group. Both early TS and resection were associated with improved PFS and OS. 2-year OS rates for patients who did (n = 64) versus did not (n = 441) undergo resection were 88% versus 40%; 2-year OS rates for patients who did (n = 45) versus did not (n = 460) undergo complete resection were 96% versus 41%. Conclusions More patients receiving panitumumab + FOLFOX4 versus FOLFOX4 had ≥30% or ≥20% TS at week 8; PFS and OS were also improved with panitumumab + FOLFOX4. The clinical value of achieving early TS in mCRC warrants further investigation.