BackgroundPrevious studies have reported the prognostic impact of primary tumor sidedness in metastatic colorectal cancer (mCRC) and its influence on cetuximab efficacy. The present retrospective analysis of two panitumumab trials investigated a possible association between tumor sidedness and treatment efficacy in first-line mCRC patients with RAS wild-type (WT) primary tumors.Materials and methodsData from two randomized first-line panitumumab trials were analyzed for treatment outcomes by primary tumor sidedness for RAS WT patients. PRIME (phase 3; NCT00364013) compared panitumumab plus FOLFOX versus FOLFOX alone; PEAK (phase 2; NCT00819780) compared panitumumab plus FOLFOX versus bevacizumab plus FOLFOX. Primary tumors located in the cecum to transverse colon were coded as right-sided, while tumors located from the splenic flexure to rectum were considered left-sided.ResultsTumor sidedness ascertainment (RAS WT population) was 83% (n = 559/675); 78% of patients (n = 435) had left-sided and 22% (n = 124) had right-sided tumors. Patients with right-sided tumors did worse for all efficacy parameters compared with patients with left-sided disease in the RAS WT population and also in the RAS/BRAF WT subgroup. In patients with left-sided tumors, panitumumab provided better outcomes than the comparator treatment, including on median overall survival (PRIME: 30.3 versus 23.6 months, adjusted hazard ratio = 0.73, P = 0.0112; PEAK: 43.4 versus 32.0 months, adjusted hazard ratio = 0.77, P = 0.3125).ConclusionThe results of these retrospective analyses confirm that in RAS WT patients, right-sided primary tumors are associated with worse prognosis than left-sided tumors, regardless of first-line treatment received. RAS WT patients with left-sided tumors derive greater benefit from panitumumab-containing treatment than chemotherapy alone or combined with bevacizumab, including an overall survival advantage (treatment difference: PRIME 6.7 months; PEAK 11.4 months). No final conclusions regarding optimal treatment could be drawn for RAS WT patients with right-sided mCRC due to the relatively low number of paxtients. Further research in this field is warranted.Trial registration (Clinicaltrials.gov)PRIME (NCT00364013), PEAK (NCT00819780).

Purpose: We evaluated the influence of RAS mutation status on the treatment effect of panitumumab in a prospective-retrospective analysis of a randomized, multicenter phase III study of panitumumab plus fluorouracil, leucovorin, and irinotecan (FOLFIRI) versus FOLFIRI alone as second-line therapy in patients with metastatic colorectal cancer (mCRC; ClinicalTrials.gov, NCT0039183).Experimental Design: Outcomes were from the study's primary analysis. RAS mutations beyond KRAS exon 2 (KRAS exons 3, 4; NRAS exons 2, 3, 4; BRAF exon 15) were detected by bidirectional Sanger sequencing in wild-type KRAS exon 2 tumor specimens. Progression-free survival (PFS) and overall survival (OS) were coprimary endpoints.Results: The RAS ascertainment rate was 85%; 18% of wild-type KRAS exon 2 tumors harbored other RAS mutations. For PFS and OS, the hazard ratio (HR) for panitumumab plus FOLFIRI versus Patients with RAS mutations were unlikely to benefit from panitumumab. Among RAS wild-type patients, the objective response rate was 41% in the panitumumab-FOLFIRI group versus 10% in the FOLFIRI group.Conclusions: Patients with RAS mutations were unlikely to benefit from panitumumab-FOLFIRI and the benefit-risk of panitumumab-FOLFIRI was improved in the wild-type RAS population compared with the wild-type KRAS exon 2 population. These findings support RAS testing for patients with mCRC.

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.

These retrospective analyses have confirmed that RAS WT right-sided mCRC is associated with a poor prognosis, regardless of the treatment. RAS WT patients with left-sided tumors benefitted from the addition of panitumumab in second or later treatment lines. Further research is warranted to determine the optimum management of right-sided mCRC and RAS MT tumors.

PurposeTo report exploratory analyses of early tumour shrinkage (ETS) and depth of response (DpR) in patients with RAS wild-type (WT) metastatic colorectal cancer (mCRC), receiving the first-line treatment in three randomised panitumumab trials. MethodsData from the PRIME (NCT00364013), PEAK (NCT00819780) and PLANET (NCT00885885) studies were included. Median DpR, the proportion of patients achieving ETS ≥ 20% or ≥ 30% at week 8, and the impact of ETS and DpR (including by category) on outcome were analysed. Factors associated with ETS and DpR and the optimal ETS/DpR cut-off values for predicting improved overall survival (OS) were assessed.ResultsOverall, 505, 170 and 53 patients had RAS WT mCRC in PRIME, PEAK and PLANET, respectively. Patients receiving panitumumab had higher ETS rates (≥ 30%: PRIME 59% vs. 38%; PEAK 64% vs. 45%) and greater DpR (PRIME: 54% vs. 46%; PEAK: 65% vs. 46%) than those receiving treatment without panitumumab. In multiple regression analyses, panitumumab treatment, liver-only metastases and WT BRAF status were consistently associated with improved ETS and DpR outcomes. Irrespective of treatment, ETS and DpR were associated with improved progression-free survival, overall survival and resection rates; most resections occurred in patients in the two highest DpR categories. In PRIME and PEAK, respectively, the optimal cut-offs for predicting improved OS were 32 and 34% for ETS, and 59 and 70% for DpR.ConclusionsThese exploratory analyses suggest that panitumumab is associated ETS and DpR benefits in patients with RAS WT mCRC and that achieving these endpoints during first-line treatment is linked with favourable outcomes.Electronic supplementary materialThe online version of this article (doi:10.1007/s00432-017-2534-z) contains supplementary material, which is available to authorized users.

This meta-analysis supports a potential benefit for first-line EGFRI plus chemotherapy versus bevacizumab plus chemotherapy with respect to OS, ORR and ETS in patients with RAS WT mCRC. A patient-level meta-analysis is awaited.

First-line panitumumab was associated with improved ETS and DpR vs. comparator in patients with left-sided mCRC. ETS may identify a subgroup of patients with right-sided disease who might respond to panitumumab.

Panitumumab is approved for RAS wild‐type metastatic colorectal cancer and was evaluated in Phase III (PRIME, NCT00364013) and Phase II (PEAK, NCT00819780) first‐line randomised studies. This retrospective analysis of these trials investigated efficacy and toxicity of panitumumab‐based maintenance after oxaliplatin discontinuation in RAS wild‐type patients. First‐line regimens were FOLFOX4 ± panitumumab in PRIME and mFOLFOX6 plus panitumumab or mFOLFOX6 plus bevacizumab in PEAK. Outcomes included median progression‐free survival (PFS) and overall survival (OS), from randomisation and oxaliplatin discontinuation, and toxicity. Overall, median duration of panitumumab plus 5‐fluorouracil/leucovorin (5‐FU/LV) maintenance was 21 (interquartile range: 11–41) weeks; that of 5‐FU/LV ± bevacizumab maintenance was 16 (6–31) weeks. Median OS from randomisation was 40.2 (95% confidence interval: 30.3–50.4) and 39.1 (34.2–63.0) months for panitumumab plus 5‐FU/LV maintenance and 24.1 (17.7–33.0) and 28.9 (21.0–32.0) months for 5‐FU/LV ± bevacizumab maintenance in PRIME and PEAK, respectively. Median PFS from randomisation was 16.6 (11.3–23.6) and 15.4 (11.6–18.4) months for panitumumab plus 5‐FU/LV maintenance and 12.6 (9.4–16.2) and 13.1 (9.5–16.6) months for 5‐FU/LV ± bevacizumab maintenance in PRIME and PEAK, respectively. From oxaliplatin discontinuation, median OS was 33.9 (24.7–42.8) and 33.5 (24.5–54.9) months for panitumumab plus 5‐FU/LV maintenance and 16.4 (12.4–24.1) and 23.3 (15.7–26.3) months for 5‐FU/LV ± bevacizumab maintenance in PRIME and PEAK, respectively; PFS was 11.7 (7.8–19.2) and 9.7 (5.8–14.8) months and 7.1 (5.6–10.2) and 7.0 (3.9–10.6) months, respectively. The most frequently reported adverse events were rash, fatigue and diarrhoea. Maintenance of panitumumab plus 5‐FU/LV after oxaliplatin discontinuation was well tolerated and may be an acceptable treatment paradigm for patients demonstrating a good response to first‐line treatment. Prospective studies are warranted.