br Adjuvant chemotherapy has proved to be
Adjuvant chemotherapy has proved to be of benefit in patients with stage IIA-IIIB NSCLC , and though its use in stage IB patients re-mains controversial, many centers oﬀer adjuvant chemotherapy to pa-tients with tumors ≥4 cm . In our cohort, 20.4% with stage IA disease surprisingly received adjuvant chemotherapy while the ma-jority of patients with stage IB disease did not receive any adjuvant therapy. A subgroup analysis in stage IIA-IIIB patients with adeno-carcinoma or squamous cell carcinoma was undertaken and since the majority of NSCLC patients in our cohort had stage I disease, this de-cision resulted in less statistical power (n = 202). Nevertheless, uni-variate and multivariate Cox regression analysis showed a statistically significant positive impact on OS for c-MET H score ≥20. The PFS benefit was more profound in the multivariate analyses in this subgroup of patients. c-MET has been implicated in resistance to chemotherapy, including platinum , which would be in C 11BODIPY581 / 591 to our finding that a higher c-MET score is beneficial in patients treated with adjuvant platinum-based chemotherapy. On the other hand, c-MET has been implicated in the process of metastasis and our results may be explained by the fact that patients with a higher c-MET expression derive a greater benefit from adjuvant chemotherapy than those with a lower expres-sion.
The major limitation of our study is its retrospective nature making it prone to selection bias. There is also a risk of information bias re-garding missing data mostly on patients receiving adjuvant therapy. Information bias regarding c-MET H-scoring is limited due to the methodology used (see methods), but can not be avoided Tumour fixation is important for the reliability of IHC staining, because over-fixation or underfixation can cause false positive or false negative re-sults, respectively.Interobserver variability, a major problem in inter-preting IHC results, has been reduced in our study by considering the H-score as a continuous variable. Another consideration is that TMAs may not be representative of the entire tumour, because of intratumoral heterogeneity, this being a limitation in all published trials with IHC or H-scoring. Missing data regarding EGFR-mutation is not a major lim-itation since there is no evidence suggesting that it could be a con-founder in this context . However, there was a large number of patients included in our trial and we had available data regarding the use of adjuvant therapy for 444 patients. The real-life character of this cohort trial adds strength to the external validity of our results. Future trials should probably not be based on IHC alone. However, the use of MET kinase inhibitors for IHC positive or MET amplified tumors has not been fruitful. The exception might be patients with MET exon 14 skipping mutation positive tumors, where new treatments are currently under development . The importance of MET amplification or MET exon 14 skipping mutation as oncogenic drivers is still unclear. The development of conjugate drugs (c-MET antibodies with cytotoxic drug
combinations) might be the solution for the successful treatment of c-MET positive patients, and in such a case, the IHC expression of c-MET is the most relevant biomarker which should be tested.
Despite all the limitations mentioned above, we conclude that c-MET H score ≥20 was a positive prognostic biomarker for OS in our cohort of surgically resected NSCLC patients. This conclusion is based mostly on the results of the multivariate analysis in the whole study population. There is enough statistical evidence from our analyses to support that this benefit of c-MET positivity is most likely correlated to adjuvant chemotherapy, therefore rendering c-MET H-score ≥20 a possible predictive biomarker for platinum-based adjuvant che-motherapy. This result should be verified in a randomized setting and generates the hypothesis that c-MET could be used in the future for a more individualized selection of patients who receive adjuvant che-motherapy.
Conflict of interest
None of the authors has any relevant conflict of interest to declare.
Stockholm Cancer Society, Stockholm County Council.
Appendix A. Supplementary data
 I.H. Kim, et al., Clinical significance of C-MET overexpression and epidermal growth factor receptor mutation in platinum-based adjuvant chemotherapy out-come in surgically resected lung adenocarcinoma, Ann. Surg. Oncol. 24 (3) (2017) 770–777.
 W. Sterlacci, et al., MET overexpression and gene amplification: prevalence, clinico-pathological characteristics and prognostic significance in a large cohort of patients with surgically resected NSCLC, Virchows Arch. 471 (1) (2017) 49–55.