This manuscript addresses the role of O(6)-methylguanine-DNA methyltransferase (MGMT) as a biomarker in the oncogenesis of cancer and the opportunity of turning this gene into a drugable target in neuroendocrine tumours of the lung. Studies in brain tumours conclude that MGMT promoter methylation is considered a strong predictive factor for a favourable outcome for treatment with temozolomide, e.g. alkylating agent. We conducted a systematic review of MGMT in non-small cell lung cancer (NSCLC), small-cell lung cancer (SCLC) and other pulmonary neuroendocrine tumours (NETs) to evaluate whether MGMT is a prognostic and/or predictive factor to select patients with lung cancer who can benefit from treatment with temozolomide. In NSCLC MGMT promoter methylation is not a prognostic and predictive factor, hence temozolomide has no place. In SCLC and NET patients with a MGMT promoter methylation benefit of temozolomide has to be confirmed.Temozolomide can be considered a 'personalized' treatment if the predictive role of MGMT is further confirmed.