The primary research objective of this observational study in pretreated patients with NSCLC of Stage IIIa/b or Stage IV is to evaluate patients' Karnofsky Index (KI) after the second cycle of second-line treatment with single agent pemetrexed in a real life setting, and to evaluate factors potentially influencing performance status in terms of KI, i.e. frequency of use of concomitant medications, in particular analgesics, folic acid, Vitamin B12, antiemetics, and medications against diarrhea; as documented in patient diary (days of use per week) and by the physicians.