PD-L1 Expression in Cancer (PECan Study).

Inclusion Criteria: * Aged 18 or above * Patients with histologically confirmed NSCLC or melanoma scheduled for PD1/PDL1 immunotherapy alone or in combination with other systemic anti-cancer therapy. * Willingness and ability to comply with scheduled study visits and tests. Exclusion Criteria: * Pregnant or lactating women * Concomitant uncontrolled medical conditions * Patients likely to require palliative radiotherapy within the first 12 weeks of treatment or radiotherapy to target lesion(s) received within preceding 42 days * More than 3 months between IHC PDL1 and study recruitment * Patients who have received other systemic anti-cancer therapy within preceding 14 days * Prognosis less than 3 months * Previous anticancer treatment with any checkpoint inhibitor or other immunotherapy, i.e. only immunotherapy naïve patients