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Pulmonary neuroendocrine neoplasms (NENs) are a heterogeneous group of tumors of the neuroendocrine cells, which are diffusely interspersed throughout the respiratory system. Two families of NEN are established according to histological grading: the well-differentiated neuroendocrine tumors (NETs) and the high-grade neuroendocrine carcinomas (NECs). Four types of NEN are recognized, including two NETs represented by typical carcinoid (TC) and atypical carcinoid (AC) and two NECs represented by large cell neuroendocrine carcinoma (LCNEC) and small cell lung carcinoma (SCLC).

Imaging plays a key role in the assessment of response to therapy in lung cancer, particularly in the definition of disease progression/reduction after chemotherapy (ChT) and/or radiotherapy (RT) and in the subsequent management of the patient. Tumour response criteria have been introduced aiming at standardizing results in cancer treatments. However, measurement errors and limits of such parameters, as well as the complex imaging response patterns observed after the use of newer personalized pharmacological treatments for non-small-cell lung cancer (NSCLC), pose a challenge in the application of common standardized criteria for the response evaluation. The tumour response after RT can present with different patterns and timing, highly dependent on the techniques used. One of the major issues is distinguishing radiation-induced lung injury/disease (RILI/RILD) from tumour recurrence. Therefore, response assessment in lung cancer should evolve according to the advances in lung cancer treatment and the introduction of newer diagnostic techniques, including functional and molecular imaging.