Adenocarcinomas of the lung tend to be located more peripherally and are usually smaller in comparison to pulmonary squamous cell carcinomas. The relative proportions of various histologic types of lung cancer have changed over the years. Compared to the 1970ís and 80ís, the proportion of adenocarcinoma has increased recently and it is now the commonest type, whereas squamous cell carcinoma, small cell carcinoma, and large cell carcinoma cases have declined. These trends are likely related to the changes in design and characteristics of manufactured cigarettes. The relative proportion of various histologic types of lung cancer are as follows: Adenocarcinoma 38%; Squamous Cell Carcinoma 20%; Small Cell Carcinoma 14%; Large Cell Carcinoma 3%; Other types 25%. Mixed histologic patterns e.g. Adenocarcinoma + Squamous Cell Carcinoma OR Squamous Cell Carcinoma + Small Cell Carcinoma etc. occur in about 10% of cases. The image shows invasive adenocarcinoma of lung in a 72 y/o female. The tumor involves the right lower lobe. There are extensive intrapulmonary metastases (lymphangitic carcinomatosis) seen as whitish-gray nodules throughout both lungs. There is bronchopneumonia of left lower lobe. Image copyright: pathorama.ch.