Smoking cigarettes is bad for your health in many ways, but it particularly affects the lungs. The toxins within cigarettes can cause cells to multiply out of control, leading to the development of lung cancer. The cancer that is most commonly caused by smoking is squamous cell carcinoma (SCC) of the lung.

Under the microscope, SCC tumour cells are scattered in small nests as it has grown through the lung tissue, disrupting the usual lung pattern. Compression of the alveoli makes the tumour stand out as it is much denser than the surrounding lung tissue. This change in density within the lung enables lung cancers to be seen on x-ray imaging. The tumour cells have large and irregular shaped nuclei (centres), with individual cells often being seen dividing.