Can lung cancer be missed on an x-ray?

Easily: Some cancers do not ever show up on x-ray, others look like pneumonia. A chest ct is often needed.

Yes: Unfortunately there is a limit to the resolution of a chest x-ray. Small lesions can be missed. In addition, a chest xray is just a 2 dimensional projection comparing desities of different structures. If a tumor happens to overlap with another structure of the same density then you can't even see it. A ct scan can give a higher resolution picture but even it can miss a tumor at times.

Yes: Especially, if they are near the point at which the vessels and airways enter the lung, they can be concealed by the other solid tissues. Or a cancer may be masked by the pneumonia it causes by plugging an airway, or be too small to resolve on a chest plain film.

Yes it can: Sensitivity and specificity of chest x-ray to diagnose lung nodule/cancer are not perfect. Small nodules can be easily missed on chest x-ray. Ct scan will be more sensitive-compared to chest x-ray - in picking up small nodules.