What could cause a lung nodule to thicken?

Growth: If a lung nodule thickens, that means it is growing. Whether this is cancer, infection or anything else, you need to find out.

Lung nodule: A lung nodule can be anything: infection, an old scar, a dormant organism, a cluster of inflammatory cells, or cancer. It cannot be evaluated without context. A nodule in a smoker who's 70 yo is different from that of someone young, nonsmoker, living in an area known for valley fever for ex. All of the above can thicken. Scar becomes evident. Cancer progresses. Or an infection grows. See your doc.